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-rw-r--r--kernel/rcu/tree.c5091
1 files changed, 5091 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
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--- /dev/null
+++ b/kernel/rcu/tree.c
@@ -0,0 +1,5091 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Read-Copy Update mechanism for mutual exclusion (tree-based version)
+ *
+ * Copyright IBM Corporation, 2008
+ *
+ * Authors: Dipankar Sarma <dipankar@in.ibm.com>
+ * Manfred Spraul <manfred@colorfullife.com>
+ * Paul E. McKenney <paulmck@linux.ibm.com>
+ *
+ * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * Documentation/RCU
+ */
+
+#define pr_fmt(fmt) "rcu: " fmt
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/nmi.h>
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/export.h>
+#include <linux/completion.h>
+#include <linux/kmemleak.h>
+#include <linux/moduleparam.h>
+#include <linux/panic.h>
+#include <linux/panic_notifier.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/mutex.h>
+#include <linux/time.h>
+#include <linux/kernel_stat.h>
+#include <linux/wait.h>
+#include <linux/kthread.h>
+#include <uapi/linux/sched/types.h>
+#include <linux/prefetch.h>
+#include <linux/delay.h>
+#include <linux/random.h>
+#include <linux/trace_events.h>
+#include <linux/suspend.h>
+#include <linux/ftrace.h>
+#include <linux/tick.h>
+#include <linux/sysrq.h>
+#include <linux/kprobes.h>
+#include <linux/gfp.h>
+#include <linux/oom.h>
+#include <linux/smpboot.h>
+#include <linux/jiffies.h>
+#include <linux/slab.h>
+#include <linux/sched/isolation.h>
+#include <linux/sched/clock.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/kasan.h>
+#include <linux/context_tracking.h>
+#include "../time/tick-internal.h"
+
+#include "tree.h"
+#include "rcu.h"
+
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "rcutree."
+
+/* Data structures. */
+
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
+ .gpwrap = true,
+#ifdef CONFIG_RCU_NOCB_CPU
+ .cblist.flags = SEGCBLIST_RCU_CORE,
+#endif
+};
+static struct rcu_state rcu_state = {
+ .level = { &rcu_state.node[0] },
+ .gp_state = RCU_GP_IDLE,
+ .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
+ .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
+ .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock),
+ .name = RCU_NAME,
+ .abbr = RCU_ABBR,
+ .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
+ .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
+ .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
+};
+
+/* Dump rcu_node combining tree at boot to verify correct setup. */
+static bool dump_tree;
+module_param(dump_tree, bool, 0444);
+/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
+static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
+#ifndef CONFIG_PREEMPT_RT
+module_param(use_softirq, bool, 0444);
+#endif
+/* Control rcu_node-tree auto-balancing at boot time. */
+static bool rcu_fanout_exact;
+module_param(rcu_fanout_exact, bool, 0444);
+/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
+static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
+module_param(rcu_fanout_leaf, int, 0444);
+int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
+/* Number of rcu_nodes at specified level. */
+int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
+int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
+
+/*
+ * The rcu_scheduler_active variable is initialized to the value
+ * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
+ * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
+ * RCU can assume that there is but one task, allowing RCU to (for example)
+ * optimize synchronize_rcu() to a simple barrier(). When this variable
+ * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
+ * to detect real grace periods. This variable is also used to suppress
+ * boot-time false positives from lockdep-RCU error checking. Finally, it
+ * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
+ * is fully initialized, including all of its kthreads having been spawned.
+ */
+int rcu_scheduler_active __read_mostly;
+EXPORT_SYMBOL_GPL(rcu_scheduler_active);
+
+/*
+ * The rcu_scheduler_fully_active variable transitions from zero to one
+ * during the early_initcall() processing, which is after the scheduler
+ * is capable of creating new tasks. So RCU processing (for example,
+ * creating tasks for RCU priority boosting) must be delayed until after
+ * rcu_scheduler_fully_active transitions from zero to one. We also
+ * currently delay invocation of any RCU callbacks until after this point.
+ *
+ * It might later prove better for people registering RCU callbacks during
+ * early boot to take responsibility for these callbacks, but one step at
+ * a time.
+ */
+static int rcu_scheduler_fully_active __read_mostly;
+
+static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
+ unsigned long gps, unsigned long flags);
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
+static void invoke_rcu_core(void);
+static void rcu_report_exp_rdp(struct rcu_data *rdp);
+static void sync_sched_exp_online_cleanup(int cpu);
+static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
+static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
+static bool rcu_rdp_cpu_online(struct rcu_data *rdp);
+static bool rcu_init_invoked(void);
+static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
+static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
+
+/*
+ * rcuc/rcub/rcuop kthread realtime priority. The "rcuop"
+ * real-time priority(enabling/disabling) is controlled by
+ * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration.
+ */
+static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
+module_param(kthread_prio, int, 0444);
+
+/* Delay in jiffies for grace-period initialization delays, debug only. */
+
+static int gp_preinit_delay;
+module_param(gp_preinit_delay, int, 0444);
+static int gp_init_delay;
+module_param(gp_init_delay, int, 0444);
+static int gp_cleanup_delay;
+module_param(gp_cleanup_delay, int, 0444);
+
+// Add delay to rcu_read_unlock() for strict grace periods.
+static int rcu_unlock_delay;
+#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
+module_param(rcu_unlock_delay, int, 0444);
+#endif
+
+/*
+ * This rcu parameter is runtime-read-only. It reflects
+ * a minimum allowed number of objects which can be cached
+ * per-CPU. Object size is equal to one page. This value
+ * can be changed at boot time.
+ */
+static int rcu_min_cached_objs = 5;
+module_param(rcu_min_cached_objs, int, 0444);
+
+// A page shrinker can ask for pages to be freed to make them
+// available for other parts of the system. This usually happens
+// under low memory conditions, and in that case we should also
+// defer page-cache filling for a short time period.
+//
+// The default value is 5 seconds, which is long enough to reduce
+// interference with the shrinker while it asks other systems to
+// drain their caches.
+static int rcu_delay_page_cache_fill_msec = 5000;
+module_param(rcu_delay_page_cache_fill_msec, int, 0444);
+
+/* Retrieve RCU kthreads priority for rcutorture */
+int rcu_get_gp_kthreads_prio(void)
+{
+ return kthread_prio;
+}
+EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
+
+/*
+ * Number of grace periods between delays, normalized by the duration of
+ * the delay. The longer the delay, the more the grace periods between
+ * each delay. The reason for this normalization is that it means that,
+ * for non-zero delays, the overall slowdown of grace periods is constant
+ * regardless of the duration of the delay. This arrangement balances
+ * the need for long delays to increase some race probabilities with the
+ * need for fast grace periods to increase other race probabilities.
+ */
+#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
+
+/*
+ * Return true if an RCU grace period is in progress. The READ_ONCE()s
+ * permit this function to be invoked without holding the root rcu_node
+ * structure's ->lock, but of course results can be subject to change.
+ */
+static int rcu_gp_in_progress(void)
+{
+ return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
+}
+
+/*
+ * Return the number of callbacks queued on the specified CPU.
+ * Handles both the nocbs and normal cases.
+ */
+static long rcu_get_n_cbs_cpu(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ if (rcu_segcblist_is_enabled(&rdp->cblist))
+ return rcu_segcblist_n_cbs(&rdp->cblist);
+ return 0;
+}
+
+void rcu_softirq_qs(void)
+{
+ rcu_qs();
+ rcu_preempt_deferred_qs(current);
+ rcu_tasks_qs(current, false);
+}
+
+/*
+ * Reset the current CPU's ->dynticks counter to indicate that the
+ * newly onlined CPU is no longer in an extended quiescent state.
+ * This will either leave the counter unchanged, or increment it
+ * to the next non-quiescent value.
+ *
+ * The non-atomic test/increment sequence works because the upper bits
+ * of the ->dynticks counter are manipulated only by the corresponding CPU,
+ * or when the corresponding CPU is offline.
+ */
+static void rcu_dynticks_eqs_online(void)
+{
+ if (ct_dynticks() & RCU_DYNTICKS_IDX)
+ return;
+ ct_state_inc(RCU_DYNTICKS_IDX);
+}
+
+/*
+ * Snapshot the ->dynticks counter with full ordering so as to allow
+ * stable comparison of this counter with past and future snapshots.
+ */
+static int rcu_dynticks_snap(int cpu)
+{
+ smp_mb(); // Fundamental RCU ordering guarantee.
+ return ct_dynticks_cpu_acquire(cpu);
+}
+
+/*
+ * Return true if the snapshot returned from rcu_dynticks_snap()
+ * indicates that RCU is in an extended quiescent state.
+ */
+static bool rcu_dynticks_in_eqs(int snap)
+{
+ return !(snap & RCU_DYNTICKS_IDX);
+}
+
+/*
+ * Return true if the CPU corresponding to the specified rcu_data
+ * structure has spent some time in an extended quiescent state since
+ * rcu_dynticks_snap() returned the specified snapshot.
+ */
+static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
+{
+ return snap != rcu_dynticks_snap(rdp->cpu);
+}
+
+/*
+ * Return true if the referenced integer is zero while the specified
+ * CPU remains within a single extended quiescent state.
+ */
+bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
+{
+ int snap;
+
+ // If not quiescent, force back to earlier extended quiescent state.
+ snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
+ smp_rmb(); // Order ->dynticks and *vp reads.
+ if (READ_ONCE(*vp))
+ return false; // Non-zero, so report failure;
+ smp_rmb(); // Order *vp read and ->dynticks re-read.
+
+ // If still in the same extended quiescent state, we are good!
+ return snap == ct_dynticks_cpu(cpu);
+}
+
+/*
+ * Let the RCU core know that this CPU has gone through the scheduler,
+ * which is a quiescent state. This is called when the need for a
+ * quiescent state is urgent, so we burn an atomic operation and full
+ * memory barriers to let the RCU core know about it, regardless of what
+ * this CPU might (or might not) do in the near future.
+ *
+ * We inform the RCU core by emulating a zero-duration dyntick-idle period.
+ *
+ * The caller must have disabled interrupts and must not be idle.
+ */
+notrace void rcu_momentary_dyntick_idle(void)
+{
+ int seq;
+
+ raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
+ seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
+ /* It is illegal to call this from idle state. */
+ WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
+ rcu_preempt_deferred_qs(current);
+}
+EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
+
+/**
+ * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
+ *
+ * If the current CPU is idle and running at a first-level (not nested)
+ * interrupt, or directly, from idle, return true.
+ *
+ * The caller must have at least disabled IRQs.
+ */
+static int rcu_is_cpu_rrupt_from_idle(void)
+{
+ long nesting;
+
+ /*
+ * Usually called from the tick; but also used from smp_function_call()
+ * for expedited grace periods. This latter can result in running from
+ * the idle task, instead of an actual IPI.
+ */
+ lockdep_assert_irqs_disabled();
+
+ /* Check for counter underflows */
+ RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0,
+ "RCU dynticks_nesting counter underflow!");
+ RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0,
+ "RCU dynticks_nmi_nesting counter underflow/zero!");
+
+ /* Are we at first interrupt nesting level? */
+ nesting = ct_dynticks_nmi_nesting();
+ if (nesting > 1)
+ return false;
+
+ /*
+ * If we're not in an interrupt, we must be in the idle task!
+ */
+ WARN_ON_ONCE(!nesting && !is_idle_task(current));
+
+ /* Does CPU appear to be idle from an RCU standpoint? */
+ return ct_dynticks_nesting() == 0;
+}
+
+#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
+ // Maximum callbacks per rcu_do_batch ...
+#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
+static long blimit = DEFAULT_RCU_BLIMIT;
+#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
+static long qhimark = DEFAULT_RCU_QHIMARK;
+#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
+static long qlowmark = DEFAULT_RCU_QLOMARK;
+#define DEFAULT_RCU_QOVLD_MULT 2
+#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
+static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
+static long qovld_calc = -1; // No pre-initialization lock acquisitions!
+
+module_param(blimit, long, 0444);
+module_param(qhimark, long, 0444);
+module_param(qlowmark, long, 0444);
+module_param(qovld, long, 0444);
+
+static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
+static ulong jiffies_till_next_fqs = ULONG_MAX;
+static bool rcu_kick_kthreads;
+static int rcu_divisor = 7;
+module_param(rcu_divisor, int, 0644);
+
+/* Force an exit from rcu_do_batch() after 3 milliseconds. */
+static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
+module_param(rcu_resched_ns, long, 0644);
+
+/*
+ * How long the grace period must be before we start recruiting
+ * quiescent-state help from rcu_note_context_switch().
+ */
+static ulong jiffies_till_sched_qs = ULONG_MAX;
+module_param(jiffies_till_sched_qs, ulong, 0444);
+static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
+module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
+
+/*
+ * Make sure that we give the grace-period kthread time to detect any
+ * idle CPUs before taking active measures to force quiescent states.
+ * However, don't go below 100 milliseconds, adjusted upwards for really
+ * large systems.
+ */
+static void adjust_jiffies_till_sched_qs(void)
+{
+ unsigned long j;
+
+ /* If jiffies_till_sched_qs was specified, respect the request. */
+ if (jiffies_till_sched_qs != ULONG_MAX) {
+ WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
+ return;
+ }
+ /* Otherwise, set to third fqs scan, but bound below on large system. */
+ j = READ_ONCE(jiffies_till_first_fqs) +
+ 2 * READ_ONCE(jiffies_till_next_fqs);
+ if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
+ j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
+ pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
+ WRITE_ONCE(jiffies_to_sched_qs, j);
+}
+
+static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
+{
+ ulong j;
+ int ret = kstrtoul(val, 0, &j);
+
+ if (!ret) {
+ WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
+ adjust_jiffies_till_sched_qs();
+ }
+ return ret;
+}
+
+static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
+{
+ ulong j;
+ int ret = kstrtoul(val, 0, &j);
+
+ if (!ret) {
+ WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
+ adjust_jiffies_till_sched_qs();
+ }
+ return ret;
+}
+
+static const struct kernel_param_ops first_fqs_jiffies_ops = {
+ .set = param_set_first_fqs_jiffies,
+ .get = param_get_ulong,
+};
+
+static const struct kernel_param_ops next_fqs_jiffies_ops = {
+ .set = param_set_next_fqs_jiffies,
+ .get = param_get_ulong,
+};
+
+module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
+module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
+module_param(rcu_kick_kthreads, bool, 0644);
+
+static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
+static int rcu_pending(int user);
+
+/*
+ * Return the number of RCU GPs completed thus far for debug & stats.
+ */
+unsigned long rcu_get_gp_seq(void)
+{
+ return READ_ONCE(rcu_state.gp_seq);
+}
+EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
+
+/*
+ * Return the number of RCU expedited batches completed thus far for
+ * debug & stats. Odd numbers mean that a batch is in progress, even
+ * numbers mean idle. The value returned will thus be roughly double
+ * the cumulative batches since boot.
+ */
+unsigned long rcu_exp_batches_completed(void)
+{
+ return rcu_state.expedited_sequence;
+}
+EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
+
+/*
+ * Return the root node of the rcu_state structure.
+ */
+static struct rcu_node *rcu_get_root(void)
+{
+ return &rcu_state.node[0];
+}
+
+/*
+ * Send along grace-period-related data for rcutorture diagnostics.
+ */
+void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
+ unsigned long *gp_seq)
+{
+ switch (test_type) {
+ case RCU_FLAVOR:
+ *flags = READ_ONCE(rcu_state.gp_flags);
+ *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
+ break;
+ default:
+ break;
+ }
+}
+EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
+
+#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
+/*
+ * An empty function that will trigger a reschedule on
+ * IRQ tail once IRQs get re-enabled on userspace/guest resume.
+ */
+static void late_wakeup_func(struct irq_work *work)
+{
+}
+
+static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
+ IRQ_WORK_INIT(late_wakeup_func);
+
+/*
+ * If either:
+ *
+ * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
+ * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
+ *
+ * In these cases the late RCU wake ups aren't supported in the resched loops and our
+ * last resort is to fire a local irq_work that will trigger a reschedule once IRQs
+ * get re-enabled again.
+ */
+noinstr void rcu_irq_work_resched(void)
+{
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+ if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
+ return;
+
+ if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
+ return;
+
+ instrumentation_begin();
+ if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
+ irq_work_queue(this_cpu_ptr(&late_wakeup_work));
+ }
+ instrumentation_end();
+}
+#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */
+
+#ifdef CONFIG_PROVE_RCU
+/**
+ * rcu_irq_exit_check_preempt - Validate that scheduling is possible
+ */
+void rcu_irq_exit_check_preempt(void)
+{
+ lockdep_assert_irqs_disabled();
+
+ RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0,
+ "RCU dynticks_nesting counter underflow/zero!");
+ RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() !=
+ DYNTICK_IRQ_NONIDLE,
+ "Bad RCU dynticks_nmi_nesting counter\n");
+ RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
+ "RCU in extended quiescent state!");
+}
+#endif /* #ifdef CONFIG_PROVE_RCU */
+
+#ifdef CONFIG_NO_HZ_FULL
+/**
+ * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
+ *
+ * The scheduler tick is not normally enabled when CPUs enter the kernel
+ * from nohz_full userspace execution. After all, nohz_full userspace
+ * execution is an RCU quiescent state and the time executing in the kernel
+ * is quite short. Except of course when it isn't. And it is not hard to
+ * cause a large system to spend tens of seconds or even minutes looping
+ * in the kernel, which can cause a number of problems, include RCU CPU
+ * stall warnings.
+ *
+ * Therefore, if a nohz_full CPU fails to report a quiescent state
+ * in a timely manner, the RCU grace-period kthread sets that CPU's
+ * ->rcu_urgent_qs flag with the expectation that the next interrupt or
+ * exception will invoke this function, which will turn on the scheduler
+ * tick, which will enable RCU to detect that CPU's quiescent states,
+ * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
+ * The tick will be disabled once a quiescent state is reported for
+ * this CPU.
+ *
+ * Of course, in carefully tuned systems, there might never be an
+ * interrupt or exception. In that case, the RCU grace-period kthread
+ * will eventually cause one to happen. However, in less carefully
+ * controlled environments, this function allows RCU to get what it
+ * needs without creating otherwise useless interruptions.
+ */
+void __rcu_irq_enter_check_tick(void)
+{
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+ // If we're here from NMI there's nothing to do.
+ if (in_nmi())
+ return;
+
+ RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
+ "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
+
+ if (!tick_nohz_full_cpu(rdp->cpu) ||
+ !READ_ONCE(rdp->rcu_urgent_qs) ||
+ READ_ONCE(rdp->rcu_forced_tick)) {
+ // RCU doesn't need nohz_full help from this CPU, or it is
+ // already getting that help.
+ return;
+ }
+
+ // We get here only when not in an extended quiescent state and
+ // from interrupts (as opposed to NMIs). Therefore, (1) RCU is
+ // already watching and (2) The fact that we are in an interrupt
+ // handler and that the rcu_node lock is an irq-disabled lock
+ // prevents self-deadlock. So we can safely recheck under the lock.
+ // Note that the nohz_full state currently cannot change.
+ raw_spin_lock_rcu_node(rdp->mynode);
+ if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
+ // A nohz_full CPU is in the kernel and RCU needs a
+ // quiescent state. Turn on the tick!
+ WRITE_ONCE(rdp->rcu_forced_tick, true);
+ tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
+ }
+ raw_spin_unlock_rcu_node(rdp->mynode);
+}
+NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick);
+#endif /* CONFIG_NO_HZ_FULL */
+
+/*
+ * Check to see if any future non-offloaded RCU-related work will need
+ * to be done by the current CPU, even if none need be done immediately,
+ * returning 1 if so. This function is part of the RCU implementation;
+ * it is -not- an exported member of the RCU API. This is used by
+ * the idle-entry code to figure out whether it is safe to disable the
+ * scheduler-clock interrupt.
+ *
+ * Just check whether or not this CPU has non-offloaded RCU callbacks
+ * queued.
+ */
+int rcu_needs_cpu(void)
+{
+ return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
+ !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
+}
+
+/*
+ * If any sort of urgency was applied to the current CPU (for example,
+ * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
+ * to get to a quiescent state, disable it.
+ */
+static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
+{
+ raw_lockdep_assert_held_rcu_node(rdp->mynode);
+ WRITE_ONCE(rdp->rcu_urgent_qs, false);
+ WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
+ if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
+ tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
+ WRITE_ONCE(rdp->rcu_forced_tick, false);
+ }
+}
+
+/**
+ * rcu_is_watching - RCU read-side critical sections permitted on current CPU?
+ *
+ * Return @true if RCU is watching the running CPU and @false otherwise.
+ * An @true return means that this CPU can safely enter RCU read-side
+ * critical sections.
+ *
+ * Although calls to rcu_is_watching() from most parts of the kernel
+ * will return @true, there are important exceptions. For example, if the
+ * current CPU is deep within its idle loop, in kernel entry/exit code,
+ * or offline, rcu_is_watching() will return @false.
+ *
+ * Make notrace because it can be called by the internal functions of
+ * ftrace, and making this notrace removes unnecessary recursion calls.
+ */
+notrace bool rcu_is_watching(void)
+{
+ bool ret;
+
+ preempt_disable_notrace();
+ ret = !rcu_dynticks_curr_cpu_in_eqs();
+ preempt_enable_notrace();
+ return ret;
+}
+EXPORT_SYMBOL_GPL(rcu_is_watching);
+
+/*
+ * If a holdout task is actually running, request an urgent quiescent
+ * state from its CPU. This is unsynchronized, so migrations can cause
+ * the request to go to the wrong CPU. Which is OK, all that will happen
+ * is that the CPU's next context switch will be a bit slower and next
+ * time around this task will generate another request.
+ */
+void rcu_request_urgent_qs_task(struct task_struct *t)
+{
+ int cpu;
+
+ barrier();
+ cpu = task_cpu(t);
+ if (!task_curr(t))
+ return; /* This task is not running on that CPU. */
+ smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
+}
+
+/*
+ * When trying to report a quiescent state on behalf of some other CPU,
+ * it is our responsibility to check for and handle potential overflow
+ * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
+ * After all, the CPU might be in deep idle state, and thus executing no
+ * code whatsoever.
+ */
+static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+ raw_lockdep_assert_held_rcu_node(rnp);
+ if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
+ rnp->gp_seq))
+ WRITE_ONCE(rdp->gpwrap, true);
+ if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
+ rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
+}
+
+/*
+ * Snapshot the specified CPU's dynticks counter so that we can later
+ * credit them with an implicit quiescent state. Return 1 if this CPU
+ * is in dynticks idle mode, which is an extended quiescent state.
+ */
+static int dyntick_save_progress_counter(struct rcu_data *rdp)
+{
+ rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
+ if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
+ trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
+ rcu_gpnum_ovf(rdp->mynode, rdp);
+ return 1;
+ }
+ return 0;
+}
+
+/*
+ * Returns positive if the specified CPU has passed through a quiescent state
+ * by virtue of being in or having passed through an dynticks idle state since
+ * the last call to dyntick_save_progress_counter() for this same CPU, or by
+ * virtue of having been offline.
+ *
+ * Returns negative if the specified CPU needs a force resched.
+ *
+ * Returns zero otherwise.
+ */
+static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
+{
+ unsigned long jtsq;
+ int ret = 0;
+ struct rcu_node *rnp = rdp->mynode;
+
+ /*
+ * If the CPU passed through or entered a dynticks idle phase with
+ * no active irq/NMI handlers, then we can safely pretend that the CPU
+ * already acknowledged the request to pass through a quiescent
+ * state. Either way, that CPU cannot possibly be in an RCU
+ * read-side critical section that started before the beginning
+ * of the current RCU grace period.
+ */
+ if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
+ trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
+ rcu_gpnum_ovf(rnp, rdp);
+ return 1;
+ }
+
+ /*
+ * Complain if a CPU that is considered to be offline from RCU's
+ * perspective has not yet reported a quiescent state. After all,
+ * the offline CPU should have reported a quiescent state during
+ * the CPU-offline process, or, failing that, by rcu_gp_init()
+ * if it ran concurrently with either the CPU going offline or the
+ * last task on a leaf rcu_node structure exiting its RCU read-side
+ * critical section while all CPUs corresponding to that structure
+ * are offline. This added warning detects bugs in any of these
+ * code paths.
+ *
+ * The rcu_node structure's ->lock is held here, which excludes
+ * the relevant portions the CPU-hotplug code, the grace-period
+ * initialization code, and the rcu_read_unlock() code paths.
+ *
+ * For more detail, please refer to the "Hotplug CPU" section
+ * of RCU's Requirements documentation.
+ */
+ if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
+ struct rcu_node *rnp1;
+
+ pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
+ __func__, rnp->grplo, rnp->grphi, rnp->level,
+ (long)rnp->gp_seq, (long)rnp->completedqs);
+ for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
+ pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
+ __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
+ pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
+ __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
+ (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
+ (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
+ return 1; /* Break things loose after complaining. */
+ }
+
+ /*
+ * A CPU running for an extended time within the kernel can
+ * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
+ * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
+ * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
+ * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
+ * variable are safe because the assignments are repeated if this
+ * CPU failed to pass through a quiescent state. This code
+ * also checks .jiffies_resched in case jiffies_to_sched_qs
+ * is set way high.
+ */
+ jtsq = READ_ONCE(jiffies_to_sched_qs);
+ if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
+ (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
+ time_after(jiffies, rcu_state.jiffies_resched) ||
+ rcu_state.cbovld)) {
+ WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
+ /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
+ smp_store_release(&rdp->rcu_urgent_qs, true);
+ } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
+ WRITE_ONCE(rdp->rcu_urgent_qs, true);
+ }
+
+ /*
+ * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
+ * The above code handles this, but only for straight cond_resched().
+ * And some in-kernel loops check need_resched() before calling
+ * cond_resched(), which defeats the above code for CPUs that are
+ * running in-kernel with scheduling-clock interrupts disabled.
+ * So hit them over the head with the resched_cpu() hammer!
+ */
+ if (tick_nohz_full_cpu(rdp->cpu) &&
+ (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
+ rcu_state.cbovld)) {
+ WRITE_ONCE(rdp->rcu_urgent_qs, true);
+ WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+ ret = -1;
+ }
+
+ /*
+ * If more than halfway to RCU CPU stall-warning time, invoke
+ * resched_cpu() more frequently to try to loosen things up a bit.
+ * Also check to see if the CPU is getting hammered with interrupts,
+ * but only once per grace period, just to keep the IPIs down to
+ * a dull roar.
+ */
+ if (time_after(jiffies, rcu_state.jiffies_resched)) {
+ if (time_after(jiffies,
+ READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
+ WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+ ret = -1;
+ }
+ if (IS_ENABLED(CONFIG_IRQ_WORK) &&
+ !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
+ (rnp->ffmask & rdp->grpmask)) {
+ rdp->rcu_iw_pending = true;
+ rdp->rcu_iw_gp_seq = rnp->gp_seq;
+ irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
+ }
+
+ if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) {
+ int cpu = rdp->cpu;
+ struct rcu_snap_record *rsrp;
+ struct kernel_cpustat *kcsp;
+
+ kcsp = &kcpustat_cpu(cpu);
+
+ rsrp = &rdp->snap_record;
+ rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
+ rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
+ rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
+ rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
+ rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu);
+ rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
+ rsrp->jiffies = jiffies;
+ rsrp->gp_seq = rdp->gp_seq;
+ }
+ }
+
+ return ret;
+}
+
+/* Trace-event wrapper function for trace_rcu_future_grace_period. */
+static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
+ unsigned long gp_seq_req, const char *s)
+{
+ trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
+ gp_seq_req, rnp->level,
+ rnp->grplo, rnp->grphi, s);
+}
+
+/*
+ * rcu_start_this_gp - Request the start of a particular grace period
+ * @rnp_start: The leaf node of the CPU from which to start.
+ * @rdp: The rcu_data corresponding to the CPU from which to start.
+ * @gp_seq_req: The gp_seq of the grace period to start.
+ *
+ * Start the specified grace period, as needed to handle newly arrived
+ * callbacks. The required future grace periods are recorded in each
+ * rcu_node structure's ->gp_seq_needed field. Returns true if there
+ * is reason to awaken the grace-period kthread.
+ *
+ * The caller must hold the specified rcu_node structure's ->lock, which
+ * is why the caller is responsible for waking the grace-period kthread.
+ *
+ * Returns true if the GP thread needs to be awakened else false.
+ */
+static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
+ unsigned long gp_seq_req)
+{
+ bool ret = false;
+ struct rcu_node *rnp;
+
+ /*
+ * Use funnel locking to either acquire the root rcu_node
+ * structure's lock or bail out if the need for this grace period
+ * has already been recorded -- or if that grace period has in
+ * fact already started. If there is already a grace period in
+ * progress in a non-leaf node, no recording is needed because the
+ * end of the grace period will scan the leaf rcu_node structures.
+ * Note that rnp_start->lock must not be released.
+ */
+ raw_lockdep_assert_held_rcu_node(rnp_start);
+ trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
+ for (rnp = rnp_start; 1; rnp = rnp->parent) {
+ if (rnp != rnp_start)
+ raw_spin_lock_rcu_node(rnp);
+ if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
+ rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
+ (rnp != rnp_start &&
+ rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
+ trace_rcu_this_gp(rnp, rdp, gp_seq_req,
+ TPS("Prestarted"));
+ goto unlock_out;
+ }
+ WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
+ if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
+ /*
+ * We just marked the leaf or internal node, and a
+ * grace period is in progress, which means that
+ * rcu_gp_cleanup() will see the marking. Bail to
+ * reduce contention.
+ */
+ trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
+ TPS("Startedleaf"));
+ goto unlock_out;
+ }
+ if (rnp != rnp_start && rnp->parent != NULL)
+ raw_spin_unlock_rcu_node(rnp);
+ if (!rnp->parent)
+ break; /* At root, and perhaps also leaf. */
+ }
+
+ /* If GP already in progress, just leave, otherwise start one. */
+ if (rcu_gp_in_progress()) {
+ trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
+ goto unlock_out;
+ }
+ trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
+ WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
+ WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
+ if (!READ_ONCE(rcu_state.gp_kthread)) {
+ trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
+ goto unlock_out;
+ }
+ trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
+ ret = true; /* Caller must wake GP kthread. */
+unlock_out:
+ /* Push furthest requested GP to leaf node and rcu_data structure. */
+ if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
+ WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
+ WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
+ }
+ if (rnp != rnp_start)
+ raw_spin_unlock_rcu_node(rnp);
+ return ret;
+}
+
+/*
+ * Clean up any old requests for the just-ended grace period. Also return
+ * whether any additional grace periods have been requested.
+ */
+static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
+{
+ bool needmore;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+ needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
+ if (!needmore)
+ rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
+ trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
+ needmore ? TPS("CleanupMore") : TPS("Cleanup"));
+ return needmore;
+}
+
+static void swake_up_one_online_ipi(void *arg)
+{
+ struct swait_queue_head *wqh = arg;
+
+ swake_up_one(wqh);
+}
+
+static void swake_up_one_online(struct swait_queue_head *wqh)
+{
+ int cpu = get_cpu();
+
+ /*
+ * If called from rcutree_report_cpu_starting(), wake up
+ * is dangerous that late in the CPU-down hotplug process. The
+ * scheduler might queue an ignored hrtimer. Defer the wake up
+ * to an online CPU instead.
+ */
+ if (unlikely(cpu_is_offline(cpu))) {
+ int target;
+
+ target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU),
+ cpu_online_mask);
+
+ smp_call_function_single(target, swake_up_one_online_ipi,
+ wqh, 0);
+ put_cpu();
+ } else {
+ put_cpu();
+ swake_up_one(wqh);
+ }
+}
+
+/*
+ * Awaken the grace-period kthread. Don't do a self-awaken (unless in an
+ * interrupt or softirq handler, in which case we just might immediately
+ * sleep upon return, resulting in a grace-period hang), and don't bother
+ * awakening when there is nothing for the grace-period kthread to do
+ * (as in several CPUs raced to awaken, we lost), and finally don't try
+ * to awaken a kthread that has not yet been created. If all those checks
+ * are passed, track some debug information and awaken.
+ *
+ * So why do the self-wakeup when in an interrupt or softirq handler
+ * in the grace-period kthread's context? Because the kthread might have
+ * been interrupted just as it was going to sleep, and just after the final
+ * pre-sleep check of the awaken condition. In this case, a wakeup really
+ * is required, and is therefore supplied.
+ */
+static void rcu_gp_kthread_wake(void)
+{
+ struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
+
+ if ((current == t && !in_hardirq() && !in_serving_softirq()) ||
+ !READ_ONCE(rcu_state.gp_flags) || !t)
+ return;
+ WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
+ WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
+ swake_up_one_online(&rcu_state.gp_wq);
+}
+
+/*
+ * If there is room, assign a ->gp_seq number to any callbacks on this
+ * CPU that have not already been assigned. Also accelerate any callbacks
+ * that were previously assigned a ->gp_seq number that has since proven
+ * to be too conservative, which can happen if callbacks get assigned a
+ * ->gp_seq number while RCU is idle, but with reference to a non-root
+ * rcu_node structure. This function is idempotent, so it does not hurt
+ * to call it repeatedly. Returns an flag saying that we should awaken
+ * the RCU grace-period kthread.
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+ unsigned long gp_seq_req;
+ bool ret = false;
+
+ rcu_lockdep_assert_cblist_protected(rdp);
+ raw_lockdep_assert_held_rcu_node(rnp);
+
+ /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+ if (!rcu_segcblist_pend_cbs(&rdp->cblist))
+ return false;
+
+ trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
+
+ /*
+ * Callbacks are often registered with incomplete grace-period
+ * information. Something about the fact that getting exact
+ * information requires acquiring a global lock... RCU therefore
+ * makes a conservative estimate of the grace period number at which
+ * a given callback will become ready to invoke. The following
+ * code checks this estimate and improves it when possible, thus
+ * accelerating callback invocation to an earlier grace-period
+ * number.
+ */
+ gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
+ if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
+ ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
+
+ /* Trace depending on how much we were able to accelerate. */
+ if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
+ trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
+ else
+ trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
+
+ trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
+
+ return ret;
+}
+
+/*
+ * Similar to rcu_accelerate_cbs(), but does not require that the leaf
+ * rcu_node structure's ->lock be held. It consults the cached value
+ * of ->gp_seq_needed in the rcu_data structure, and if that indicates
+ * that a new grace-period request be made, invokes rcu_accelerate_cbs()
+ * while holding the leaf rcu_node structure's ->lock.
+ */
+static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
+ struct rcu_data *rdp)
+{
+ unsigned long c;
+ bool needwake;
+
+ rcu_lockdep_assert_cblist_protected(rdp);
+ c = rcu_seq_snap(&rcu_state.gp_seq);
+ if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
+ /* Old request still live, so mark recent callbacks. */
+ (void)rcu_segcblist_accelerate(&rdp->cblist, c);
+ return;
+ }
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+ needwake = rcu_accelerate_cbs(rnp, rdp);
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ if (needwake)
+ rcu_gp_kthread_wake();
+}
+
+/*
+ * Move any callbacks whose grace period has completed to the
+ * RCU_DONE_TAIL sublist, then compact the remaining sublists and
+ * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
+ * sublist. This function is idempotent, so it does not hurt to
+ * invoke it repeatedly. As long as it is not invoked -too- often...
+ * Returns true if the RCU grace-period kthread needs to be awakened.
+ *
+ * The caller must hold rnp->lock with interrupts disabled.
+ */
+static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+ rcu_lockdep_assert_cblist_protected(rdp);
+ raw_lockdep_assert_held_rcu_node(rnp);
+
+ /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
+ if (!rcu_segcblist_pend_cbs(&rdp->cblist))
+ return false;
+
+ /*
+ * Find all callbacks whose ->gp_seq numbers indicate that they
+ * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
+ */
+ rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
+
+ /* Classify any remaining callbacks. */
+ return rcu_accelerate_cbs(rnp, rdp);
+}
+
+/*
+ * Move and classify callbacks, but only if doing so won't require
+ * that the RCU grace-period kthread be awakened.
+ */
+static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
+ struct rcu_data *rdp)
+{
+ rcu_lockdep_assert_cblist_protected(rdp);
+ if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
+ return;
+ // The grace period cannot end while we hold the rcu_node lock.
+ if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
+ WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
+ raw_spin_unlock_rcu_node(rnp);
+}
+
+/*
+ * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
+ * quiescent state. This is intended to be invoked when the CPU notices
+ * a new grace period.
+ */
+static void rcu_strict_gp_check_qs(void)
+{
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
+ rcu_read_lock();
+ rcu_read_unlock();
+ }
+}
+
+/*
+ * Update CPU-local rcu_data state to record the beginnings and ends of
+ * grace periods. The caller must hold the ->lock of the leaf rcu_node
+ * structure corresponding to the current CPU, and must have irqs disabled.
+ * Returns true if the grace-period kthread needs to be awakened.
+ */
+static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
+{
+ bool ret = false;
+ bool need_qs;
+ const bool offloaded = rcu_rdp_is_offloaded(rdp);
+
+ raw_lockdep_assert_held_rcu_node(rnp);
+
+ if (rdp->gp_seq == rnp->gp_seq)
+ return false; /* Nothing to do. */
+
+ /* Handle the ends of any preceding grace periods first. */
+ if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
+ unlikely(READ_ONCE(rdp->gpwrap))) {
+ if (!offloaded)
+ ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
+ rdp->core_needs_qs = false;
+ trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
+ } else {
+ if (!offloaded)
+ ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
+ if (rdp->core_needs_qs)
+ rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
+ }
+
+ /* Now handle the beginnings of any new-to-this-CPU grace periods. */
+ if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
+ unlikely(READ_ONCE(rdp->gpwrap))) {
+ /*
+ * If the current grace period is waiting for this CPU,
+ * set up to detect a quiescent state, otherwise don't
+ * go looking for one.
+ */
+ trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
+ need_qs = !!(rnp->qsmask & rdp->grpmask);
+ rdp->cpu_no_qs.b.norm = need_qs;
+ rdp->core_needs_qs = need_qs;
+ zero_cpu_stall_ticks(rdp);
+ }
+ rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
+ if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
+ WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
+ if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
+ WRITE_ONCE(rdp->last_sched_clock, jiffies);
+ WRITE_ONCE(rdp->gpwrap, false);
+ rcu_gpnum_ovf(rnp, rdp);
+ return ret;
+}
+
+static void note_gp_changes(struct rcu_data *rdp)
+{
+ unsigned long flags;
+ bool needwake;
+ struct rcu_node *rnp;
+
+ local_irq_save(flags);
+ rnp = rdp->mynode;
+ if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
+ !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
+ !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
+ local_irq_restore(flags);
+ return;
+ }
+ needwake = __note_gp_changes(rnp, rdp);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ rcu_strict_gp_check_qs();
+ if (needwake)
+ rcu_gp_kthread_wake();
+}
+
+static atomic_t *rcu_gp_slow_suppress;
+
+/* Register a counter to suppress debugging grace-period delays. */
+void rcu_gp_slow_register(atomic_t *rgssp)
+{
+ WARN_ON_ONCE(rcu_gp_slow_suppress);
+
+ WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
+
+/* Unregister a counter, with NULL for not caring which. */
+void rcu_gp_slow_unregister(atomic_t *rgssp)
+{
+ WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
+
+ WRITE_ONCE(rcu_gp_slow_suppress, NULL);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
+
+static bool rcu_gp_slow_is_suppressed(void)
+{
+ atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
+
+ return rgssp && atomic_read(rgssp);
+}
+
+static void rcu_gp_slow(int delay)
+{
+ if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
+ !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
+ schedule_timeout_idle(delay);
+}
+
+static unsigned long sleep_duration;
+
+/* Allow rcutorture to stall the grace-period kthread. */
+void rcu_gp_set_torture_wait(int duration)
+{
+ if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
+ WRITE_ONCE(sleep_duration, duration);
+}
+EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
+
+/* Actually implement the aforementioned wait. */
+static void rcu_gp_torture_wait(void)
+{
+ unsigned long duration;
+
+ if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
+ return;
+ duration = xchg(&sleep_duration, 0UL);
+ if (duration > 0) {
+ pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
+ schedule_timeout_idle(duration);
+ pr_alert("%s: Wait complete\n", __func__);
+ }
+}
+
+/*
+ * Handler for on_each_cpu() to invoke the target CPU's RCU core
+ * processing.
+ */
+static void rcu_strict_gp_boundary(void *unused)
+{
+ invoke_rcu_core();
+}
+
+// Make the polled API aware of the beginning of a grace period.
+static void rcu_poll_gp_seq_start(unsigned long *snap)
+{
+ struct rcu_node *rnp = rcu_get_root();
+
+ if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
+ raw_lockdep_assert_held_rcu_node(rnp);
+
+ // If RCU was idle, note beginning of GP.
+ if (!rcu_seq_state(rcu_state.gp_seq_polled))
+ rcu_seq_start(&rcu_state.gp_seq_polled);
+
+ // Either way, record current state.
+ *snap = rcu_state.gp_seq_polled;
+}
+
+// Make the polled API aware of the end of a grace period.
+static void rcu_poll_gp_seq_end(unsigned long *snap)
+{
+ struct rcu_node *rnp = rcu_get_root();
+
+ if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
+ raw_lockdep_assert_held_rcu_node(rnp);
+
+ // If the previously noted GP is still in effect, record the
+ // end of that GP. Either way, zero counter to avoid counter-wrap
+ // problems.
+ if (*snap && *snap == rcu_state.gp_seq_polled) {
+ rcu_seq_end(&rcu_state.gp_seq_polled);
+ rcu_state.gp_seq_polled_snap = 0;
+ rcu_state.gp_seq_polled_exp_snap = 0;
+ } else {
+ *snap = 0;
+ }
+}
+
+// Make the polled API aware of the beginning of a grace period, but
+// where caller does not hold the root rcu_node structure's lock.
+static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
+{
+ unsigned long flags;
+ struct rcu_node *rnp = rcu_get_root();
+
+ if (rcu_init_invoked()) {
+ if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
+ lockdep_assert_irqs_enabled();
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ }
+ rcu_poll_gp_seq_start(snap);
+ if (rcu_init_invoked())
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
+// Make the polled API aware of the end of a grace period, but where
+// caller does not hold the root rcu_node structure's lock.
+static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
+{
+ unsigned long flags;
+ struct rcu_node *rnp = rcu_get_root();
+
+ if (rcu_init_invoked()) {
+ if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
+ lockdep_assert_irqs_enabled();
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ }
+ rcu_poll_gp_seq_end(snap);
+ if (rcu_init_invoked())
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
+/*
+ * Initialize a new grace period. Return false if no grace period required.
+ */
+static noinline_for_stack bool rcu_gp_init(void)
+{
+ unsigned long flags;
+ unsigned long oldmask;
+ unsigned long mask;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp = rcu_get_root();
+
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ raw_spin_lock_irq_rcu_node(rnp);
+ if (!READ_ONCE(rcu_state.gp_flags)) {
+ /* Spurious wakeup, tell caller to go back to sleep. */
+ raw_spin_unlock_irq_rcu_node(rnp);
+ return false;
+ }
+ WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
+
+ if (WARN_ON_ONCE(rcu_gp_in_progress())) {
+ /*
+ * Grace period already in progress, don't start another.
+ * Not supposed to be able to happen.
+ */
+ raw_spin_unlock_irq_rcu_node(rnp);
+ return false;
+ }
+
+ /* Advance to a new grace period and initialize state. */
+ record_gp_stall_check_time();
+ /* Record GP times before starting GP, hence rcu_seq_start(). */
+ rcu_seq_start(&rcu_state.gp_seq);
+ ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
+ rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
+ raw_spin_unlock_irq_rcu_node(rnp);
+
+ /*
+ * Apply per-leaf buffered online and offline operations to
+ * the rcu_node tree. Note that this new grace period need not
+ * wait for subsequent online CPUs, and that RCU hooks in the CPU
+ * offlining path, when combined with checks in this function,
+ * will handle CPUs that are currently going offline or that will
+ * go offline later. Please also refer to "Hotplug CPU" section
+ * of RCU's Requirements documentation.
+ */
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
+ /* Exclude CPU hotplug operations. */
+ rcu_for_each_leaf_node(rnp) {
+ local_irq_save(flags);
+ arch_spin_lock(&rcu_state.ofl_lock);
+ raw_spin_lock_rcu_node(rnp);
+ if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
+ !rnp->wait_blkd_tasks) {
+ /* Nothing to do on this leaf rcu_node structure. */
+ raw_spin_unlock_rcu_node(rnp);
+ arch_spin_unlock(&rcu_state.ofl_lock);
+ local_irq_restore(flags);
+ continue;
+ }
+
+ /* Record old state, apply changes to ->qsmaskinit field. */
+ oldmask = rnp->qsmaskinit;
+ rnp->qsmaskinit = rnp->qsmaskinitnext;
+
+ /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
+ if (!oldmask != !rnp->qsmaskinit) {
+ if (!oldmask) { /* First online CPU for rcu_node. */
+ if (!rnp->wait_blkd_tasks) /* Ever offline? */
+ rcu_init_new_rnp(rnp);
+ } else if (rcu_preempt_has_tasks(rnp)) {
+ rnp->wait_blkd_tasks = true; /* blocked tasks */
+ } else { /* Last offline CPU and can propagate. */
+ rcu_cleanup_dead_rnp(rnp);
+ }
+ }
+
+ /*
+ * If all waited-on tasks from prior grace period are
+ * done, and if all this rcu_node structure's CPUs are
+ * still offline, propagate up the rcu_node tree and
+ * clear ->wait_blkd_tasks. Otherwise, if one of this
+ * rcu_node structure's CPUs has since come back online,
+ * simply clear ->wait_blkd_tasks.
+ */
+ if (rnp->wait_blkd_tasks &&
+ (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
+ rnp->wait_blkd_tasks = false;
+ if (!rnp->qsmaskinit)
+ rcu_cleanup_dead_rnp(rnp);
+ }
+
+ raw_spin_unlock_rcu_node(rnp);
+ arch_spin_unlock(&rcu_state.ofl_lock);
+ local_irq_restore(flags);
+ }
+ rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
+
+ /*
+ * Set the quiescent-state-needed bits in all the rcu_node
+ * structures for all currently online CPUs in breadth-first
+ * order, starting from the root rcu_node structure, relying on the
+ * layout of the tree within the rcu_state.node[] array. Note that
+ * other CPUs will access only the leaves of the hierarchy, thus
+ * seeing that no grace period is in progress, at least until the
+ * corresponding leaf node has been initialized.
+ *
+ * The grace period cannot complete until the initialization
+ * process finishes, because this kthread handles both.
+ */
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
+ rcu_for_each_node_breadth_first(rnp) {
+ rcu_gp_slow(gp_init_delay);
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rdp = this_cpu_ptr(&rcu_data);
+ rcu_preempt_check_blocked_tasks(rnp);
+ rnp->qsmask = rnp->qsmaskinit;
+ WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
+ if (rnp == rdp->mynode)
+ (void)__note_gp_changes(rnp, rdp);
+ rcu_preempt_boost_start_gp(rnp);
+ trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
+ rnp->level, rnp->grplo,
+ rnp->grphi, rnp->qsmask);
+ /* Quiescent states for tasks on any now-offline CPUs. */
+ mask = rnp->qsmask & ~rnp->qsmaskinitnext;
+ rnp->rcu_gp_init_mask = mask;
+ if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
+ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
+ else
+ raw_spin_unlock_irq_rcu_node(rnp);
+ cond_resched_tasks_rcu_qs();
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ }
+
+ // If strict, make all CPUs aware of new grace period.
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
+
+ return true;
+}
+
+/*
+ * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
+ * time.
+ */
+static bool rcu_gp_fqs_check_wake(int *gfp)
+{
+ struct rcu_node *rnp = rcu_get_root();
+
+ // If under overload conditions, force an immediate FQS scan.
+ if (*gfp & RCU_GP_FLAG_OVLD)
+ return true;
+
+ // Someone like call_rcu() requested a force-quiescent-state scan.
+ *gfp = READ_ONCE(rcu_state.gp_flags);
+ if (*gfp & RCU_GP_FLAG_FQS)
+ return true;
+
+ // The current grace period has completed.
+ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
+ return true;
+
+ return false;
+}
+
+/*
+ * Do one round of quiescent-state forcing.
+ */
+static void rcu_gp_fqs(bool first_time)
+{
+ int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall);
+ struct rcu_node *rnp = rcu_get_root();
+
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
+
+ WARN_ON_ONCE(nr_fqs > 3);
+ /* Only countdown nr_fqs for stall purposes if jiffies moves. */
+ if (nr_fqs) {
+ if (nr_fqs == 1) {
+ WRITE_ONCE(rcu_state.jiffies_stall,
+ jiffies + rcu_jiffies_till_stall_check());
+ }
+ WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs);
+ }
+
+ if (first_time) {
+ /* Collect dyntick-idle snapshots. */
+ force_qs_rnp(dyntick_save_progress_counter);
+ } else {
+ /* Handle dyntick-idle and offline CPUs. */
+ force_qs_rnp(rcu_implicit_dynticks_qs);
+ }
+ /* Clear flag to prevent immediate re-entry. */
+ if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
+ raw_spin_lock_irq_rcu_node(rnp);
+ WRITE_ONCE(rcu_state.gp_flags,
+ READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
+ raw_spin_unlock_irq_rcu_node(rnp);
+ }
+}
+
+/*
+ * Loop doing repeated quiescent-state forcing until the grace period ends.
+ */
+static noinline_for_stack void rcu_gp_fqs_loop(void)
+{
+ bool first_gp_fqs = true;
+ int gf = 0;
+ unsigned long j;
+ int ret;
+ struct rcu_node *rnp = rcu_get_root();
+
+ j = READ_ONCE(jiffies_till_first_fqs);
+ if (rcu_state.cbovld)
+ gf = RCU_GP_FLAG_OVLD;
+ ret = 0;
+ for (;;) {
+ if (rcu_state.cbovld) {
+ j = (j + 2) / 3;
+ if (j <= 0)
+ j = 1;
+ }
+ if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) {
+ WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
+ /*
+ * jiffies_force_qs before RCU_GP_WAIT_FQS state
+ * update; required for stall checks.
+ */
+ smp_wmb();
+ WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
+ jiffies + (j ? 3 * j : 2));
+ }
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
+ TPS("fqswait"));
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
+ (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
+ rcu_gp_fqs_check_wake(&gf), j);
+ rcu_gp_torture_wait();
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
+ /* Locking provides needed memory barriers. */
+ /*
+ * Exit the loop if the root rcu_node structure indicates that the grace period
+ * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check
+ * is required only for single-node rcu_node trees because readers blocking
+ * the current grace period are queued only on leaf rcu_node structures.
+ * For multi-node trees, checking the root node's ->qsmask suffices, because a
+ * given root node's ->qsmask bit is cleared only when all CPUs and tasks from
+ * the corresponding leaf nodes have passed through their quiescent state.
+ */
+ if (!READ_ONCE(rnp->qsmask) &&
+ !rcu_preempt_blocked_readers_cgp(rnp))
+ break;
+ /* If time for quiescent-state forcing, do it. */
+ if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
+ (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
+ TPS("fqsstart"));
+ rcu_gp_fqs(first_gp_fqs);
+ gf = 0;
+ if (first_gp_fqs) {
+ first_gp_fqs = false;
+ gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
+ }
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
+ TPS("fqsend"));
+ cond_resched_tasks_rcu_qs();
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ ret = 0; /* Force full wait till next FQS. */
+ j = READ_ONCE(jiffies_till_next_fqs);
+ } else {
+ /* Deal with stray signal. */
+ cond_resched_tasks_rcu_qs();
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ WARN_ON(signal_pending(current));
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
+ TPS("fqswaitsig"));
+ ret = 1; /* Keep old FQS timing. */
+ j = jiffies;
+ if (time_after(jiffies, rcu_state.jiffies_force_qs))
+ j = 1;
+ else
+ j = rcu_state.jiffies_force_qs - j;
+ gf = 0;
+ }
+ }
+}
+
+/*
+ * Clean up after the old grace period.
+ */
+static noinline void rcu_gp_cleanup(void)
+{
+ int cpu;
+ bool needgp = false;
+ unsigned long gp_duration;
+ unsigned long new_gp_seq;
+ bool offloaded;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp = rcu_get_root();
+ struct swait_queue_head *sq;
+
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ raw_spin_lock_irq_rcu_node(rnp);
+ rcu_state.gp_end = jiffies;
+ gp_duration = rcu_state.gp_end - rcu_state.gp_start;
+ if (gp_duration > rcu_state.gp_max)
+ rcu_state.gp_max = gp_duration;
+
+ /*
+ * We know the grace period is complete, but to everyone else
+ * it appears to still be ongoing. But it is also the case
+ * that to everyone else it looks like there is nothing that
+ * they can do to advance the grace period. It is therefore
+ * safe for us to drop the lock in order to mark the grace
+ * period as completed in all of the rcu_node structures.
+ */
+ rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap);
+ raw_spin_unlock_irq_rcu_node(rnp);
+
+ /*
+ * Propagate new ->gp_seq value to rcu_node structures so that
+ * other CPUs don't have to wait until the start of the next grace
+ * period to process their callbacks. This also avoids some nasty
+ * RCU grace-period initialization races by forcing the end of
+ * the current grace period to be completely recorded in all of
+ * the rcu_node structures before the beginning of the next grace
+ * period is recorded in any of the rcu_node structures.
+ */
+ new_gp_seq = rcu_state.gp_seq;
+ rcu_seq_end(&new_gp_seq);
+ rcu_for_each_node_breadth_first(rnp) {
+ raw_spin_lock_irq_rcu_node(rnp);
+ if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
+ dump_blkd_tasks(rnp, 10);
+ WARN_ON_ONCE(rnp->qsmask);
+ WRITE_ONCE(rnp->gp_seq, new_gp_seq);
+ if (!rnp->parent)
+ smp_mb(); // Order against failing poll_state_synchronize_rcu_full().
+ rdp = this_cpu_ptr(&rcu_data);
+ if (rnp == rdp->mynode)
+ needgp = __note_gp_changes(rnp, rdp) || needgp;
+ /* smp_mb() provided by prior unlock-lock pair. */
+ needgp = rcu_future_gp_cleanup(rnp) || needgp;
+ // Reset overload indication for CPUs no longer overloaded
+ if (rcu_is_leaf_node(rnp))
+ for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ check_cb_ovld_locked(rdp, rnp);
+ }
+ sq = rcu_nocb_gp_get(rnp);
+ raw_spin_unlock_irq_rcu_node(rnp);
+ rcu_nocb_gp_cleanup(sq);
+ cond_resched_tasks_rcu_qs();
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ rcu_gp_slow(gp_cleanup_delay);
+ }
+ rnp = rcu_get_root();
+ raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
+
+ /* Declare grace period done, trace first to use old GP number. */
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
+ rcu_seq_end(&rcu_state.gp_seq);
+ ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
+ /* Check for GP requests since above loop. */
+ rdp = this_cpu_ptr(&rcu_data);
+ if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
+ trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
+ TPS("CleanupMore"));
+ needgp = true;
+ }
+ /* Advance CBs to reduce false positives below. */
+ offloaded = rcu_rdp_is_offloaded(rdp);
+ if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
+
+ // We get here if a grace period was needed (“needgp”)
+ // and the above call to rcu_accelerate_cbs() did not set
+ // the RCU_GP_FLAG_INIT bit in ->gp_state (which records
+ // the need for another grace period).  The purpose
+ // of the “offloaded” check is to avoid invoking
+ // rcu_accelerate_cbs() on an offloaded CPU because we do not
+ // hold the ->nocb_lock needed to safely access an offloaded
+ // ->cblist.  We do not want to acquire that lock because
+ // it can be heavily contended during callback floods.
+
+ WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
+ WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
+ } else {
+
+ // We get here either if there is no need for an
+ // additional grace period or if rcu_accelerate_cbs() has
+ // already set the RCU_GP_FLAG_INIT bit in ->gp_flags. 
+ // So all we need to do is to clear all of the other
+ // ->gp_flags bits.
+
+ WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
+ }
+ raw_spin_unlock_irq_rcu_node(rnp);
+
+ // If strict, make all CPUs aware of the end of the old grace period.
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
+}
+
+/*
+ * Body of kthread that handles grace periods.
+ */
+static int __noreturn rcu_gp_kthread(void *unused)
+{
+ rcu_bind_gp_kthread();
+ for (;;) {
+
+ /* Handle grace-period start. */
+ for (;;) {
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
+ TPS("reqwait"));
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
+ swait_event_idle_exclusive(rcu_state.gp_wq,
+ READ_ONCE(rcu_state.gp_flags) &
+ RCU_GP_FLAG_INIT);
+ rcu_gp_torture_wait();
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
+ /* Locking provides needed memory barrier. */
+ if (rcu_gp_init())
+ break;
+ cond_resched_tasks_rcu_qs();
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ WARN_ON(signal_pending(current));
+ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
+ TPS("reqwaitsig"));
+ }
+
+ /* Handle quiescent-state forcing. */
+ rcu_gp_fqs_loop();
+
+ /* Handle grace-period end. */
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
+ rcu_gp_cleanup();
+ WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
+ }
+}
+
+/*
+ * Report a full set of quiescent states to the rcu_state data structure.
+ * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
+ * another grace period is required. Whether we wake the grace-period
+ * kthread or it awakens itself for the next round of quiescent-state
+ * forcing, that kthread will clean up after the just-completed grace
+ * period. Note that the caller must hold rnp->lock, which is released
+ * before return.
+ */
+static void rcu_report_qs_rsp(unsigned long flags)
+ __releases(rcu_get_root()->lock)
+{
+ raw_lockdep_assert_held_rcu_node(rcu_get_root());
+ WARN_ON_ONCE(!rcu_gp_in_progress());
+ WRITE_ONCE(rcu_state.gp_flags,
+ READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
+ raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
+ rcu_gp_kthread_wake();
+}
+
+/*
+ * Similar to rcu_report_qs_rdp(), for which it is a helper function.
+ * Allows quiescent states for a group of CPUs to be reported at one go
+ * to the specified rcu_node structure, though all the CPUs in the group
+ * must be represented by the same rcu_node structure (which need not be a
+ * leaf rcu_node structure, though it often will be). The gps parameter
+ * is the grace-period snapshot, which means that the quiescent states
+ * are valid only if rnp->gp_seq is equal to gps. That structure's lock
+ * must be held upon entry, and it is released before return.
+ *
+ * As a special case, if mask is zero, the bit-already-cleared check is
+ * disabled. This allows propagating quiescent state due to resumed tasks
+ * during grace-period initialization.
+ */
+static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
+ unsigned long gps, unsigned long flags)
+ __releases(rnp->lock)
+{
+ unsigned long oldmask = 0;
+ struct rcu_node *rnp_c;
+
+ raw_lockdep_assert_held_rcu_node(rnp);
+
+ /* Walk up the rcu_node hierarchy. */
+ for (;;) {
+ if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
+
+ /*
+ * Our bit has already been cleared, or the
+ * relevant grace period is already over, so done.
+ */
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
+ WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
+ rcu_preempt_blocked_readers_cgp(rnp));
+ WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
+ trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
+ mask, rnp->qsmask, rnp->level,
+ rnp->grplo, rnp->grphi,
+ !!rnp->gp_tasks);
+ if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
+
+ /* Other bits still set at this level, so done. */
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ rnp->completedqs = rnp->gp_seq;
+ mask = rnp->grpmask;
+ if (rnp->parent == NULL) {
+
+ /* No more levels. Exit loop holding root lock. */
+
+ break;
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ rnp_c = rnp;
+ rnp = rnp->parent;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ oldmask = READ_ONCE(rnp_c->qsmask);
+ }
+
+ /*
+ * Get here if we are the last CPU to pass through a quiescent
+ * state for this grace period. Invoke rcu_report_qs_rsp()
+ * to clean up and start the next grace period if one is needed.
+ */
+ rcu_report_qs_rsp(flags); /* releases rnp->lock. */
+}
+
+/*
+ * Record a quiescent state for all tasks that were previously queued
+ * on the specified rcu_node structure and that were blocking the current
+ * RCU grace period. The caller must hold the corresponding rnp->lock with
+ * irqs disabled, and this lock is released upon return, but irqs remain
+ * disabled.
+ */
+static void __maybe_unused
+rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ unsigned long gps;
+ unsigned long mask;
+ struct rcu_node *rnp_p;
+
+ raw_lockdep_assert_held_rcu_node(rnp);
+ if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
+ WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
+ rnp->qsmask != 0) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return; /* Still need more quiescent states! */
+ }
+
+ rnp->completedqs = rnp->gp_seq;
+ rnp_p = rnp->parent;
+ if (rnp_p == NULL) {
+ /*
+ * Only one rcu_node structure in the tree, so don't
+ * try to report up to its nonexistent parent!
+ */
+ rcu_report_qs_rsp(flags);
+ return;
+ }
+
+ /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
+ gps = rnp->gp_seq;
+ mask = rnp->grpmask;
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
+ rcu_report_qs_rnp(mask, rnp_p, gps, flags);
+}
+
+/*
+ * Record a quiescent state for the specified CPU to that CPU's rcu_data
+ * structure. This must be called from the specified CPU.
+ */
+static void
+rcu_report_qs_rdp(struct rcu_data *rdp)
+{
+ unsigned long flags;
+ unsigned long mask;
+ bool needacc = false;
+ struct rcu_node *rnp;
+
+ WARN_ON_ONCE(rdp->cpu != smp_processor_id());
+ rnp = rdp->mynode;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
+ rdp->gpwrap) {
+
+ /*
+ * The grace period in which this quiescent state was
+ * recorded has ended, so don't report it upwards.
+ * We will instead need a new quiescent state that lies
+ * within the current grace period.
+ */
+ rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ mask = rdp->grpmask;
+ rdp->core_needs_qs = false;
+ if ((rnp->qsmask & mask) == 0) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ } else {
+ /*
+ * This GP can't end until cpu checks in, so all of our
+ * callbacks can be processed during the next GP.
+ *
+ * NOCB kthreads have their own way to deal with that...
+ */
+ if (!rcu_rdp_is_offloaded(rdp)) {
+ /*
+ * The current GP has not yet ended, so it
+ * should not be possible for rcu_accelerate_cbs()
+ * to return true. So complain, but don't awaken.
+ */
+ WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
+ } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
+ /*
+ * ...but NOCB kthreads may miss or delay callbacks acceleration
+ * if in the middle of a (de-)offloading process.
+ */
+ needacc = true;
+ }
+
+ rcu_disable_urgency_upon_qs(rdp);
+ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
+ /* ^^^ Released rnp->lock */
+
+ if (needacc) {
+ rcu_nocb_lock_irqsave(rdp, flags);
+ rcu_accelerate_cbs_unlocked(rnp, rdp);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ }
+ }
+}
+
+/*
+ * Check to see if there is a new grace period of which this CPU
+ * is not yet aware, and if so, set up local rcu_data state for it.
+ * Otherwise, see if this CPU has just passed through its first
+ * quiescent state for this grace period, and record that fact if so.
+ */
+static void
+rcu_check_quiescent_state(struct rcu_data *rdp)
+{
+ /* Check for grace-period ends and beginnings. */
+ note_gp_changes(rdp);
+
+ /*
+ * Does this CPU still need to do its part for current grace period?
+ * If no, return and let the other CPUs do their part as well.
+ */
+ if (!rdp->core_needs_qs)
+ return;
+
+ /*
+ * Was there a quiescent state since the beginning of the grace
+ * period? If no, then exit and wait for the next call.
+ */
+ if (rdp->cpu_no_qs.b.norm)
+ return;
+
+ /*
+ * Tell RCU we are done (but rcu_report_qs_rdp() will be the
+ * judge of that).
+ */
+ rcu_report_qs_rdp(rdp);
+}
+
+/* Return true if callback-invocation time limit exceeded. */
+static bool rcu_do_batch_check_time(long count, long tlimit,
+ bool jlimit_check, unsigned long jlimit)
+{
+ // Invoke local_clock() only once per 32 consecutive callbacks.
+ return unlikely(tlimit) &&
+ (!likely(count & 31) ||
+ (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) &&
+ jlimit_check && time_after(jiffies, jlimit))) &&
+ local_clock() >= tlimit;
+}
+
+/*
+ * Invoke any RCU callbacks that have made it to the end of their grace
+ * period. Throttle as specified by rdp->blimit.
+ */
+static void rcu_do_batch(struct rcu_data *rdp)
+{
+ long bl;
+ long count = 0;
+ int div;
+ bool __maybe_unused empty;
+ unsigned long flags;
+ unsigned long jlimit;
+ bool jlimit_check = false;
+ long pending;
+ struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
+ struct rcu_head *rhp;
+ long tlimit = 0;
+
+ /* If no callbacks are ready, just return. */
+ if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
+ trace_rcu_batch_start(rcu_state.name,
+ rcu_segcblist_n_cbs(&rdp->cblist), 0);
+ trace_rcu_batch_end(rcu_state.name, 0,
+ !rcu_segcblist_empty(&rdp->cblist),
+ need_resched(), is_idle_task(current),
+ rcu_is_callbacks_kthread(rdp));
+ return;
+ }
+
+ /*
+ * Extract the list of ready callbacks, disabling IRQs to prevent
+ * races with call_rcu() from interrupt handlers. Leave the
+ * callback counts, as rcu_barrier() needs to be conservative.
+ */
+ rcu_nocb_lock_irqsave(rdp, flags);
+ WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
+ pending = rcu_segcblist_get_seglen(&rdp->cblist, RCU_DONE_TAIL);
+ div = READ_ONCE(rcu_divisor);
+ div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
+ bl = max(rdp->blimit, pending >> div);
+ if ((in_serving_softirq() || rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING) &&
+ (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) || unlikely(bl > 100))) {
+ const long npj = NSEC_PER_SEC / HZ;
+ long rrn = READ_ONCE(rcu_resched_ns);
+
+ rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
+ tlimit = local_clock() + rrn;
+ jlimit = jiffies + (rrn + npj + 1) / npj;
+ jlimit_check = true;
+ }
+ trace_rcu_batch_start(rcu_state.name,
+ rcu_segcblist_n_cbs(&rdp->cblist), bl);
+ rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
+ if (rcu_rdp_is_offloaded(rdp))
+ rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
+
+ trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+
+ /* Invoke callbacks. */
+ tick_dep_set_task(current, TICK_DEP_BIT_RCU);
+ rhp = rcu_cblist_dequeue(&rcl);
+
+ for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+ rcu_callback_t f;
+
+ count++;
+ debug_rcu_head_unqueue(rhp);
+
+ rcu_lock_acquire(&rcu_callback_map);
+ trace_rcu_invoke_callback(rcu_state.name, rhp);
+
+ f = rhp->func;
+ WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
+ f(rhp);
+
+ rcu_lock_release(&rcu_callback_map);
+
+ /*
+ * Stop only if limit reached and CPU has something to do.
+ */
+ if (in_serving_softirq()) {
+ if (count >= bl && (need_resched() || !is_idle_task(current)))
+ break;
+ /*
+ * Make sure we don't spend too much time here and deprive other
+ * softirq vectors of CPU cycles.
+ */
+ if (rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit))
+ break;
+ } else {
+ // In rcuc/rcuoc context, so no worries about
+ // depriving other softirq vectors of CPU cycles.
+ local_bh_enable();
+ lockdep_assert_irqs_enabled();
+ cond_resched_tasks_rcu_qs();
+ lockdep_assert_irqs_enabled();
+ local_bh_disable();
+ // But rcuc kthreads can delay quiescent-state
+ // reporting, so check time limits for them.
+ if (rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING &&
+ rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) {
+ rdp->rcu_cpu_has_work = 1;
+ break;
+ }
+ }
+ }
+
+ rcu_nocb_lock_irqsave(rdp, flags);
+ rdp->n_cbs_invoked += count;
+ trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
+ is_idle_task(current), rcu_is_callbacks_kthread(rdp));
+
+ /* Update counts and requeue any remaining callbacks. */
+ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
+ rcu_segcblist_add_len(&rdp->cblist, -count);
+
+ /* Reinstate batch limit if we have worked down the excess. */
+ count = rcu_segcblist_n_cbs(&rdp->cblist);
+ if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
+ rdp->blimit = blimit;
+
+ /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
+ if (count == 0 && rdp->qlen_last_fqs_check != 0) {
+ rdp->qlen_last_fqs_check = 0;
+ rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
+ } else if (count < rdp->qlen_last_fqs_check - qhimark)
+ rdp->qlen_last_fqs_check = count;
+
+ /*
+ * The following usually indicates a double call_rcu(). To track
+ * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
+ */
+ empty = rcu_segcblist_empty(&rdp->cblist);
+ WARN_ON_ONCE(count == 0 && !empty);
+ WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
+ count != 0 && empty);
+ WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
+ WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
+
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+
+ tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
+}
+
+/*
+ * This function is invoked from each scheduling-clock interrupt,
+ * and checks to see if this CPU is in a non-context-switch quiescent
+ * state, for example, user mode or idle loop. It also schedules RCU
+ * core processing. If the current grace period has gone on too long,
+ * it will ask the scheduler to manufacture a context switch for the sole
+ * purpose of providing the needed quiescent state.
+ */
+void rcu_sched_clock_irq(int user)
+{
+ unsigned long j;
+
+ if (IS_ENABLED(CONFIG_PROVE_RCU)) {
+ j = jiffies;
+ WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
+ __this_cpu_write(rcu_data.last_sched_clock, j);
+ }
+ trace_rcu_utilization(TPS("Start scheduler-tick"));
+ lockdep_assert_irqs_disabled();
+ raw_cpu_inc(rcu_data.ticks_this_gp);
+ /* The load-acquire pairs with the store-release setting to true. */
+ if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
+ /* Idle and userspace execution already are quiescent states. */
+ if (!rcu_is_cpu_rrupt_from_idle() && !user) {
+ set_tsk_need_resched(current);
+ set_preempt_need_resched();
+ }
+ __this_cpu_write(rcu_data.rcu_urgent_qs, false);
+ }
+ rcu_flavor_sched_clock_irq(user);
+ if (rcu_pending(user))
+ invoke_rcu_core();
+ if (user || rcu_is_cpu_rrupt_from_idle())
+ rcu_note_voluntary_context_switch(current);
+ lockdep_assert_irqs_disabled();
+
+ trace_rcu_utilization(TPS("End scheduler-tick"));
+}
+
+/*
+ * Scan the leaf rcu_node structures. For each structure on which all
+ * CPUs have reported a quiescent state and on which there are tasks
+ * blocking the current grace period, initiate RCU priority boosting.
+ * Otherwise, invoke the specified function to check dyntick state for
+ * each CPU that has not yet reported a quiescent state.
+ */
+static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
+{
+ int cpu;
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ rcu_state.cbovld = rcu_state.cbovldnext;
+ rcu_state.cbovldnext = false;
+ rcu_for_each_leaf_node(rnp) {
+ unsigned long mask = 0;
+ unsigned long rsmask = 0;
+
+ cond_resched_tasks_rcu_qs();
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rcu_state.cbovldnext |= !!rnp->cbovldmask;
+ if (rnp->qsmask == 0) {
+ if (rcu_preempt_blocked_readers_cgp(rnp)) {
+ /*
+ * No point in scanning bits because they
+ * are all zero. But we might need to
+ * priority-boost blocked readers.
+ */
+ rcu_initiate_boost(rnp, flags);
+ /* rcu_initiate_boost() releases rnp->lock */
+ continue;
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ continue;
+ }
+ for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
+ struct rcu_data *rdp;
+ int ret;
+
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ ret = f(rdp);
+ if (ret > 0) {
+ mask |= rdp->grpmask;
+ rcu_disable_urgency_upon_qs(rdp);
+ }
+ if (ret < 0)
+ rsmask |= rdp->grpmask;
+ }
+ if (mask != 0) {
+ /* Idle/offline CPUs, report (releases rnp->lock). */
+ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
+ } else {
+ /* Nothing to do here, so just drop the lock. */
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+
+ for_each_leaf_node_cpu_mask(rnp, cpu, rsmask)
+ resched_cpu(cpu);
+ }
+}
+
+/*
+ * Force quiescent states on reluctant CPUs, and also detect which
+ * CPUs are in dyntick-idle mode.
+ */
+void rcu_force_quiescent_state(void)
+{
+ unsigned long flags;
+ bool ret;
+ struct rcu_node *rnp;
+ struct rcu_node *rnp_old = NULL;
+
+ /* Funnel through hierarchy to reduce memory contention. */
+ rnp = raw_cpu_read(rcu_data.mynode);
+ for (; rnp != NULL; rnp = rnp->parent) {
+ ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
+ !raw_spin_trylock(&rnp->fqslock);
+ if (rnp_old != NULL)
+ raw_spin_unlock(&rnp_old->fqslock);
+ if (ret)
+ return;
+ rnp_old = rnp;
+ }
+ /* rnp_old == rcu_get_root(), rnp == NULL. */
+
+ /* Reached the root of the rcu_node tree, acquire lock. */
+ raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
+ raw_spin_unlock(&rnp_old->fqslock);
+ if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
+ return; /* Someone beat us to it. */
+ }
+ WRITE_ONCE(rcu_state.gp_flags,
+ READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
+ raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
+ rcu_gp_kthread_wake();
+}
+EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
+
+// Workqueue handler for an RCU reader for kernels enforcing struct RCU
+// grace periods.
+static void strict_work_handler(struct work_struct *work)
+{
+ rcu_read_lock();
+ rcu_read_unlock();
+}
+
+/* Perform RCU core processing work for the current CPU. */
+static __latent_entropy void rcu_core(void)
+{
+ unsigned long flags;
+ struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
+ struct rcu_node *rnp = rdp->mynode;
+ /*
+ * On RT rcu_core() can be preempted when IRQs aren't disabled.
+ * Therefore this function can race with concurrent NOCB (de-)offloading
+ * on this CPU and the below condition must be considered volatile.
+ * However if we race with:
+ *
+ * _ Offloading: In the worst case we accelerate or process callbacks
+ * concurrently with NOCB kthreads. We are guaranteed to
+ * call rcu_nocb_lock() if that happens.
+ *
+ * _ Deoffloading: In the worst case we miss callbacks acceleration or
+ * processing. This is fine because the early stage
+ * of deoffloading invokes rcu_core() after setting
+ * SEGCBLIST_RCU_CORE. So we guarantee that we'll process
+ * what could have been dismissed without the need to wait
+ * for the next rcu_pending() check in the next jiffy.
+ */
+ const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
+
+ if (cpu_is_offline(smp_processor_id()))
+ return;
+ trace_rcu_utilization(TPS("Start RCU core"));
+ WARN_ON_ONCE(!rdp->beenonline);
+
+ /* Report any deferred quiescent states if preemption enabled. */
+ if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
+ rcu_preempt_deferred_qs(current);
+ } else if (rcu_preempt_need_deferred_qs(current)) {
+ set_tsk_need_resched(current);
+ set_preempt_need_resched();
+ }
+
+ /* Update RCU state based on any recent quiescent states. */
+ rcu_check_quiescent_state(rdp);
+
+ /* No grace period and unregistered callbacks? */
+ if (!rcu_gp_in_progress() &&
+ rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
+ rcu_nocb_lock_irqsave(rdp, flags);
+ if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
+ rcu_accelerate_cbs_unlocked(rnp, rdp);
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ }
+
+ rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
+
+ /* If there are callbacks ready, invoke them. */
+ if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
+ likely(READ_ONCE(rcu_scheduler_fully_active))) {
+ rcu_do_batch(rdp);
+ /* Re-invoke RCU core processing if there are callbacks remaining. */
+ if (rcu_segcblist_ready_cbs(&rdp->cblist))
+ invoke_rcu_core();
+ }
+
+ /* Do any needed deferred wakeups of rcuo kthreads. */
+ do_nocb_deferred_wakeup(rdp);
+ trace_rcu_utilization(TPS("End RCU core"));
+
+ // If strict GPs, schedule an RCU reader in a clean environment.
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
+}
+
+static void rcu_core_si(struct softirq_action *h)
+{
+ rcu_core();
+}
+
+static void rcu_wake_cond(struct task_struct *t, int status)
+{
+ /*
+ * If the thread is yielding, only wake it when this
+ * is invoked from idle
+ */
+ if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
+ wake_up_process(t);
+}
+
+static void invoke_rcu_core_kthread(void)
+{
+ struct task_struct *t;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
+ t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
+ if (t != NULL && t != current)
+ rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
+ local_irq_restore(flags);
+}
+
+/*
+ * Wake up this CPU's rcuc kthread to do RCU core processing.
+ */
+static void invoke_rcu_core(void)
+{
+ if (!cpu_online(smp_processor_id()))
+ return;
+ if (use_softirq)
+ raise_softirq(RCU_SOFTIRQ);
+ else
+ invoke_rcu_core_kthread();
+}
+
+static void rcu_cpu_kthread_park(unsigned int cpu)
+{
+ per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
+}
+
+static int rcu_cpu_kthread_should_run(unsigned int cpu)
+{
+ return __this_cpu_read(rcu_data.rcu_cpu_has_work);
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks. This replaces
+ * the RCU softirq used in configurations of RCU that do not support RCU
+ * priority boosting.
+ */
+static void rcu_cpu_kthread(unsigned int cpu)
+{
+ unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
+ char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
+ unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity);
+ int spincnt;
+
+ trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
+ for (spincnt = 0; spincnt < 10; spincnt++) {
+ WRITE_ONCE(*j, jiffies);
+ local_bh_disable();
+ *statusp = RCU_KTHREAD_RUNNING;
+ local_irq_disable();
+ work = *workp;
+ WRITE_ONCE(*workp, 0);
+ local_irq_enable();
+ if (work)
+ rcu_core();
+ local_bh_enable();
+ if (!READ_ONCE(*workp)) {
+ trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
+ *statusp = RCU_KTHREAD_WAITING;
+ return;
+ }
+ }
+ *statusp = RCU_KTHREAD_YIELDING;
+ trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
+ schedule_timeout_idle(2);
+ trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
+ *statusp = RCU_KTHREAD_WAITING;
+ WRITE_ONCE(*j, jiffies);
+}
+
+static struct smp_hotplug_thread rcu_cpu_thread_spec = {
+ .store = &rcu_data.rcu_cpu_kthread_task,
+ .thread_should_run = rcu_cpu_kthread_should_run,
+ .thread_fn = rcu_cpu_kthread,
+ .thread_comm = "rcuc/%u",
+ .setup = rcu_cpu_kthread_setup,
+ .park = rcu_cpu_kthread_park,
+};
+
+/*
+ * Spawn per-CPU RCU core processing kthreads.
+ */
+static int __init rcu_spawn_core_kthreads(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
+ if (use_softirq)
+ return 0;
+ WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
+ "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
+ return 0;
+}
+
+/*
+ * Handle any core-RCU processing required by a call_rcu() invocation.
+ */
+static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
+ unsigned long flags)
+{
+ /*
+ * If called from an extended quiescent state, invoke the RCU
+ * core in order to force a re-evaluation of RCU's idleness.
+ */
+ if (!rcu_is_watching())
+ invoke_rcu_core();
+
+ /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
+ if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
+ return;
+
+ /*
+ * Force the grace period if too many callbacks or too long waiting.
+ * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
+ * if some other CPU has recently done so. Also, don't bother
+ * invoking rcu_force_quiescent_state() if the newly enqueued callback
+ * is the only one waiting for a grace period to complete.
+ */
+ if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
+ rdp->qlen_last_fqs_check + qhimark)) {
+
+ /* Are we ignoring a completed grace period? */
+ note_gp_changes(rdp);
+
+ /* Start a new grace period if one not already started. */
+ if (!rcu_gp_in_progress()) {
+ rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
+ } else {
+ /* Give the grace period a kick. */
+ rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
+ if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
+ rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
+ rcu_force_quiescent_state();
+ rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
+ rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
+ }
+ }
+}
+
+/*
+ * RCU callback function to leak a callback.
+ */
+static void rcu_leak_callback(struct rcu_head *rhp)
+{
+}
+
+/*
+ * Check and if necessary update the leaf rcu_node structure's
+ * ->cbovldmask bit corresponding to the current CPU based on that CPU's
+ * number of queued RCU callbacks. The caller must hold the leaf rcu_node
+ * structure's ->lock.
+ */
+static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
+{
+ raw_lockdep_assert_held_rcu_node(rnp);
+ if (qovld_calc <= 0)
+ return; // Early boot and wildcard value set.
+ if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
+ WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
+ else
+ WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
+}
+
+/*
+ * Check and if necessary update the leaf rcu_node structure's
+ * ->cbovldmask bit corresponding to the current CPU based on that CPU's
+ * number of queued RCU callbacks. No locks need be held, but the
+ * caller must have disabled interrupts.
+ *
+ * Note that this function ignores the possibility that there are a lot
+ * of callbacks all of which have already seen the end of their respective
+ * grace periods. This omission is due to the need for no-CBs CPUs to
+ * be holding ->nocb_lock to do this check, which is too heavy for a
+ * common-case operation.
+ */
+static void check_cb_ovld(struct rcu_data *rdp)
+{
+ struct rcu_node *const rnp = rdp->mynode;
+
+ if (qovld_calc <= 0 ||
+ ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
+ !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
+ return; // Early boot wildcard value or already set correctly.
+ raw_spin_lock_rcu_node(rnp);
+ check_cb_ovld_locked(rdp, rnp);
+ raw_spin_unlock_rcu_node(rnp);
+}
+
+static void
+__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
+{
+ static atomic_t doublefrees;
+ unsigned long flags;
+ bool lazy;
+ struct rcu_data *rdp;
+ bool was_alldone;
+
+ /* Misaligned rcu_head! */
+ WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
+
+ if (debug_rcu_head_queue(head)) {
+ /*
+ * Probable double call_rcu(), so leak the callback.
+ * Use rcu:rcu_callback trace event to find the previous
+ * time callback was passed to call_rcu().
+ */
+ if (atomic_inc_return(&doublefrees) < 4) {
+ pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
+ mem_dump_obj(head);
+ }
+ WRITE_ONCE(head->func, rcu_leak_callback);
+ return;
+ }
+ head->func = func;
+ head->next = NULL;
+ kasan_record_aux_stack_noalloc(head);
+ local_irq_save(flags);
+ rdp = this_cpu_ptr(&rcu_data);
+ lazy = lazy_in && !rcu_async_should_hurry();
+
+ /* Add the callback to our list. */
+ if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
+ // This can trigger due to call_rcu() from offline CPU:
+ WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
+ WARN_ON_ONCE(!rcu_is_watching());
+ // Very early boot, before rcu_init(). Initialize if needed
+ // and then drop through to queue the callback.
+ if (rcu_segcblist_empty(&rdp->cblist))
+ rcu_segcblist_init(&rdp->cblist);
+ }
+
+ check_cb_ovld(rdp);
+ if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
+ return; // Enqueued onto ->nocb_bypass, so just leave.
+ // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
+ rcu_segcblist_enqueue(&rdp->cblist, head);
+ if (__is_kvfree_rcu_offset((unsigned long)func))
+ trace_rcu_kvfree_callback(rcu_state.name, head,
+ (unsigned long)func,
+ rcu_segcblist_n_cbs(&rdp->cblist));
+ else
+ trace_rcu_callback(rcu_state.name, head,
+ rcu_segcblist_n_cbs(&rdp->cblist));
+
+ trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
+
+ /* Go handle any RCU core processing required. */
+ if (unlikely(rcu_rdp_is_offloaded(rdp))) {
+ __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
+ } else {
+ __call_rcu_core(rdp, head, flags);
+ local_irq_restore(flags);
+ }
+}
+
+#ifdef CONFIG_RCU_LAZY
+/**
+ * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
+ * flush all lazy callbacks (including the new one) to the main ->cblist while
+ * doing so.
+ *
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed.
+ *
+ * Use this API instead of call_rcu() if you don't want the callback to be
+ * invoked after very long periods of time, which can happen on systems without
+ * memory pressure and on systems which are lightly loaded or mostly idle.
+ * This function will cause callbacks to be invoked sooner than later at the
+ * expense of extra power. Other than that, this function is identical to, and
+ * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory
+ * ordering and other functionality.
+ */
+void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
+{
+ return __call_rcu_common(head, func, false);
+}
+EXPORT_SYMBOL_GPL(call_rcu_hurry);
+#endif
+
+/**
+ * call_rcu() - Queue an RCU callback for invocation after a grace period.
+ * By default the callbacks are 'lazy' and are kept hidden from the main
+ * ->cblist to prevent starting of grace periods too soon.
+ * If you desire grace periods to start very soon, use call_rcu_hurry().
+ *
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual callback function to be invoked after the grace period
+ *
+ * The callback function will be invoked some time after a full grace
+ * period elapses, in other words after all pre-existing RCU read-side
+ * critical sections have completed. However, the callback function
+ * might well execute concurrently with RCU read-side critical sections
+ * that started after call_rcu() was invoked.
+ *
+ * RCU read-side critical sections are delimited by rcu_read_lock()
+ * and rcu_read_unlock(), and may be nested. In addition, but only in
+ * v5.0 and later, regions of code across which interrupts, preemption,
+ * or softirqs have been disabled also serve as RCU read-side critical
+ * sections. This includes hardware interrupt handlers, softirq handlers,
+ * and NMI handlers.
+ *
+ * Note that all CPUs must agree that the grace period extended beyond
+ * all pre-existing RCU read-side critical section. On systems with more
+ * than one CPU, this means that when "func()" is invoked, each CPU is
+ * guaranteed to have executed a full memory barrier since the end of its
+ * last RCU read-side critical section whose beginning preceded the call
+ * to call_rcu(). It also means that each CPU executing an RCU read-side
+ * critical section that continues beyond the start of "func()" must have
+ * executed a memory barrier after the call_rcu() but before the beginning
+ * of that RCU read-side critical section. Note that these guarantees
+ * include CPUs that are offline, idle, or executing in user mode, as
+ * well as CPUs that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
+ * resulting RCU callback function "func()", then both CPU A and CPU B are
+ * guaranteed to execute a full memory barrier during the time interval
+ * between the call to call_rcu() and the invocation of "func()" -- even
+ * if CPU A and CPU B are the same CPU (but again only if the system has
+ * more than one CPU).
+ *
+ * Implementation of these memory-ordering guarantees is described here:
+ * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
+ */
+void call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+ return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
+}
+EXPORT_SYMBOL_GPL(call_rcu);
+
+/* Maximum number of jiffies to wait before draining a batch. */
+#define KFREE_DRAIN_JIFFIES (5 * HZ)
+#define KFREE_N_BATCHES 2
+#define FREE_N_CHANNELS 2
+
+/**
+ * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
+ * @list: List node. All blocks are linked between each other
+ * @gp_snap: Snapshot of RCU state for objects placed to this bulk
+ * @nr_records: Number of active pointers in the array
+ * @records: Array of the kvfree_rcu() pointers
+ */
+struct kvfree_rcu_bulk_data {
+ struct list_head list;
+ struct rcu_gp_oldstate gp_snap;
+ unsigned long nr_records;
+ void *records[];
+};
+
+/*
+ * This macro defines how many entries the "records" array
+ * will contain. It is based on the fact that the size of
+ * kvfree_rcu_bulk_data structure becomes exactly one page.
+ */
+#define KVFREE_BULK_MAX_ENTR \
+ ((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
+
+/**
+ * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
+ * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
+ * @head_free: List of kfree_rcu() objects waiting for a grace period
+ * @head_free_gp_snap: Grace-period snapshot to check for attempted premature frees.
+ * @bulk_head_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
+ * @krcp: Pointer to @kfree_rcu_cpu structure
+ */
+
+struct kfree_rcu_cpu_work {
+ struct rcu_work rcu_work;
+ struct rcu_head *head_free;
+ struct rcu_gp_oldstate head_free_gp_snap;
+ struct list_head bulk_head_free[FREE_N_CHANNELS];
+ struct kfree_rcu_cpu *krcp;
+};
+
+/**
+ * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
+ * @head: List of kfree_rcu() objects not yet waiting for a grace period
+ * @head_gp_snap: Snapshot of RCU state for objects placed to "@head"
+ * @bulk_head: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
+ * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
+ * @lock: Synchronize access to this structure
+ * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
+ * @initialized: The @rcu_work fields have been initialized
+ * @head_count: Number of objects in rcu_head singular list
+ * @bulk_count: Number of objects in bulk-list
+ * @bkvcache:
+ * A simple cache list that contains objects for reuse purpose.
+ * In order to save some per-cpu space the list is singular.
+ * Even though it is lockless an access has to be protected by the
+ * per-cpu lock.
+ * @page_cache_work: A work to refill the cache when it is empty
+ * @backoff_page_cache_fill: Delay cache refills
+ * @work_in_progress: Indicates that page_cache_work is running
+ * @hrtimer: A hrtimer for scheduling a page_cache_work
+ * @nr_bkv_objs: number of allocated objects at @bkvcache.
+ *
+ * This is a per-CPU structure. The reason that it is not included in
+ * the rcu_data structure is to permit this code to be extracted from
+ * the RCU files. Such extraction could allow further optimization of
+ * the interactions with the slab allocators.
+ */
+struct kfree_rcu_cpu {
+ // Objects queued on a linked list
+ // through their rcu_head structures.
+ struct rcu_head *head;
+ unsigned long head_gp_snap;
+ atomic_t head_count;
+
+ // Objects queued on a bulk-list.
+ struct list_head bulk_head[FREE_N_CHANNELS];
+ atomic_t bulk_count[FREE_N_CHANNELS];
+
+ struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
+ raw_spinlock_t lock;
+ struct delayed_work monitor_work;
+ bool initialized;
+
+ struct delayed_work page_cache_work;
+ atomic_t backoff_page_cache_fill;
+ atomic_t work_in_progress;
+ struct hrtimer hrtimer;
+
+ struct llist_head bkvcache;
+ int nr_bkv_objs;
+};
+
+static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
+ .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
+};
+
+static __always_inline void
+debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
+{
+#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
+ int i;
+
+ for (i = 0; i < bhead->nr_records; i++)
+ debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
+#endif
+}
+
+static inline struct kfree_rcu_cpu *
+krc_this_cpu_lock(unsigned long *flags)
+{
+ struct kfree_rcu_cpu *krcp;
+
+ local_irq_save(*flags); // For safely calling this_cpu_ptr().
+ krcp = this_cpu_ptr(&krc);
+ raw_spin_lock(&krcp->lock);
+
+ return krcp;
+}
+
+static inline void
+krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
+{
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+}
+
+static inline struct kvfree_rcu_bulk_data *
+get_cached_bnode(struct kfree_rcu_cpu *krcp)
+{
+ if (!krcp->nr_bkv_objs)
+ return NULL;
+
+ WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
+ return (struct kvfree_rcu_bulk_data *)
+ llist_del_first(&krcp->bkvcache);
+}
+
+static inline bool
+put_cached_bnode(struct kfree_rcu_cpu *krcp,
+ struct kvfree_rcu_bulk_data *bnode)
+{
+ // Check the limit.
+ if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
+ return false;
+
+ llist_add((struct llist_node *) bnode, &krcp->bkvcache);
+ WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
+ return true;
+}
+
+static int
+drain_page_cache(struct kfree_rcu_cpu *krcp)
+{
+ unsigned long flags;
+ struct llist_node *page_list, *pos, *n;
+ int freed = 0;
+
+ if (!rcu_min_cached_objs)
+ return 0;
+
+ raw_spin_lock_irqsave(&krcp->lock, flags);
+ page_list = llist_del_all(&krcp->bkvcache);
+ WRITE_ONCE(krcp->nr_bkv_objs, 0);
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+
+ llist_for_each_safe(pos, n, page_list) {
+ free_page((unsigned long)pos);
+ freed++;
+ }
+
+ return freed;
+}
+
+static void
+kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp,
+ struct kvfree_rcu_bulk_data *bnode, int idx)
+{
+ unsigned long flags;
+ int i;
+
+ if (!WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&bnode->gp_snap))) {
+ debug_rcu_bhead_unqueue(bnode);
+ rcu_lock_acquire(&rcu_callback_map);
+ if (idx == 0) { // kmalloc() / kfree().
+ trace_rcu_invoke_kfree_bulk_callback(
+ rcu_state.name, bnode->nr_records,
+ bnode->records);
+
+ kfree_bulk(bnode->nr_records, bnode->records);
+ } else { // vmalloc() / vfree().
+ for (i = 0; i < bnode->nr_records; i++) {
+ trace_rcu_invoke_kvfree_callback(
+ rcu_state.name, bnode->records[i], 0);
+
+ vfree(bnode->records[i]);
+ }
+ }
+ rcu_lock_release(&rcu_callback_map);
+ }
+
+ raw_spin_lock_irqsave(&krcp->lock, flags);
+ if (put_cached_bnode(krcp, bnode))
+ bnode = NULL;
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+
+ if (bnode)
+ free_page((unsigned long) bnode);
+
+ cond_resched_tasks_rcu_qs();
+}
+
+static void
+kvfree_rcu_list(struct rcu_head *head)
+{
+ struct rcu_head *next;
+
+ for (; head; head = next) {
+ void *ptr = (void *) head->func;
+ unsigned long offset = (void *) head - ptr;
+
+ next = head->next;
+ debug_rcu_head_unqueue((struct rcu_head *)ptr);
+ rcu_lock_acquire(&rcu_callback_map);
+ trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
+
+ if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
+ kvfree(ptr);
+
+ rcu_lock_release(&rcu_callback_map);
+ cond_resched_tasks_rcu_qs();
+ }
+}
+
+/*
+ * This function is invoked in workqueue context after a grace period.
+ * It frees all the objects queued on ->bulk_head_free or ->head_free.
+ */
+static void kfree_rcu_work(struct work_struct *work)
+{
+ unsigned long flags;
+ struct kvfree_rcu_bulk_data *bnode, *n;
+ struct list_head bulk_head[FREE_N_CHANNELS];
+ struct rcu_head *head;
+ struct kfree_rcu_cpu *krcp;
+ struct kfree_rcu_cpu_work *krwp;
+ struct rcu_gp_oldstate head_gp_snap;
+ int i;
+
+ krwp = container_of(to_rcu_work(work),
+ struct kfree_rcu_cpu_work, rcu_work);
+ krcp = krwp->krcp;
+
+ raw_spin_lock_irqsave(&krcp->lock, flags);
+ // Channels 1 and 2.
+ for (i = 0; i < FREE_N_CHANNELS; i++)
+ list_replace_init(&krwp->bulk_head_free[i], &bulk_head[i]);
+
+ // Channel 3.
+ head = krwp->head_free;
+ krwp->head_free = NULL;
+ head_gp_snap = krwp->head_free_gp_snap;
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+
+ // Handle the first two channels.
+ for (i = 0; i < FREE_N_CHANNELS; i++) {
+ // Start from the tail page, so a GP is likely passed for it.
+ list_for_each_entry_safe(bnode, n, &bulk_head[i], list)
+ kvfree_rcu_bulk(krcp, bnode, i);
+ }
+
+ /*
+ * This is used when the "bulk" path can not be used for the
+ * double-argument of kvfree_rcu(). This happens when the
+ * page-cache is empty, which means that objects are instead
+ * queued on a linked list through their rcu_head structures.
+ * This list is named "Channel 3".
+ */
+ if (head && !WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&head_gp_snap)))
+ kvfree_rcu_list(head);
+}
+
+static bool
+need_offload_krc(struct kfree_rcu_cpu *krcp)
+{
+ int i;
+
+ for (i = 0; i < FREE_N_CHANNELS; i++)
+ if (!list_empty(&krcp->bulk_head[i]))
+ return true;
+
+ return !!READ_ONCE(krcp->head);
+}
+
+static bool
+need_wait_for_krwp_work(struct kfree_rcu_cpu_work *krwp)
+{
+ int i;
+
+ for (i = 0; i < FREE_N_CHANNELS; i++)
+ if (!list_empty(&krwp->bulk_head_free[i]))
+ return true;
+
+ return !!krwp->head_free;
+}
+
+static int krc_count(struct kfree_rcu_cpu *krcp)
+{
+ int sum = atomic_read(&krcp->head_count);
+ int i;
+
+ for (i = 0; i < FREE_N_CHANNELS; i++)
+ sum += atomic_read(&krcp->bulk_count[i]);
+
+ return sum;
+}
+
+static void
+schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
+{
+ long delay, delay_left;
+
+ delay = krc_count(krcp) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES;
+ if (delayed_work_pending(&krcp->monitor_work)) {
+ delay_left = krcp->monitor_work.timer.expires - jiffies;
+ if (delay < delay_left)
+ mod_delayed_work(system_wq, &krcp->monitor_work, delay);
+ return;
+ }
+ queue_delayed_work(system_wq, &krcp->monitor_work, delay);
+}
+
+static void
+kvfree_rcu_drain_ready(struct kfree_rcu_cpu *krcp)
+{
+ struct list_head bulk_ready[FREE_N_CHANNELS];
+ struct kvfree_rcu_bulk_data *bnode, *n;
+ struct rcu_head *head_ready = NULL;
+ unsigned long flags;
+ int i;
+
+ raw_spin_lock_irqsave(&krcp->lock, flags);
+ for (i = 0; i < FREE_N_CHANNELS; i++) {
+ INIT_LIST_HEAD(&bulk_ready[i]);
+
+ list_for_each_entry_safe_reverse(bnode, n, &krcp->bulk_head[i], list) {
+ if (!poll_state_synchronize_rcu_full(&bnode->gp_snap))
+ break;
+
+ atomic_sub(bnode->nr_records, &krcp->bulk_count[i]);
+ list_move(&bnode->list, &bulk_ready[i]);
+ }
+ }
+
+ if (krcp->head && poll_state_synchronize_rcu(krcp->head_gp_snap)) {
+ head_ready = krcp->head;
+ atomic_set(&krcp->head_count, 0);
+ WRITE_ONCE(krcp->head, NULL);
+ }
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+
+ for (i = 0; i < FREE_N_CHANNELS; i++) {
+ list_for_each_entry_safe(bnode, n, &bulk_ready[i], list)
+ kvfree_rcu_bulk(krcp, bnode, i);
+ }
+
+ if (head_ready)
+ kvfree_rcu_list(head_ready);
+}
+
+/*
+ * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
+ */
+static void kfree_rcu_monitor(struct work_struct *work)
+{
+ struct kfree_rcu_cpu *krcp = container_of(work,
+ struct kfree_rcu_cpu, monitor_work.work);
+ unsigned long flags;
+ int i, j;
+
+ // Drain ready for reclaim.
+ kvfree_rcu_drain_ready(krcp);
+
+ raw_spin_lock_irqsave(&krcp->lock, flags);
+
+ // Attempt to start a new batch.
+ for (i = 0; i < KFREE_N_BATCHES; i++) {
+ struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
+
+ // Try to detach bulk_head or head and attach it, only when
+ // all channels are free. Any channel is not free means at krwp
+ // there is on-going rcu work to handle krwp's free business.
+ if (need_wait_for_krwp_work(krwp))
+ continue;
+
+ // kvfree_rcu_drain_ready() might handle this krcp, if so give up.
+ if (need_offload_krc(krcp)) {
+ // Channel 1 corresponds to the SLAB-pointer bulk path.
+ // Channel 2 corresponds to vmalloc-pointer bulk path.
+ for (j = 0; j < FREE_N_CHANNELS; j++) {
+ if (list_empty(&krwp->bulk_head_free[j])) {
+ atomic_set(&krcp->bulk_count[j], 0);
+ list_replace_init(&krcp->bulk_head[j],
+ &krwp->bulk_head_free[j]);
+ }
+ }
+
+ // Channel 3 corresponds to both SLAB and vmalloc
+ // objects queued on the linked list.
+ if (!krwp->head_free) {
+ krwp->head_free = krcp->head;
+ get_state_synchronize_rcu_full(&krwp->head_free_gp_snap);
+ atomic_set(&krcp->head_count, 0);
+ WRITE_ONCE(krcp->head, NULL);
+ }
+
+ // One work is per one batch, so there are three
+ // "free channels", the batch can handle. It can
+ // be that the work is in the pending state when
+ // channels have been detached following by each
+ // other.
+ queue_rcu_work(system_wq, &krwp->rcu_work);
+ }
+ }
+
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+
+ // If there is nothing to detach, it means that our job is
+ // successfully done here. In case of having at least one
+ // of the channels that is still busy we should rearm the
+ // work to repeat an attempt. Because previous batches are
+ // still in progress.
+ if (need_offload_krc(krcp))
+ schedule_delayed_monitor_work(krcp);
+}
+
+static enum hrtimer_restart
+schedule_page_work_fn(struct hrtimer *t)
+{
+ struct kfree_rcu_cpu *krcp =
+ container_of(t, struct kfree_rcu_cpu, hrtimer);
+
+ queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
+ return HRTIMER_NORESTART;
+}
+
+static void fill_page_cache_func(struct work_struct *work)
+{
+ struct kvfree_rcu_bulk_data *bnode;
+ struct kfree_rcu_cpu *krcp =
+ container_of(work, struct kfree_rcu_cpu,
+ page_cache_work.work);
+ unsigned long flags;
+ int nr_pages;
+ bool pushed;
+ int i;
+
+ nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
+ 1 : rcu_min_cached_objs;
+
+ for (i = READ_ONCE(krcp->nr_bkv_objs); i < nr_pages; i++) {
+ bnode = (struct kvfree_rcu_bulk_data *)
+ __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+
+ if (!bnode)
+ break;
+
+ raw_spin_lock_irqsave(&krcp->lock, flags);
+ pushed = put_cached_bnode(krcp, bnode);
+ raw_spin_unlock_irqrestore(&krcp->lock, flags);
+
+ if (!pushed) {
+ free_page((unsigned long) bnode);
+ break;
+ }
+ }
+
+ atomic_set(&krcp->work_in_progress, 0);
+ atomic_set(&krcp->backoff_page_cache_fill, 0);
+}
+
+static void
+run_page_cache_worker(struct kfree_rcu_cpu *krcp)
+{
+ // If cache disabled, bail out.
+ if (!rcu_min_cached_objs)
+ return;
+
+ if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
+ !atomic_xchg(&krcp->work_in_progress, 1)) {
+ if (atomic_read(&krcp->backoff_page_cache_fill)) {
+ queue_delayed_work(system_wq,
+ &krcp->page_cache_work,
+ msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
+ } else {
+ hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ krcp->hrtimer.function = schedule_page_work_fn;
+ hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
+ }
+ }
+}
+
+// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
+// state specified by flags. If can_alloc is true, the caller must
+// be schedulable and not be holding any locks or mutexes that might be
+// acquired by the memory allocator or anything that it might invoke.
+// Returns true if ptr was successfully recorded, else the caller must
+// use a fallback.
+static inline bool
+add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
+ unsigned long *flags, void *ptr, bool can_alloc)
+{
+ struct kvfree_rcu_bulk_data *bnode;
+ int idx;
+
+ *krcp = krc_this_cpu_lock(flags);
+ if (unlikely(!(*krcp)->initialized))
+ return false;
+
+ idx = !!is_vmalloc_addr(ptr);
+ bnode = list_first_entry_or_null(&(*krcp)->bulk_head[idx],
+ struct kvfree_rcu_bulk_data, list);
+
+ /* Check if a new block is required. */
+ if (!bnode || bnode->nr_records == KVFREE_BULK_MAX_ENTR) {
+ bnode = get_cached_bnode(*krcp);
+ if (!bnode && can_alloc) {
+ krc_this_cpu_unlock(*krcp, *flags);
+
+ // __GFP_NORETRY - allows a light-weight direct reclaim
+ // what is OK from minimizing of fallback hitting point of
+ // view. Apart of that it forbids any OOM invoking what is
+ // also beneficial since we are about to release memory soon.
+ //
+ // __GFP_NOMEMALLOC - prevents from consuming of all the
+ // memory reserves. Please note we have a fallback path.
+ //
+ // __GFP_NOWARN - it is supposed that an allocation can
+ // be failed under low memory or high memory pressure
+ // scenarios.
+ bnode = (struct kvfree_rcu_bulk_data *)
+ __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+ raw_spin_lock_irqsave(&(*krcp)->lock, *flags);
+ }
+
+ if (!bnode)
+ return false;
+
+ // Initialize the new block and attach it.
+ bnode->nr_records = 0;
+ list_add(&bnode->list, &(*krcp)->bulk_head[idx]);
+ }
+
+ // Finally insert and update the GP for this page.
+ bnode->records[bnode->nr_records++] = ptr;
+ get_state_synchronize_rcu_full(&bnode->gp_snap);
+ atomic_inc(&(*krcp)->bulk_count[idx]);
+
+ return true;
+}
+
+/*
+ * Queue a request for lazy invocation of the appropriate free routine
+ * after a grace period. Please note that three paths are maintained,
+ * two for the common case using arrays of pointers and a third one that
+ * is used only when the main paths cannot be used, for example, due to
+ * memory pressure.
+ *
+ * Each kvfree_call_rcu() request is added to a batch. The batch will be drained
+ * every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
+ * be free'd in workqueue context. This allows us to: batch requests together to
+ * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
+ */
+void kvfree_call_rcu(struct rcu_head *head, void *ptr)
+{
+ unsigned long flags;
+ struct kfree_rcu_cpu *krcp;
+ bool success;
+
+ /*
+ * Please note there is a limitation for the head-less
+ * variant, that is why there is a clear rule for such
+ * objects: it can be used from might_sleep() context
+ * only. For other places please embed an rcu_head to
+ * your data.
+ */
+ if (!head)
+ might_sleep();
+
+ // Queue the object but don't yet schedule the batch.
+ if (debug_rcu_head_queue(ptr)) {
+ // Probable double kfree_rcu(), just leak.
+ WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
+ __func__, head);
+
+ // Mark as success and leave.
+ return;
+ }
+
+ kasan_record_aux_stack_noalloc(ptr);
+ success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
+ if (!success) {
+ run_page_cache_worker(krcp);
+
+ if (head == NULL)
+ // Inline if kvfree_rcu(one_arg) call.
+ goto unlock_return;
+
+ head->func = ptr;
+ head->next = krcp->head;
+ WRITE_ONCE(krcp->head, head);
+ atomic_inc(&krcp->head_count);
+
+ // Take a snapshot for this krcp.
+ krcp->head_gp_snap = get_state_synchronize_rcu();
+ success = true;
+ }
+
+ /*
+ * The kvfree_rcu() caller considers the pointer freed at this point
+ * and likely removes any references to it. Since the actual slab
+ * freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore
+ * this object (no scanning or false positives reporting).
+ */
+ kmemleak_ignore(ptr);
+
+ // Set timer to drain after KFREE_DRAIN_JIFFIES.
+ if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
+ schedule_delayed_monitor_work(krcp);
+
+unlock_return:
+ krc_this_cpu_unlock(krcp, flags);
+
+ /*
+ * Inline kvfree() after synchronize_rcu(). We can do
+ * it from might_sleep() context only, so the current
+ * CPU can pass the QS state.
+ */
+ if (!success) {
+ debug_rcu_head_unqueue((struct rcu_head *) ptr);
+ synchronize_rcu();
+ kvfree(ptr);
+ }
+}
+EXPORT_SYMBOL_GPL(kvfree_call_rcu);
+
+static unsigned long
+kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
+{
+ int cpu;
+ unsigned long count = 0;
+
+ /* Snapshot count of all CPUs */
+ for_each_possible_cpu(cpu) {
+ struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+ count += krc_count(krcp);
+ count += READ_ONCE(krcp->nr_bkv_objs);
+ atomic_set(&krcp->backoff_page_cache_fill, 1);
+ }
+
+ return count == 0 ? SHRINK_EMPTY : count;
+}
+
+static unsigned long
+kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
+{
+ int cpu, freed = 0;
+
+ for_each_possible_cpu(cpu) {
+ int count;
+ struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+ count = krc_count(krcp);
+ count += drain_page_cache(krcp);
+ kfree_rcu_monitor(&krcp->monitor_work.work);
+
+ sc->nr_to_scan -= count;
+ freed += count;
+
+ if (sc->nr_to_scan <= 0)
+ break;
+ }
+
+ return freed == 0 ? SHRINK_STOP : freed;
+}
+
+static struct shrinker kfree_rcu_shrinker = {
+ .count_objects = kfree_rcu_shrink_count,
+ .scan_objects = kfree_rcu_shrink_scan,
+ .batch = 0,
+ .seeks = DEFAULT_SEEKS,
+};
+
+void __init kfree_rcu_scheduler_running(void)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu) {
+ struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+ if (need_offload_krc(krcp))
+ schedule_delayed_monitor_work(krcp);
+ }
+}
+
+/*
+ * During early boot, any blocking grace-period wait automatically
+ * implies a grace period.
+ *
+ * Later on, this could in theory be the case for kernels built with
+ * CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this
+ * is not a common case. Furthermore, this optimization would cause
+ * the rcu_gp_oldstate structure to expand by 50%, so this potential
+ * grace-period optimization is ignored once the scheduler is running.
+ */
+static int rcu_blocking_is_gp(void)
+{
+ if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) {
+ might_sleep();
+ return false;
+ }
+ return true;
+}
+
+/**
+ * synchronize_rcu - wait until a grace period has elapsed.
+ *
+ * Control will return to the caller some time after a full grace
+ * period has elapsed, in other words after all currently executing RCU
+ * read-side critical sections have completed. Note, however, that
+ * upon return from synchronize_rcu(), the caller might well be executing
+ * concurrently with new RCU read-side critical sections that began while
+ * synchronize_rcu() was waiting.
+ *
+ * RCU read-side critical sections are delimited by rcu_read_lock()
+ * and rcu_read_unlock(), and may be nested. In addition, but only in
+ * v5.0 and later, regions of code across which interrupts, preemption,
+ * or softirqs have been disabled also serve as RCU read-side critical
+ * sections. This includes hardware interrupt handlers, softirq handlers,
+ * and NMI handlers.
+ *
+ * Note that this guarantee implies further memory-ordering guarantees.
+ * On systems with more than one CPU, when synchronize_rcu() returns,
+ * each CPU is guaranteed to have executed a full memory barrier since
+ * the end of its last RCU read-side critical section whose beginning
+ * preceded the call to synchronize_rcu(). In addition, each CPU having
+ * an RCU read-side critical section that extends beyond the return from
+ * synchronize_rcu() is guaranteed to have executed a full memory barrier
+ * after the beginning of synchronize_rcu() and before the beginning of
+ * that RCU read-side critical section. Note that these guarantees include
+ * CPUs that are offline, idle, or executing in user mode, as well as CPUs
+ * that are executing in the kernel.
+ *
+ * Furthermore, if CPU A invoked synchronize_rcu(), which returned
+ * to its caller on CPU B, then both CPU A and CPU B are guaranteed
+ * to have executed a full memory barrier during the execution of
+ * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
+ * again only if the system has more than one CPU).
+ *
+ * Implementation of these memory-ordering guarantees is described here:
+ * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
+ */
+void synchronize_rcu(void)
+{
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+ lock_is_held(&rcu_lock_map) ||
+ lock_is_held(&rcu_sched_lock_map),
+ "Illegal synchronize_rcu() in RCU read-side critical section");
+ if (!rcu_blocking_is_gp()) {
+ if (rcu_gp_is_expedited())
+ synchronize_rcu_expedited();
+ else
+ wait_rcu_gp(call_rcu_hurry);
+ return;
+ }
+
+ // Context allows vacuous grace periods.
+ // Note well that this code runs with !PREEMPT && !SMP.
+ // In addition, all code that advances grace periods runs at
+ // process level. Therefore, this normal GP overlaps with other
+ // normal GPs only by being fully nested within them, which allows
+ // reuse of ->gp_seq_polled_snap.
+ rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
+ rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
+
+ // Update the normal grace-period counters to record
+ // this grace period, but only those used by the boot CPU.
+ // The rcu_scheduler_starting() will take care of the rest of
+ // these counters.
+ local_irq_save(flags);
+ WARN_ON_ONCE(num_online_cpus() > 1);
+ rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
+ for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent)
+ rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
+ local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+/**
+ * get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie
+ * @rgosp: Place to put state cookie
+ *
+ * Stores into @rgosp a value that will always be treated by functions
+ * like poll_state_synchronize_rcu_full() as a cookie whose grace period
+ * has already completed.
+ */
+void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
+ rgosp->rgos_exp = RCU_GET_STATE_COMPLETED;
+}
+EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
+
+/**
+ * get_state_synchronize_rcu - Snapshot current RCU state
+ *
+ * Returns a cookie that is used by a later call to cond_synchronize_rcu()
+ * or poll_state_synchronize_rcu() to determine whether or not a full
+ * grace period has elapsed in the meantime.
+ */
+unsigned long get_state_synchronize_rcu(void)
+{
+ /*
+ * Any prior manipulation of RCU-protected data must happen
+ * before the load from ->gp_seq.
+ */
+ smp_mb(); /* ^^^ */
+ return rcu_seq_snap(&rcu_state.gp_seq_polled);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
+
+/**
+ * get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited
+ * @rgosp: location to place combined normal/expedited grace-period state
+ *
+ * Places the normal and expedited grace-period states in @rgosp. This
+ * state value can be passed to a later call to cond_synchronize_rcu_full()
+ * or poll_state_synchronize_rcu_full() to determine whether or not a
+ * grace period (whether normal or expedited) has elapsed in the meantime.
+ * The rcu_gp_oldstate structure takes up twice the memory of an unsigned
+ * long, but is guaranteed to see all grace periods. In contrast, the
+ * combined state occupies less memory, but can sometimes fail to take
+ * grace periods into account.
+ *
+ * This does not guarantee that the needed grace period will actually
+ * start.
+ */
+void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ struct rcu_node *rnp = rcu_get_root();
+
+ /*
+ * Any prior manipulation of RCU-protected data must happen
+ * before the loads from ->gp_seq and ->expedited_sequence.
+ */
+ smp_mb(); /* ^^^ */
+ rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
+ rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
+}
+EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);
+
+/*
+ * Helper function for start_poll_synchronize_rcu() and
+ * start_poll_synchronize_rcu_full().
+ */
+static void start_poll_synchronize_rcu_common(void)
+{
+ unsigned long flags;
+ bool needwake;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ lockdep_assert_irqs_enabled();
+ local_irq_save(flags);
+ rdp = this_cpu_ptr(&rcu_data);
+ rnp = rdp->mynode;
+ raw_spin_lock_rcu_node(rnp); // irqs already disabled.
+ // Note it is possible for a grace period to have elapsed between
+ // the above call to get_state_synchronize_rcu() and the below call
+ // to rcu_seq_snap. This is OK, the worst that happens is that we
+ // get a grace period that no one needed. These accesses are ordered
+ // by smp_mb(), and we are accessing them in the opposite order
+ // from which they are updated at grace-period start, as required.
+ needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq));
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ if (needwake)
+ rcu_gp_kthread_wake();
+}
+
+/**
+ * start_poll_synchronize_rcu - Snapshot and start RCU grace period
+ *
+ * Returns a cookie that is used by a later call to cond_synchronize_rcu()
+ * or poll_state_synchronize_rcu() to determine whether or not a full
+ * grace period has elapsed in the meantime. If the needed grace period
+ * is not already slated to start, notifies RCU core of the need for that
+ * grace period.
+ *
+ * Interrupts must be enabled for the case where it is necessary to awaken
+ * the grace-period kthread.
+ */
+unsigned long start_poll_synchronize_rcu(void)
+{
+ unsigned long gp_seq = get_state_synchronize_rcu();
+
+ start_poll_synchronize_rcu_common();
+ return gp_seq;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
+
+/**
+ * start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period
+ * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
+ *
+ * Places the normal and expedited grace-period states in *@rgos. This
+ * state value can be passed to a later call to cond_synchronize_rcu_full()
+ * or poll_state_synchronize_rcu_full() to determine whether or not a
+ * grace period (whether normal or expedited) has elapsed in the meantime.
+ * If the needed grace period is not already slated to start, notifies
+ * RCU core of the need for that grace period.
+ *
+ * Interrupts must be enabled for the case where it is necessary to awaken
+ * the grace-period kthread.
+ */
+void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ get_state_synchronize_rcu_full(rgosp);
+
+ start_poll_synchronize_rcu_common();
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full);
+
+/**
+ * poll_state_synchronize_rcu - Has the specified RCU grace period completed?
+ * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
+ *
+ * If a full RCU grace period has elapsed since the earlier call from
+ * which @oldstate was obtained, return @true, otherwise return @false.
+ * If @false is returned, it is the caller's responsibility to invoke this
+ * function later on until it does return @true. Alternatively, the caller
+ * can explicitly wait for a grace period, for example, by passing @oldstate
+ * to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited()
+ * on the one hand or by directly invoking either synchronize_rcu() or
+ * synchronize_rcu_expedited() on the other.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited for
+ * more than a billion grace periods (and way more on a 64-bit system!).
+ * Those needing to keep old state values for very long time periods
+ * (many hours even on 32-bit systems) should check them occasionally and
+ * either refresh them or set a flag indicating that the grace period has
+ * completed. Alternatively, they can use get_completed_synchronize_rcu()
+ * to get a guaranteed-completed grace-period state.
+ *
+ * In addition, because oldstate compresses the grace-period state for
+ * both normal and expedited grace periods into a single unsigned long,
+ * it can miss a grace period when synchronize_rcu() runs concurrently
+ * with synchronize_rcu_expedited(). If this is unacceptable, please
+ * instead use the _full() variant of these polling APIs.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @oldstate, and that returned at the end
+ * of this function.
+ */
+bool poll_state_synchronize_rcu(unsigned long oldstate)
+{
+ if (oldstate == RCU_GET_STATE_COMPLETED ||
+ rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) {
+ smp_mb(); /* Ensure GP ends before subsequent accesses. */
+ return true;
+ }
+ return false;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
+
+/**
+ * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed?
+ * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
+ *
+ * If a full RCU grace period has elapsed since the earlier call from
+ * which *rgosp was obtained, return @true, otherwise return @false.
+ * If @false is returned, it is the caller's responsibility to invoke this
+ * function later on until it does return @true. Alternatively, the caller
+ * can explicitly wait for a grace period, for example, by passing @rgosp
+ * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited
+ * for more than a billion grace periods (and way more on a 64-bit
+ * system!). Those needing to keep rcu_gp_oldstate values for very
+ * long time periods (many hours even on 32-bit systems) should check
+ * them occasionally and either refresh them or set a flag indicating
+ * that the grace period has completed. Alternatively, they can use
+ * get_completed_synchronize_rcu_full() to get a guaranteed-completed
+ * grace-period state.
+ *
+ * This function provides the same memory-ordering guarantees that would
+ * be provided by a synchronize_rcu() that was invoked at the call to
+ * the function that provided @rgosp, and that returned at the end of this
+ * function. And this guarantee requires that the root rcu_node structure's
+ * ->gp_seq field be checked instead of that of the rcu_state structure.
+ * The problem is that the just-ending grace-period's callbacks can be
+ * invoked between the time that the root rcu_node structure's ->gp_seq
+ * field is updated and the time that the rcu_state structure's ->gp_seq
+ * field is updated. Therefore, if a single synchronize_rcu() is to
+ * cause a subsequent poll_state_synchronize_rcu_full() to return @true,
+ * then the root rcu_node structure is the one that needs to be polled.
+ */
+bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ struct rcu_node *rnp = rcu_get_root();
+
+ smp_mb(); // Order against root rcu_node structure grace-period cleanup.
+ if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED ||
+ rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) ||
+ rgosp->rgos_exp == RCU_GET_STATE_COMPLETED ||
+ rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) {
+ smp_mb(); /* Ensure GP ends before subsequent accesses. */
+ return true;
+ }
+ return false;
+}
+EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
+
+/**
+ * cond_synchronize_rcu - Conditionally wait for an RCU grace period
+ * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
+ *
+ * If a full RCU grace period has elapsed since the earlier call to
+ * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
+ * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for a couple of additional grace periods should be just fine.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @oldstate and that returned at the end
+ * of this function.
+ */
+void cond_synchronize_rcu(unsigned long oldstate)
+{
+ if (!poll_state_synchronize_rcu(oldstate))
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
+
+/**
+ * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period
+ * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
+ *
+ * If a full RCU grace period has elapsed since the call to
+ * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
+ * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
+ * obtained, just return. Otherwise, invoke synchronize_rcu() to wait
+ * for a full grace period.
+ *
+ * Yes, this function does not take counter wrap into account.
+ * But counter wrap is harmless. If the counter wraps, we have waited for
+ * more than 2 billion grace periods (and way more on a 64-bit system!),
+ * so waiting for a couple of additional grace periods should be just fine.
+ *
+ * This function provides the same memory-ordering guarantees that
+ * would be provided by a synchronize_rcu() that was invoked at the call
+ * to the function that provided @rgosp and that returned at the end of
+ * this function.
+ */
+void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
+{
+ if (!poll_state_synchronize_rcu_full(rgosp))
+ synchronize_rcu();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
+
+/*
+ * Check to see if there is any immediate RCU-related work to be done by
+ * the current CPU, returning 1 if so and zero otherwise. The checks are
+ * in order of increasing expense: checks that can be carried out against
+ * CPU-local state are performed first. However, we must check for CPU
+ * stalls first, else we might not get a chance.
+ */
+static int rcu_pending(int user)
+{
+ bool gp_in_progress;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ struct rcu_node *rnp = rdp->mynode;
+
+ lockdep_assert_irqs_disabled();
+
+ /* Check for CPU stalls, if enabled. */
+ check_cpu_stall(rdp);
+
+ /* Does this CPU need a deferred NOCB wakeup? */
+ if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
+ return 1;
+
+ /* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
+ if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
+ return 0;
+
+ /* Is the RCU core waiting for a quiescent state from this CPU? */
+ gp_in_progress = rcu_gp_in_progress();
+ if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
+ return 1;
+
+ /* Does this CPU have callbacks ready to invoke? */
+ if (!rcu_rdp_is_offloaded(rdp) &&
+ rcu_segcblist_ready_cbs(&rdp->cblist))
+ return 1;
+
+ /* Has RCU gone idle with this CPU needing another grace period? */
+ if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
+ !rcu_rdp_is_offloaded(rdp) &&
+ !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
+ return 1;
+
+ /* Have RCU grace period completed or started? */
+ if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
+ unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
+ return 1;
+
+ /* nothing to do */
+ return 0;
+}
+
+/*
+ * Helper function for rcu_barrier() tracing. If tracing is disabled,
+ * the compiler is expected to optimize this away.
+ */
+static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
+{
+ trace_rcu_barrier(rcu_state.name, s, cpu,
+ atomic_read(&rcu_state.barrier_cpu_count), done);
+}
+
+/*
+ * RCU callback function for rcu_barrier(). If we are last, wake
+ * up the task executing rcu_barrier().
+ *
+ * Note that the value of rcu_state.barrier_sequence must be captured
+ * before the atomic_dec_and_test(). Otherwise, if this CPU is not last,
+ * other CPUs might count the value down to zero before this CPU gets
+ * around to invoking rcu_barrier_trace(), which might result in bogus
+ * data from the next instance of rcu_barrier().
+ */
+static void rcu_barrier_callback(struct rcu_head *rhp)
+{
+ unsigned long __maybe_unused s = rcu_state.barrier_sequence;
+
+ if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
+ rcu_barrier_trace(TPS("LastCB"), -1, s);
+ complete(&rcu_state.barrier_completion);
+ } else {
+ rcu_barrier_trace(TPS("CB"), -1, s);
+ }
+}
+
+/*
+ * If needed, entrain an rcu_barrier() callback on rdp->cblist.
+ */
+static void rcu_barrier_entrain(struct rcu_data *rdp)
+{
+ unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence);
+ unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap);
+ bool wake_nocb = false;
+ bool was_alldone = false;
+
+ lockdep_assert_held(&rcu_state.barrier_lock);
+ if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq))
+ return;
+ rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
+ rdp->barrier_head.func = rcu_barrier_callback;
+ debug_rcu_head_queue(&rdp->barrier_head);
+ rcu_nocb_lock(rdp);
+ /*
+ * Flush bypass and wakeup rcuog if we add callbacks to an empty regular
+ * queue. This way we don't wait for bypass timer that can reach seconds
+ * if it's fully lazy.
+ */
+ was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist);
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
+ wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist);
+ if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
+ atomic_inc(&rcu_state.barrier_cpu_count);
+ } else {
+ debug_rcu_head_unqueue(&rdp->barrier_head);
+ rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence);
+ }
+ rcu_nocb_unlock(rdp);
+ if (wake_nocb)
+ wake_nocb_gp(rdp, false);
+ smp_store_release(&rdp->barrier_seq_snap, gseq);
+}
+
+/*
+ * Called with preemption disabled, and from cross-cpu IRQ context.
+ */
+static void rcu_barrier_handler(void *cpu_in)
+{
+ uintptr_t cpu = (uintptr_t)cpu_in;
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ lockdep_assert_irqs_disabled();
+ WARN_ON_ONCE(cpu != rdp->cpu);
+ WARN_ON_ONCE(cpu != smp_processor_id());
+ raw_spin_lock(&rcu_state.barrier_lock);
+ rcu_barrier_entrain(rdp);
+ raw_spin_unlock(&rcu_state.barrier_lock);
+}
+
+/**
+ * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
+ *
+ * Note that this primitive does not necessarily wait for an RCU grace period
+ * to complete. For example, if there are no RCU callbacks queued anywhere
+ * in the system, then rcu_barrier() is within its rights to return
+ * immediately, without waiting for anything, much less an RCU grace period.
+ */
+void rcu_barrier(void)
+{
+ uintptr_t cpu;
+ unsigned long flags;
+ unsigned long gseq;
+ struct rcu_data *rdp;
+ unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
+
+ rcu_barrier_trace(TPS("Begin"), -1, s);
+
+ /* Take mutex to serialize concurrent rcu_barrier() requests. */
+ mutex_lock(&rcu_state.barrier_mutex);
+
+ /* Did someone else do our work for us? */
+ if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
+ rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
+ smp_mb(); /* caller's subsequent code after above check. */
+ mutex_unlock(&rcu_state.barrier_mutex);
+ return;
+ }
+
+ /* Mark the start of the barrier operation. */
+ raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
+ rcu_seq_start(&rcu_state.barrier_sequence);
+ gseq = rcu_state.barrier_sequence;
+ rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
+
+ /*
+ * Initialize the count to two rather than to zero in order
+ * to avoid a too-soon return to zero in case of an immediate
+ * invocation of the just-enqueued callback (or preemption of
+ * this task). Exclude CPU-hotplug operations to ensure that no
+ * offline non-offloaded CPU has callbacks queued.
+ */
+ init_completion(&rcu_state.barrier_completion);
+ atomic_set(&rcu_state.barrier_cpu_count, 2);
+ raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
+
+ /*
+ * Force each CPU with callbacks to register a new callback.
+ * When that callback is invoked, we will know that all of the
+ * corresponding CPU's preceding callbacks have been invoked.
+ */
+ for_each_possible_cpu(cpu) {
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+retry:
+ if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq)
+ continue;
+ raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
+ if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
+ WRITE_ONCE(rdp->barrier_seq_snap, gseq);
+ raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
+ rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
+ continue;
+ }
+ if (!rcu_rdp_cpu_online(rdp)) {
+ rcu_barrier_entrain(rdp);
+ WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
+ raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
+ rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
+ continue;
+ }
+ raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
+ if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
+ schedule_timeout_uninterruptible(1);
+ goto retry;
+ }
+ WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
+ rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
+ }
+
+ /*
+ * Now that we have an rcu_barrier_callback() callback on each
+ * CPU, and thus each counted, remove the initial count.
+ */
+ if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
+ complete(&rcu_state.barrier_completion);
+
+ /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
+ wait_for_completion(&rcu_state.barrier_completion);
+
+ /* Mark the end of the barrier operation. */
+ rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
+ rcu_seq_end(&rcu_state.barrier_sequence);
+ gseq = rcu_state.barrier_sequence;
+ for_each_possible_cpu(cpu) {
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ WRITE_ONCE(rdp->barrier_seq_snap, gseq);
+ }
+
+ /* Other rcu_barrier() invocations can now safely proceed. */
+ mutex_unlock(&rcu_state.barrier_mutex);
+}
+EXPORT_SYMBOL_GPL(rcu_barrier);
+
+/*
+ * Compute the mask of online CPUs for the specified rcu_node structure.
+ * This will not be stable unless the rcu_node structure's ->lock is
+ * held, but the bit corresponding to the current CPU will be stable
+ * in most contexts.
+ */
+static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
+{
+ return READ_ONCE(rnp->qsmaskinitnext);
+}
+
+/*
+ * Is the CPU corresponding to the specified rcu_data structure online
+ * from RCU's perspective? This perspective is given by that structure's
+ * ->qsmaskinitnext field rather than by the global cpu_online_mask.
+ */
+static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
+{
+ return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
+}
+
+bool rcu_cpu_online(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ return rcu_rdp_cpu_online(rdp);
+}
+
+#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
+
+/*
+ * Is the current CPU online as far as RCU is concerned?
+ *
+ * Disable preemption to avoid false positives that could otherwise
+ * happen due to the current CPU number being sampled, this task being
+ * preempted, its old CPU being taken offline, resuming on some other CPU,
+ * then determining that its old CPU is now offline.
+ *
+ * Disable checking if in an NMI handler because we cannot safely
+ * report errors from NMI handlers anyway. In addition, it is OK to use
+ * RCU on an offline processor during initial boot, hence the check for
+ * rcu_scheduler_fully_active.
+ */
+bool rcu_lockdep_current_cpu_online(void)
+{
+ struct rcu_data *rdp;
+ bool ret = false;
+
+ if (in_nmi() || !rcu_scheduler_fully_active)
+ return true;
+ preempt_disable_notrace();
+ rdp = this_cpu_ptr(&rcu_data);
+ /*
+ * Strictly, we care here about the case where the current CPU is
+ * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
+ * not being up to date. So arch_spin_is_locked() might have a
+ * false positive if it's held by some *other* CPU, but that's
+ * OK because that just means a false *negative* on the warning.
+ */
+ if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
+ ret = true;
+ preempt_enable_notrace();
+ return ret;
+}
+EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
+
+#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
+
+// Has rcu_init() been invoked? This is used (for example) to determine
+// whether spinlocks may be acquired safely.
+static bool rcu_init_invoked(void)
+{
+ return !!rcu_state.n_online_cpus;
+}
+
+/*
+ * Near the end of the offline process. Trace the fact that this CPU
+ * is going offline.
+ */
+int rcutree_dying_cpu(unsigned int cpu)
+{
+ bool blkd;
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct rcu_node *rnp = rdp->mynode;
+
+ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ return 0;
+
+ blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
+ trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
+ blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
+ return 0;
+}
+
+/*
+ * All CPUs for the specified rcu_node structure have gone offline,
+ * and all tasks that were preempted within an RCU read-side critical
+ * section while running on one of those CPUs have since exited their RCU
+ * read-side critical section. Some other CPU is reporting this fact with
+ * the specified rcu_node structure's ->lock held and interrupts disabled.
+ * This function therefore goes up the tree of rcu_node structures,
+ * clearing the corresponding bits in the ->qsmaskinit fields. Note that
+ * the leaf rcu_node structure's ->qsmaskinit field has already been
+ * updated.
+ *
+ * This function does check that the specified rcu_node structure has
+ * all CPUs offline and no blocked tasks, so it is OK to invoke it
+ * prematurely. That said, invoking it after the fact will cost you
+ * a needless lock acquisition. So once it has done its work, don't
+ * invoke it again.
+ */
+static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
+{
+ long mask;
+ struct rcu_node *rnp = rnp_leaf;
+
+ raw_lockdep_assert_held_rcu_node(rnp_leaf);
+ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
+ WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
+ WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
+ return;
+ for (;;) {
+ mask = rnp->grpmask;
+ rnp = rnp->parent;
+ if (!rnp)
+ break;
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+ rnp->qsmaskinit &= ~mask;
+ /* Between grace periods, so better already be zero! */
+ WARN_ON_ONCE(rnp->qsmask);
+ if (rnp->qsmaskinit) {
+ raw_spin_unlock_rcu_node(rnp);
+ /* irqs remain disabled. */
+ return;
+ }
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+ }
+}
+
+/*
+ * The CPU has been completely removed, and some other CPU is reporting
+ * this fact from process context. Do the remainder of the cleanup.
+ * There can only be one CPU hotplug operation at a time, so no need for
+ * explicit locking.
+ */
+int rcutree_dead_cpu(unsigned int cpu)
+{
+ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
+ return 0;
+
+ WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
+ // Stop-machine done, so allow nohz_full to disable tick.
+ tick_dep_clear(TICK_DEP_BIT_RCU);
+ return 0;
+}
+
+/*
+ * Propagate ->qsinitmask bits up the rcu_node tree to account for the
+ * first CPU in a given leaf rcu_node structure coming online. The caller
+ * must hold the corresponding leaf rcu_node ->lock with interrupts
+ * disabled.
+ */
+static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
+{
+ long mask;
+ long oldmask;
+ struct rcu_node *rnp = rnp_leaf;
+
+ raw_lockdep_assert_held_rcu_node(rnp_leaf);
+ WARN_ON_ONCE(rnp->wait_blkd_tasks);
+ for (;;) {
+ mask = rnp->grpmask;
+ rnp = rnp->parent;
+ if (rnp == NULL)
+ return;
+ raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
+ oldmask = rnp->qsmaskinit;
+ rnp->qsmaskinit |= mask;
+ raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
+ if (oldmask)
+ return;
+ }
+}
+
+/*
+ * Do boot-time initialization of a CPU's per-CPU RCU data.
+ */
+static void __init
+rcu_boot_init_percpu_data(int cpu)
+{
+ struct context_tracking *ct = this_cpu_ptr(&context_tracking);
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ /* Set up local state, ensuring consistent view of global state. */
+ rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
+ INIT_WORK(&rdp->strict_work, strict_work_handler);
+ WARN_ON_ONCE(ct->dynticks_nesting != 1);
+ WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
+ rdp->barrier_seq_snap = rcu_state.barrier_sequence;
+ rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
+ rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
+ rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
+ rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
+ rdp->last_sched_clock = jiffies;
+ rdp->cpu = cpu;
+ rcu_boot_init_nocb_percpu_data(rdp);
+}
+
+/*
+ * Invoked early in the CPU-online process, when pretty much all services
+ * are available. The incoming CPU is not present.
+ *
+ * Initializes a CPU's per-CPU RCU data. Note that only one online or
+ * offline event can be happening at a given time. Note also that we can
+ * accept some slop in the rsp->gp_seq access due to the fact that this
+ * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
+ * And any offloaded callbacks are being numbered elsewhere.
+ */
+int rcutree_prepare_cpu(unsigned int cpu)
+{
+ unsigned long flags;
+ struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct rcu_node *rnp = rcu_get_root();
+
+ /* Set up local state, ensuring consistent view of global state. */
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rdp->qlen_last_fqs_check = 0;
+ rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
+ rdp->blimit = blimit;
+ ct->dynticks_nesting = 1; /* CPU not up, no tearing. */
+ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
+
+ /*
+ * Only non-NOCB CPUs that didn't have early-boot callbacks need to be
+ * (re-)initialized.
+ */
+ if (!rcu_segcblist_is_enabled(&rdp->cblist))
+ rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
+
+ /*
+ * Add CPU to leaf rcu_node pending-online bitmask. Any needed
+ * propagation up the rcu_node tree will happen at the beginning
+ * of the next grace period.
+ */
+ rnp = rdp->mynode;
+ raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+ rdp->gp_seq = READ_ONCE(rnp->gp_seq);
+ rdp->gp_seq_needed = rdp->gp_seq;
+ rdp->cpu_no_qs.b.norm = true;
+ rdp->core_needs_qs = false;
+ rdp->rcu_iw_pending = false;
+ rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
+ rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
+ trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ rcu_spawn_one_boost_kthread(rnp);
+ rcu_spawn_cpu_nocb_kthread(cpu);
+ WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
+
+ return 0;
+}
+
+/*
+ * Update RCU priority boot kthread affinity for CPU-hotplug changes.
+ */
+static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
+{
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
+}
+
+/*
+ * Has the specified (known valid) CPU ever been fully online?
+ */
+bool rcu_cpu_beenfullyonline(int cpu)
+{
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+
+ return smp_load_acquire(&rdp->beenonline);
+}
+
+/*
+ * Near the end of the CPU-online process. Pretty much all services
+ * enabled, and the CPU is now very much alive.
+ */
+int rcutree_online_cpu(unsigned int cpu)
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ rnp = rdp->mynode;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rnp->ffmask |= rdp->grpmask;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+ return 0; /* Too early in boot for scheduler work. */
+ sync_sched_exp_online_cleanup(cpu);
+ rcutree_affinity_setting(cpu, -1);
+
+ // Stop-machine done, so allow nohz_full to disable tick.
+ tick_dep_clear(TICK_DEP_BIT_RCU);
+ return 0;
+}
+
+/*
+ * Near the beginning of the process. The CPU is still very much alive
+ * with pretty much all services enabled.
+ */
+int rcutree_offline_cpu(unsigned int cpu)
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ rnp = rdp->mynode;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ rnp->ffmask &= ~rdp->grpmask;
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+ rcutree_affinity_setting(cpu, cpu);
+
+ // nohz_full CPUs need the tick for stop-machine to work quickly
+ tick_dep_set(TICK_DEP_BIT_RCU);
+ return 0;
+}
+
+/*
+ * Mark the specified CPU as being online so that subsequent grace periods
+ * (both expedited and normal) will wait on it. Note that this means that
+ * incoming CPUs are not allowed to use RCU read-side critical sections
+ * until this function is called. Failing to observe this restriction
+ * will result in lockdep splats.
+ *
+ * Note that this function is special in that it is invoked directly
+ * from the incoming CPU rather than from the cpuhp_step mechanism.
+ * This is because this function must be invoked at a precise location.
+ * This incoming CPU must not have enabled interrupts yet.
+ */
+void rcu_cpu_starting(unsigned int cpu)
+{
+ unsigned long mask;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ bool newcpu;
+
+ lockdep_assert_irqs_disabled();
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ if (rdp->cpu_started)
+ return;
+ rdp->cpu_started = true;
+
+ rnp = rdp->mynode;
+ mask = rdp->grpmask;
+ arch_spin_lock(&rcu_state.ofl_lock);
+ rcu_dynticks_eqs_online();
+ raw_spin_lock(&rcu_state.barrier_lock);
+ raw_spin_lock_rcu_node(rnp);
+ WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
+ raw_spin_unlock(&rcu_state.barrier_lock);
+ newcpu = !(rnp->expmaskinitnext & mask);
+ rnp->expmaskinitnext |= mask;
+ /* Allow lockless access for expedited grace periods. */
+ smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
+ ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
+ rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
+ rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
+ rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
+
+ /* An incoming CPU should never be blocking a grace period. */
+ if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
+ /* rcu_report_qs_rnp() *really* wants some flags to restore */
+ unsigned long flags;
+
+ local_irq_save(flags);
+ rcu_disable_urgency_upon_qs(rdp);
+ /* Report QS -after- changing ->qsmaskinitnext! */
+ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
+ } else {
+ raw_spin_unlock_rcu_node(rnp);
+ }
+ arch_spin_unlock(&rcu_state.ofl_lock);
+ smp_store_release(&rdp->beenonline, true);
+ smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
+}
+
+/*
+ * The outgoing function has no further need of RCU, so remove it from
+ * the rcu_node tree's ->qsmaskinitnext bit masks.
+ *
+ * Note that this function is special in that it is invoked directly
+ * from the outgoing CPU rather than from the cpuhp_step mechanism.
+ * This is because this function must be invoked at a precise location.
+ */
+void rcu_report_dead(unsigned int cpu)
+{
+ unsigned long flags, seq_flags;
+ unsigned long mask;
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
+
+ // Do any dangling deferred wakeups.
+ do_nocb_deferred_wakeup(rdp);
+
+ rcu_preempt_deferred_qs(current);
+
+ /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
+ mask = rdp->grpmask;
+ local_irq_save(seq_flags);
+ arch_spin_lock(&rcu_state.ofl_lock);
+ raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
+ rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
+ rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
+ if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
+ /* Report quiescent state -before- changing ->qsmaskinitnext! */
+ rcu_disable_urgency_upon_qs(rdp);
+ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ }
+ WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ arch_spin_unlock(&rcu_state.ofl_lock);
+ local_irq_restore(seq_flags);
+
+ rdp->cpu_started = false;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * The outgoing CPU has just passed through the dying-idle state, and we
+ * are being invoked from the CPU that was IPIed to continue the offline
+ * operation. Migrate the outgoing CPU's callbacks to the current CPU.
+ */
+void rcutree_migrate_callbacks(int cpu)
+{
+ unsigned long flags;
+ struct rcu_data *my_rdp;
+ struct rcu_node *my_rnp;
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ bool needwake;
+
+ if (rcu_rdp_is_offloaded(rdp) ||
+ rcu_segcblist_empty(&rdp->cblist))
+ return; /* No callbacks to migrate. */
+
+ raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
+ WARN_ON_ONCE(rcu_rdp_cpu_online(rdp));
+ rcu_barrier_entrain(rdp);
+ my_rdp = this_cpu_ptr(&rcu_data);
+ my_rnp = my_rdp->mynode;
+ rcu_nocb_lock(my_rdp); /* irqs already disabled. */
+ WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false));
+ raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
+ /* Leverage recent GPs and set GP for new callbacks. */
+ needwake = rcu_advance_cbs(my_rnp, rdp) ||
+ rcu_advance_cbs(my_rnp, my_rdp);
+ rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
+ raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */
+ needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
+ rcu_segcblist_disable(&rdp->cblist);
+ WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
+ check_cb_ovld_locked(my_rdp, my_rnp);
+ if (rcu_rdp_is_offloaded(my_rdp)) {
+ raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
+ __call_rcu_nocb_wake(my_rdp, true, flags);
+ } else {
+ rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
+ raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
+ }
+ if (needwake)
+ rcu_gp_kthread_wake();
+ lockdep_assert_irqs_enabled();
+ WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
+ !rcu_segcblist_empty(&rdp->cblist),
+ "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
+ cpu, rcu_segcblist_n_cbs(&rdp->cblist),
+ rcu_segcblist_first_cb(&rdp->cblist));
+}
+#endif
+
+/*
+ * On non-huge systems, use expedited RCU grace periods to make suspend
+ * and hibernation run faster.
+ */
+static int rcu_pm_notify(struct notifier_block *self,
+ unsigned long action, void *hcpu)
+{
+ switch (action) {
+ case PM_HIBERNATION_PREPARE:
+ case PM_SUSPEND_PREPARE:
+ rcu_async_hurry();
+ rcu_expedite_gp();
+ break;
+ case PM_POST_HIBERNATION:
+ case PM_POST_SUSPEND:
+ rcu_unexpedite_gp();
+ rcu_async_relax();
+ break;
+ default:
+ break;
+ }
+ return NOTIFY_OK;
+}
+
+#ifdef CONFIG_RCU_EXP_KTHREAD
+struct kthread_worker *rcu_exp_gp_kworker;
+struct kthread_worker *rcu_exp_par_gp_kworker;
+
+static void __init rcu_start_exp_gp_kworkers(void)
+{
+ const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
+ const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
+ struct sched_param param = { .sched_priority = kthread_prio };
+
+ rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
+ if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
+ pr_err("Failed to create %s!\n", gp_kworker_name);
+ return;
+ }
+
+ rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
+ if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
+ pr_err("Failed to create %s!\n", par_gp_kworker_name);
+ kthread_destroy_worker(rcu_exp_gp_kworker);
+ return;
+ }
+
+ sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, &param);
+ sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
+ &param);
+}
+
+static inline void rcu_alloc_par_gp_wq(void)
+{
+}
+#else /* !CONFIG_RCU_EXP_KTHREAD */
+struct workqueue_struct *rcu_par_gp_wq;
+
+static void __init rcu_start_exp_gp_kworkers(void)
+{
+}
+
+static inline void rcu_alloc_par_gp_wq(void)
+{
+ rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
+ WARN_ON(!rcu_par_gp_wq);
+}
+#endif /* CONFIG_RCU_EXP_KTHREAD */
+
+/*
+ * Spawn the kthreads that handle RCU's grace periods.
+ */
+static int __init rcu_spawn_gp_kthread(void)
+{
+ unsigned long flags;
+ struct rcu_node *rnp;
+ struct sched_param sp;
+ struct task_struct *t;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+ rcu_scheduler_fully_active = 1;
+ t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
+ if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
+ return 0;
+ if (kthread_prio) {
+ sp.sched_priority = kthread_prio;
+ sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+ }
+ rnp = rcu_get_root();
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ WRITE_ONCE(rcu_state.gp_activity, jiffies);
+ WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
+ // Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
+ smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ wake_up_process(t);
+ /* This is a pre-SMP initcall, we expect a single CPU */
+ WARN_ON(num_online_cpus() > 1);
+ /*
+ * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
+ * due to rcu_scheduler_fully_active.
+ */
+ rcu_spawn_cpu_nocb_kthread(smp_processor_id());
+ rcu_spawn_one_boost_kthread(rdp->mynode);
+ rcu_spawn_core_kthreads();
+ /* Create kthread worker for expedited GPs */
+ rcu_start_exp_gp_kworkers();
+ return 0;
+}
+early_initcall(rcu_spawn_gp_kthread);
+
+/*
+ * This function is invoked towards the end of the scheduler's
+ * initialization process. Before this is called, the idle task might
+ * contain synchronous grace-period primitives (during which time, this idle
+ * task is booting the system, and such primitives are no-ops). After this
+ * function is called, any synchronous grace-period primitives are run as
+ * expedited, with the requesting task driving the grace period forward.
+ * A later core_initcall() rcu_set_runtime_mode() will switch to full
+ * runtime RCU functionality.
+ */
+void rcu_scheduler_starting(void)
+{
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ WARN_ON(num_online_cpus() != 1);
+ WARN_ON(nr_context_switches() > 0);
+ rcu_test_sync_prims();
+
+ // Fix up the ->gp_seq counters.
+ local_irq_save(flags);
+ rcu_for_each_node_breadth_first(rnp)
+ rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
+ local_irq_restore(flags);
+
+ // Switch out of early boot mode.
+ rcu_scheduler_active = RCU_SCHEDULER_INIT;
+ rcu_test_sync_prims();
+}
+
+/*
+ * Helper function for rcu_init() that initializes the rcu_state structure.
+ */
+static void __init rcu_init_one(void)
+{
+ static const char * const buf[] = RCU_NODE_NAME_INIT;
+ static const char * const fqs[] = RCU_FQS_NAME_INIT;
+ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
+ static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
+
+ int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
+ int cpustride = 1;
+ int i;
+ int j;
+ struct rcu_node *rnp;
+
+ BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
+
+ /* Silence gcc 4.8 false positive about array index out of range. */
+ if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
+ panic("rcu_init_one: rcu_num_lvls out of range");
+
+ /* Initialize the level-tracking arrays. */
+
+ for (i = 1; i < rcu_num_lvls; i++)
+ rcu_state.level[i] =
+ rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
+ rcu_init_levelspread(levelspread, num_rcu_lvl);
+
+ /* Initialize the elements themselves, starting from the leaves. */
+
+ for (i = rcu_num_lvls - 1; i >= 0; i--) {
+ cpustride *= levelspread[i];
+ rnp = rcu_state.level[i];
+ for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
+ raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
+ lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
+ &rcu_node_class[i], buf[i]);
+ raw_spin_lock_init(&rnp->fqslock);
+ lockdep_set_class_and_name(&rnp->fqslock,
+ &rcu_fqs_class[i], fqs[i]);
+ rnp->gp_seq = rcu_state.gp_seq;
+ rnp->gp_seq_needed = rcu_state.gp_seq;
+ rnp->completedqs = rcu_state.gp_seq;
+ rnp->qsmask = 0;
+ rnp->qsmaskinit = 0;
+ rnp->grplo = j * cpustride;
+ rnp->grphi = (j + 1) * cpustride - 1;
+ if (rnp->grphi >= nr_cpu_ids)
+ rnp->grphi = nr_cpu_ids - 1;
+ if (i == 0) {
+ rnp->grpnum = 0;
+ rnp->grpmask = 0;
+ rnp->parent = NULL;
+ } else {
+ rnp->grpnum = j % levelspread[i - 1];
+ rnp->grpmask = BIT(rnp->grpnum);
+ rnp->parent = rcu_state.level[i - 1] +
+ j / levelspread[i - 1];
+ }
+ rnp->level = i;
+ INIT_LIST_HEAD(&rnp->blkd_tasks);
+ rcu_init_one_nocb(rnp);
+ init_waitqueue_head(&rnp->exp_wq[0]);
+ init_waitqueue_head(&rnp->exp_wq[1]);
+ init_waitqueue_head(&rnp->exp_wq[2]);
+ init_waitqueue_head(&rnp->exp_wq[3]);
+ spin_lock_init(&rnp->exp_lock);
+ mutex_init(&rnp->boost_kthread_mutex);
+ raw_spin_lock_init(&rnp->exp_poll_lock);
+ rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+ INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
+ }
+ }
+
+ init_swait_queue_head(&rcu_state.gp_wq);
+ init_swait_queue_head(&rcu_state.expedited_wq);
+ rnp = rcu_first_leaf_node();
+ for_each_possible_cpu(i) {
+ while (i > rnp->grphi)
+ rnp++;
+ per_cpu_ptr(&rcu_data, i)->mynode = rnp;
+ rcu_boot_init_percpu_data(i);
+ }
+}
+
+/*
+ * Force priority from the kernel command-line into range.
+ */
+static void __init sanitize_kthread_prio(void)
+{
+ int kthread_prio_in = kthread_prio;
+
+ if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
+ && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
+ kthread_prio = 2;
+ else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
+ kthread_prio = 1;
+ else if (kthread_prio < 0)
+ kthread_prio = 0;
+ else if (kthread_prio > 99)
+ kthread_prio = 99;
+
+ if (kthread_prio != kthread_prio_in)
+ pr_alert("%s: Limited prio to %d from %d\n",
+ __func__, kthread_prio, kthread_prio_in);
+}
+
+/*
+ * Compute the rcu_node tree geometry from kernel parameters. This cannot
+ * replace the definitions in tree.h because those are needed to size
+ * the ->node array in the rcu_state structure.
+ */
+void rcu_init_geometry(void)
+{
+ ulong d;
+ int i;
+ static unsigned long old_nr_cpu_ids;
+ int rcu_capacity[RCU_NUM_LVLS];
+ static bool initialized;
+
+ if (initialized) {
+ /*
+ * Warn if setup_nr_cpu_ids() had not yet been invoked,
+ * unless nr_cpus_ids == NR_CPUS, in which case who cares?
+ */
+ WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
+ return;
+ }
+
+ old_nr_cpu_ids = nr_cpu_ids;
+ initialized = true;
+
+ /*
+ * Initialize any unspecified boot parameters.
+ * The default values of jiffies_till_first_fqs and
+ * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
+ * value, which is a function of HZ, then adding one for each
+ * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
+ */
+ d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
+ if (jiffies_till_first_fqs == ULONG_MAX)
+ jiffies_till_first_fqs = d;
+ if (jiffies_till_next_fqs == ULONG_MAX)
+ jiffies_till_next_fqs = d;
+ adjust_jiffies_till_sched_qs();
+
+ /* If the compile-time values are accurate, just leave. */
+ if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
+ nr_cpu_ids == NR_CPUS)
+ return;
+ pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
+ rcu_fanout_leaf, nr_cpu_ids);
+
+ /*
+ * The boot-time rcu_fanout_leaf parameter must be at least two
+ * and cannot exceed the number of bits in the rcu_node masks.
+ * Complain and fall back to the compile-time values if this
+ * limit is exceeded.
+ */
+ if (rcu_fanout_leaf < 2 ||
+ rcu_fanout_leaf > sizeof(unsigned long) * 8) {
+ rcu_fanout_leaf = RCU_FANOUT_LEAF;
+ WARN_ON(1);
+ return;
+ }
+
+ /*
+ * Compute number of nodes that can be handled an rcu_node tree
+ * with the given number of levels.
+ */
+ rcu_capacity[0] = rcu_fanout_leaf;
+ for (i = 1; i < RCU_NUM_LVLS; i++)
+ rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
+
+ /*
+ * The tree must be able to accommodate the configured number of CPUs.
+ * If this limit is exceeded, fall back to the compile-time values.
+ */
+ if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
+ rcu_fanout_leaf = RCU_FANOUT_LEAF;
+ WARN_ON(1);
+ return;
+ }
+
+ /* Calculate the number of levels in the tree. */
+ for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
+ }
+ rcu_num_lvls = i + 1;
+
+ /* Calculate the number of rcu_nodes at each level of the tree. */
+ for (i = 0; i < rcu_num_lvls; i++) {
+ int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
+ num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
+ }
+
+ /* Calculate the total number of rcu_node structures. */
+ rcu_num_nodes = 0;
+ for (i = 0; i < rcu_num_lvls; i++)
+ rcu_num_nodes += num_rcu_lvl[i];
+}
+
+/*
+ * Dump out the structure of the rcu_node combining tree associated
+ * with the rcu_state structure.
+ */
+static void __init rcu_dump_rcu_node_tree(void)
+{
+ int level = 0;
+ struct rcu_node *rnp;
+
+ pr_info("rcu_node tree layout dump\n");
+ pr_info(" ");
+ rcu_for_each_node_breadth_first(rnp) {
+ if (rnp->level != level) {
+ pr_cont("\n");
+ pr_info(" ");
+ level = rnp->level;
+ }
+ pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
+ }
+ pr_cont("\n");
+}
+
+struct workqueue_struct *rcu_gp_wq;
+
+static void __init kfree_rcu_batch_init(void)
+{
+ int cpu;
+ int i, j;
+
+ /* Clamp it to [0:100] seconds interval. */
+ if (rcu_delay_page_cache_fill_msec < 0 ||
+ rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
+
+ rcu_delay_page_cache_fill_msec =
+ clamp(rcu_delay_page_cache_fill_msec, 0,
+ (int) (100 * MSEC_PER_SEC));
+
+ pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
+ rcu_delay_page_cache_fill_msec);
+ }
+
+ for_each_possible_cpu(cpu) {
+ struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
+
+ for (i = 0; i < KFREE_N_BATCHES; i++) {
+ INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
+ krcp->krw_arr[i].krcp = krcp;
+
+ for (j = 0; j < FREE_N_CHANNELS; j++)
+ INIT_LIST_HEAD(&krcp->krw_arr[i].bulk_head_free[j]);
+ }
+
+ for (i = 0; i < FREE_N_CHANNELS; i++)
+ INIT_LIST_HEAD(&krcp->bulk_head[i]);
+
+ INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
+ INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
+ krcp->initialized = true;
+ }
+ if (register_shrinker(&kfree_rcu_shrinker, "rcu-kfree"))
+ pr_err("Failed to register kfree_rcu() shrinker!\n");
+}
+
+void __init rcu_init(void)
+{
+ int cpu = smp_processor_id();
+
+ rcu_early_boot_tests();
+
+ kfree_rcu_batch_init();
+ rcu_bootup_announce();
+ sanitize_kthread_prio();
+ rcu_init_geometry();
+ rcu_init_one();
+ if (dump_tree)
+ rcu_dump_rcu_node_tree();
+ if (use_softirq)
+ open_softirq(RCU_SOFTIRQ, rcu_core_si);
+
+ /*
+ * We don't need protection against CPU-hotplug here because
+ * this is called early in boot, before either interrupts
+ * or the scheduler are operational.
+ */
+ pm_notifier(rcu_pm_notify, 0);
+ WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
+ rcutree_prepare_cpu(cpu);
+ rcu_cpu_starting(cpu);
+ rcutree_online_cpu(cpu);
+
+ /* Create workqueue for Tree SRCU and for expedited GPs. */
+ rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
+ WARN_ON(!rcu_gp_wq);
+ rcu_alloc_par_gp_wq();
+
+ /* Fill in default value for rcutree.qovld boot parameter. */
+ /* -After- the rcu_node ->lock fields are initialized! */
+ if (qovld < 0)
+ qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
+ else
+ qovld_calc = qovld;
+
+ // Kick-start in case any polled grace periods started early.
+ (void)start_poll_synchronize_rcu_expedited();
+
+ rcu_test_sync_prims();
+}
+
+#include "tree_stall.h"
+#include "tree_exp.h"
+#include "tree_nocb.h"
+#include "tree_plugin.h"