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-rw-r--r--kernel/rcu/tree_stall.h1041
1 files changed, 1041 insertions, 0 deletions
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
new file mode 100644
index 000000000..7d15b5b5a
--- /dev/null
+++ b/kernel/rcu/tree_stall.h
@@ -0,0 +1,1041 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * RCU CPU stall warnings for normal RCU grace periods
+ *
+ * Copyright IBM Corporation, 2019
+ *
+ * Author: Paul E. McKenney <paulmck@linux.ibm.com>
+ */
+
+#include <linux/kvm_para.h>
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Controlling CPU stall warnings, including delay calculation.
+
+/* panic() on RCU Stall sysctl. */
+int sysctl_panic_on_rcu_stall __read_mostly;
+int sysctl_max_rcu_stall_to_panic __read_mostly;
+
+#ifdef CONFIG_PROVE_RCU
+#define RCU_STALL_DELAY_DELTA (5 * HZ)
+#else
+#define RCU_STALL_DELAY_DELTA 0
+#endif
+#define RCU_STALL_MIGHT_DIV 8
+#define RCU_STALL_MIGHT_MIN (2 * HZ)
+
+int rcu_exp_jiffies_till_stall_check(void)
+{
+ int cpu_stall_timeout = READ_ONCE(rcu_exp_cpu_stall_timeout);
+ int exp_stall_delay_delta = 0;
+ int till_stall_check;
+
+ // Zero says to use rcu_cpu_stall_timeout, but in milliseconds.
+ if (!cpu_stall_timeout)
+ cpu_stall_timeout = jiffies_to_msecs(rcu_jiffies_till_stall_check());
+
+ // Limit check must be consistent with the Kconfig limits for
+ // CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range.
+ // The minimum clamped value is "2UL", because at least one full
+ // tick has to be guaranteed.
+ till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 21UL * HZ);
+
+ if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout)
+ WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check));
+
+#ifdef CONFIG_PROVE_RCU
+ /* Add extra ~25% out of till_stall_check. */
+ exp_stall_delay_delta = ((till_stall_check * 25) / 100) + 1;
+#endif
+
+ return till_stall_check + exp_stall_delay_delta;
+}
+EXPORT_SYMBOL_GPL(rcu_exp_jiffies_till_stall_check);
+
+/* Limit-check stall timeouts specified at boottime and runtime. */
+int rcu_jiffies_till_stall_check(void)
+{
+ int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
+
+ /*
+ * Limit check must be consistent with the Kconfig limits
+ * for CONFIG_RCU_CPU_STALL_TIMEOUT.
+ */
+ if (till_stall_check < 3) {
+ WRITE_ONCE(rcu_cpu_stall_timeout, 3);
+ till_stall_check = 3;
+ } else if (till_stall_check > 300) {
+ WRITE_ONCE(rcu_cpu_stall_timeout, 300);
+ till_stall_check = 300;
+ }
+ return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
+}
+EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check);
+
+/**
+ * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled?
+ *
+ * Returns @true if the current grace period is sufficiently old that
+ * it is reasonable to assume that it might be stalled. This can be
+ * useful when deciding whether to allocate memory to enable RCU-mediated
+ * freeing on the one hand or just invoking synchronize_rcu() on the other.
+ * The latter is preferable when the grace period is stalled.
+ *
+ * Note that sampling of the .gp_start and .gp_seq fields must be done
+ * carefully to avoid false positives at the beginnings and ends of
+ * grace periods.
+ */
+bool rcu_gp_might_be_stalled(void)
+{
+ unsigned long d = rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV;
+ unsigned long j = jiffies;
+
+ if (d < RCU_STALL_MIGHT_MIN)
+ d = RCU_STALL_MIGHT_MIN;
+ smp_mb(); // jiffies before .gp_seq to avoid false positives.
+ if (!rcu_gp_in_progress())
+ return false;
+ // Long delays at this point avoids false positive, but a delay
+ // of ULONG_MAX/4 jiffies voids your no-false-positive warranty.
+ smp_mb(); // .gp_seq before second .gp_start
+ // And ditto here.
+ return !time_before(j, READ_ONCE(rcu_state.gp_start) + d);
+}
+
+/* Don't do RCU CPU stall warnings during long sysrq printouts. */
+void rcu_sysrq_start(void)
+{
+ if (!rcu_cpu_stall_suppress)
+ rcu_cpu_stall_suppress = 2;
+}
+
+void rcu_sysrq_end(void)
+{
+ if (rcu_cpu_stall_suppress == 2)
+ rcu_cpu_stall_suppress = 0;
+}
+
+/* Don't print RCU CPU stall warnings during a kernel panic. */
+static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
+{
+ rcu_cpu_stall_suppress = 1;
+ return NOTIFY_DONE;
+}
+
+static struct notifier_block rcu_panic_block = {
+ .notifier_call = rcu_panic,
+};
+
+static int __init check_cpu_stall_init(void)
+{
+ atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
+ return 0;
+}
+early_initcall(check_cpu_stall_init);
+
+/* If so specified via sysctl, panic, yielding cleaner stall-warning output. */
+static void panic_on_rcu_stall(void)
+{
+ static int cpu_stall;
+
+ if (++cpu_stall < sysctl_max_rcu_stall_to_panic)
+ return;
+
+ if (sysctl_panic_on_rcu_stall)
+ panic("RCU Stall\n");
+}
+
+/**
+ * rcu_cpu_stall_reset - restart stall-warning timeout for current grace period
+ *
+ * To perform the reset request from the caller, disable stall detection until
+ * 3 fqs loops have passed. This is required to ensure a fresh jiffies is
+ * loaded. It should be safe to do from the fqs loop as enough timer
+ * interrupts and context switches should have passed.
+ *
+ * The caller must disable hard irqs.
+ */
+void rcu_cpu_stall_reset(void)
+{
+ WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, 3);
+ WRITE_ONCE(rcu_state.jiffies_stall, ULONG_MAX);
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Interaction with RCU grace periods
+
+/* Start of new grace period, so record stall time (and forcing times). */
+static void record_gp_stall_check_time(void)
+{
+ unsigned long j = jiffies;
+ unsigned long j1;
+
+ WRITE_ONCE(rcu_state.gp_start, j);
+ j1 = rcu_jiffies_till_stall_check();
+ smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq.
+ WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, 0);
+ WRITE_ONCE(rcu_state.jiffies_stall, j + j1);
+ rcu_state.jiffies_resched = j + j1 / 2;
+ rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs);
+}
+
+/* Zero ->ticks_this_gp and snapshot the number of RCU softirq handlers. */
+static void zero_cpu_stall_ticks(struct rcu_data *rdp)
+{
+ rdp->ticks_this_gp = 0;
+ rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
+ WRITE_ONCE(rdp->last_fqs_resched, jiffies);
+}
+
+/*
+ * If too much time has passed in the current grace period, and if
+ * so configured, go kick the relevant kthreads.
+ */
+static void rcu_stall_kick_kthreads(void)
+{
+ unsigned long j;
+
+ if (!READ_ONCE(rcu_kick_kthreads))
+ return;
+ j = READ_ONCE(rcu_state.jiffies_kick_kthreads);
+ if (time_after(jiffies, j) && rcu_state.gp_kthread &&
+ (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) {
+ WARN_ONCE(1, "Kicking %s grace-period kthread\n",
+ rcu_state.name);
+ rcu_ftrace_dump(DUMP_ALL);
+ wake_up_process(rcu_state.gp_kthread);
+ WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ);
+ }
+}
+
+/*
+ * Handler for the irq_work request posted about halfway into the RCU CPU
+ * stall timeout, and used to detect excessive irq disabling. Set state
+ * appropriately, but just complain if there is unexpected state on entry.
+ */
+static void rcu_iw_handler(struct irq_work *iwp)
+{
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+
+ rdp = container_of(iwp, struct rcu_data, rcu_iw);
+ rnp = rdp->mynode;
+ raw_spin_lock_rcu_node(rnp);
+ if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
+ rdp->rcu_iw_gp_seq = rnp->gp_seq;
+ rdp->rcu_iw_pending = false;
+ }
+ raw_spin_unlock_rcu_node(rnp);
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// Printing RCU CPU stall warnings
+
+#ifdef CONFIG_PREEMPT_RCU
+
+/*
+ * Dump detailed information for all tasks blocking the current RCU
+ * grace period on the specified rcu_node structure.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+ unsigned long flags;
+ struct task_struct *t;
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ t = list_entry(rnp->gp_tasks->prev,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ /*
+ * We could be printing a lot while holding a spinlock.
+ * Avoid triggering hard lockup.
+ */
+ touch_nmi_watchdog();
+ sched_show_task(t);
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
+// Communicate task state back to the RCU CPU stall warning request.
+struct rcu_stall_chk_rdr {
+ int nesting;
+ union rcu_special rs;
+ bool on_blkd_list;
+};
+
+/*
+ * Report out the state of a not-running task that is stalling the
+ * current RCU grace period.
+ */
+static int check_slow_task(struct task_struct *t, void *arg)
+{
+ struct rcu_stall_chk_rdr *rscrp = arg;
+
+ if (task_curr(t))
+ return -EBUSY; // It is running, so decline to inspect it.
+ rscrp->nesting = t->rcu_read_lock_nesting;
+ rscrp->rs = t->rcu_read_unlock_special;
+ rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry);
+ return 0;
+}
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each of the first few of them.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ int i = 0;
+ int ndetected = 0;
+ struct rcu_stall_chk_rdr rscr;
+ struct task_struct *t;
+ struct task_struct *ts[8];
+
+ lockdep_assert_irqs_disabled();
+ if (!rcu_preempt_blocked_readers_cgp(rnp)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return 0;
+ }
+ pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
+ rnp->level, rnp->grplo, rnp->grphi);
+ t = list_entry(rnp->gp_tasks->prev,
+ struct task_struct, rcu_node_entry);
+ list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+ get_task_struct(t);
+ ts[i++] = t;
+ if (i >= ARRAY_SIZE(ts))
+ break;
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ while (i) {
+ t = ts[--i];
+ if (task_call_func(t, check_slow_task, &rscr))
+ pr_cont(" P%d", t->pid);
+ else
+ pr_cont(" P%d/%d:%c%c%c%c",
+ t->pid, rscr.nesting,
+ ".b"[rscr.rs.b.blocked],
+ ".q"[rscr.rs.b.need_qs],
+ ".e"[rscr.rs.b.exp_hint],
+ ".l"[rscr.on_blkd_list]);
+ lockdep_assert_irqs_disabled();
+ put_task_struct(t);
+ ndetected++;
+ }
+ pr_cont("\n");
+ return ndetected;
+}
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
+{
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections.
+ */
+static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return 0;
+}
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+/*
+ * Dump stacks of all tasks running on stalled CPUs. First try using
+ * NMIs, but fall back to manual remote stack tracing on architectures
+ * that don't support NMI-based stack dumps. The NMI-triggered stack
+ * traces are more accurate because they are printed by the target CPU.
+ */
+static void rcu_dump_cpu_stacks(void)
+{
+ int cpu;
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ rcu_for_each_leaf_node(rnp) {
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ for_each_leaf_node_possible_cpu(rnp, cpu)
+ if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+ if (cpu_is_offline(cpu))
+ pr_err("Offline CPU %d blocking current GP.\n", cpu);
+ else
+ dump_cpu_task(cpu);
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+}
+
+static const char * const gp_state_names[] = {
+ [RCU_GP_IDLE] = "RCU_GP_IDLE",
+ [RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS",
+ [RCU_GP_DONE_GPS] = "RCU_GP_DONE_GPS",
+ [RCU_GP_ONOFF] = "RCU_GP_ONOFF",
+ [RCU_GP_INIT] = "RCU_GP_INIT",
+ [RCU_GP_WAIT_FQS] = "RCU_GP_WAIT_FQS",
+ [RCU_GP_DOING_FQS] = "RCU_GP_DOING_FQS",
+ [RCU_GP_CLEANUP] = "RCU_GP_CLEANUP",
+ [RCU_GP_CLEANED] = "RCU_GP_CLEANED",
+};
+
+/*
+ * Convert a ->gp_state value to a character string.
+ */
+static const char *gp_state_getname(short gs)
+{
+ if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
+ return "???";
+ return gp_state_names[gs];
+}
+
+/* Is the RCU grace-period kthread being starved of CPU time? */
+static bool rcu_is_gp_kthread_starving(unsigned long *jp)
+{
+ unsigned long j = jiffies - READ_ONCE(rcu_state.gp_activity);
+
+ if (jp)
+ *jp = j;
+ return j > 2 * HZ;
+}
+
+static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp)
+{
+ int cpu;
+ struct task_struct *rcuc;
+ unsigned long j;
+
+ rcuc = rdp->rcu_cpu_kthread_task;
+ if (!rcuc)
+ return false;
+
+ cpu = task_cpu(rcuc);
+ if (cpu_is_offline(cpu) || idle_cpu(cpu))
+ return false;
+
+ j = jiffies - READ_ONCE(rdp->rcuc_activity);
+
+ if (jp)
+ *jp = j;
+ return j > 2 * HZ;
+}
+
+/*
+ * Print out diagnostic information for the specified stalled CPU.
+ *
+ * If the specified CPU is aware of the current RCU grace period, then
+ * print the number of scheduling clock interrupts the CPU has taken
+ * during the time that it has been aware. Otherwise, print the number
+ * of RCU grace periods that this CPU is ignorant of, for example, "1"
+ * if the CPU was aware of the previous grace period.
+ *
+ * Also print out idle info.
+ */
+static void print_cpu_stall_info(int cpu)
+{
+ unsigned long delta;
+ bool falsepositive;
+ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+ char *ticks_title;
+ unsigned long ticks_value;
+ bool rcuc_starved;
+ unsigned long j;
+ char buf[32];
+
+ /*
+ * We could be printing a lot while holding a spinlock. Avoid
+ * triggering hard lockup.
+ */
+ touch_nmi_watchdog();
+
+ ticks_value = rcu_seq_ctr(rcu_state.gp_seq - rdp->gp_seq);
+ if (ticks_value) {
+ ticks_title = "GPs behind";
+ } else {
+ ticks_title = "ticks this GP";
+ ticks_value = rdp->ticks_this_gp;
+ }
+ delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
+ falsepositive = rcu_is_gp_kthread_starving(NULL) &&
+ rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
+ rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
+ if (rcuc_starved)
+ sprintf(buf, " rcuc=%ld jiffies(starved)", j);
+ pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
+ cpu,
+ "O."[!!cpu_online(cpu)],
+ "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
+ "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
+ !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
+ rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
+ "!."[!delta],
+ ticks_value, ticks_title,
+ rcu_dynticks_snap(cpu) & 0xffff,
+ ct_dynticks_nesting_cpu(cpu), ct_dynticks_nmi_nesting_cpu(cpu),
+ rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
+ data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
+ rcuc_starved ? buf : "",
+ falsepositive ? " (false positive?)" : "");
+}
+
+/* Complain about starvation of grace-period kthread. */
+static void rcu_check_gp_kthread_starvation(void)
+{
+ int cpu;
+ struct task_struct *gpk = rcu_state.gp_kthread;
+ unsigned long j;
+
+ if (rcu_is_gp_kthread_starving(&j)) {
+ cpu = gpk ? task_cpu(gpk) : -1;
+ pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x ->cpu=%d\n",
+ rcu_state.name, j,
+ (long)rcu_seq_current(&rcu_state.gp_seq),
+ data_race(READ_ONCE(rcu_state.gp_flags)),
+ gp_state_getname(rcu_state.gp_state),
+ data_race(READ_ONCE(rcu_state.gp_state)),
+ gpk ? data_race(READ_ONCE(gpk->__state)) : ~0, cpu);
+ if (gpk) {
+ pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
+ pr_err("RCU grace-period kthread stack dump:\n");
+ sched_show_task(gpk);
+ if (cpu >= 0) {
+ if (cpu_is_offline(cpu)) {
+ pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
+ } else {
+ pr_err("Stack dump where RCU GP kthread last ran:\n");
+ dump_cpu_task(cpu);
+ }
+ }
+ wake_up_process(gpk);
+ }
+ }
+}
+
+/* Complain about missing wakeups from expired fqs wait timer */
+static void rcu_check_gp_kthread_expired_fqs_timer(void)
+{
+ struct task_struct *gpk = rcu_state.gp_kthread;
+ short gp_state;
+ unsigned long jiffies_fqs;
+ int cpu;
+
+ /*
+ * Order reads of .gp_state and .jiffies_force_qs.
+ * Matching smp_wmb() is present in rcu_gp_fqs_loop().
+ */
+ gp_state = smp_load_acquire(&rcu_state.gp_state);
+ jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs);
+
+ if (gp_state == RCU_GP_WAIT_FQS &&
+ time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) &&
+ gpk && !READ_ONCE(gpk->on_rq)) {
+ cpu = task_cpu(gpk);
+ pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x\n",
+ rcu_state.name, (jiffies - jiffies_fqs),
+ (long)rcu_seq_current(&rcu_state.gp_seq),
+ data_race(rcu_state.gp_flags),
+ gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS,
+ data_race(READ_ONCE(gpk->__state)));
+ pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n",
+ cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu));
+ }
+}
+
+static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
+{
+ int cpu;
+ unsigned long flags;
+ unsigned long gpa;
+ unsigned long j;
+ int ndetected = 0;
+ struct rcu_node *rnp;
+ long totqlen = 0;
+
+ lockdep_assert_irqs_disabled();
+
+ /* Kick and suppress, if so configured. */
+ rcu_stall_kick_kthreads();
+ if (rcu_stall_is_suppressed())
+ return;
+
+ /*
+ * OK, time to rat on our buddy...
+ * See Documentation/RCU/stallwarn.rst for info on how to debug
+ * RCU CPU stall warnings.
+ */
+ trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected"));
+ pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name);
+ rcu_for_each_leaf_node(rnp) {
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (rnp->qsmask != 0) {
+ for_each_leaf_node_possible_cpu(rnp, cpu)
+ if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
+ print_cpu_stall_info(cpu);
+ ndetected++;
+ }
+ }
+ ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock.
+ lockdep_assert_irqs_disabled();
+ }
+
+ for_each_possible_cpu(cpu)
+ totqlen += rcu_get_n_cbs_cpu(cpu);
+ pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n",
+ smp_processor_id(), (long)(jiffies - gps),
+ (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
+ if (ndetected) {
+ rcu_dump_cpu_stacks();
+
+ /* Complain about tasks blocking the grace period. */
+ rcu_for_each_leaf_node(rnp)
+ rcu_print_detail_task_stall_rnp(rnp);
+ } else {
+ if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) {
+ pr_err("INFO: Stall ended before state dump start\n");
+ } else {
+ j = jiffies;
+ gpa = data_race(READ_ONCE(rcu_state.gp_activity));
+ pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
+ rcu_state.name, j - gpa, j, gpa,
+ data_race(READ_ONCE(jiffies_till_next_fqs)),
+ data_race(READ_ONCE(rcu_get_root()->qsmask)));
+ }
+ }
+ /* Rewrite if needed in case of slow consoles. */
+ if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
+ WRITE_ONCE(rcu_state.jiffies_stall,
+ jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
+
+ rcu_check_gp_kthread_expired_fqs_timer();
+ rcu_check_gp_kthread_starvation();
+
+ panic_on_rcu_stall();
+
+ rcu_force_quiescent_state(); /* Kick them all. */
+}
+
+static void print_cpu_stall(unsigned long gps)
+{
+ int cpu;
+ unsigned long flags;
+ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+ struct rcu_node *rnp = rcu_get_root();
+ long totqlen = 0;
+
+ lockdep_assert_irqs_disabled();
+
+ /* Kick and suppress, if so configured. */
+ rcu_stall_kick_kthreads();
+ if (rcu_stall_is_suppressed())
+ return;
+
+ /*
+ * OK, time to rat on ourselves...
+ * See Documentation/RCU/stallwarn.rst for info on how to debug
+ * RCU CPU stall warnings.
+ */
+ trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected"));
+ pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
+ raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
+ print_cpu_stall_info(smp_processor_id());
+ raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
+ for_each_possible_cpu(cpu)
+ totqlen += rcu_get_n_cbs_cpu(cpu);
+ pr_cont("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n",
+ jiffies - gps,
+ (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus);
+
+ rcu_check_gp_kthread_expired_fqs_timer();
+ rcu_check_gp_kthread_starvation();
+
+ rcu_dump_cpu_stacks();
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ /* Rewrite if needed in case of slow consoles. */
+ if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall)))
+ WRITE_ONCE(rcu_state.jiffies_stall,
+ jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+ panic_on_rcu_stall();
+
+ /*
+ * Attempt to revive the RCU machinery by forcing a context switch.
+ *
+ * A context switch would normally allow the RCU state machine to make
+ * progress and it could be we're stuck in kernel space without context
+ * switches for an entirely unreasonable amount of time.
+ */
+ set_tsk_need_resched(current);
+ set_preempt_need_resched();
+}
+
+static void check_cpu_stall(struct rcu_data *rdp)
+{
+ bool didstall = false;
+ unsigned long gs1;
+ unsigned long gs2;
+ unsigned long gps;
+ unsigned long j;
+ unsigned long jn;
+ unsigned long js;
+ struct rcu_node *rnp;
+
+ lockdep_assert_irqs_disabled();
+ if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) ||
+ !rcu_gp_in_progress())
+ return;
+ rcu_stall_kick_kthreads();
+
+ /*
+ * Check if it was requested (via rcu_cpu_stall_reset()) that the FQS
+ * loop has to set jiffies to ensure a non-stale jiffies value. This
+ * is required to have good jiffies value after coming out of long
+ * breaks of jiffies updates. Not doing so can cause false positives.
+ */
+ if (READ_ONCE(rcu_state.nr_fqs_jiffies_stall) > 0)
+ return;
+
+ j = jiffies;
+
+ /*
+ * Lots of memory barriers to reject false positives.
+ *
+ * The idea is to pick up rcu_state.gp_seq, then
+ * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally
+ * another copy of rcu_state.gp_seq. These values are updated in
+ * the opposite order with memory barriers (or equivalent) during
+ * grace-period initialization and cleanup. Now, a false positive
+ * can occur if we get an new value of rcu_state.gp_start and a old
+ * value of rcu_state.jiffies_stall. But given the memory barriers,
+ * the only way that this can happen is if one grace period ends
+ * and another starts between these two fetches. This is detected
+ * by comparing the second fetch of rcu_state.gp_seq with the
+ * previous fetch from rcu_state.gp_seq.
+ *
+ * Given this check, comparisons of jiffies, rcu_state.jiffies_stall,
+ * and rcu_state.gp_start suffice to forestall false positives.
+ */
+ gs1 = READ_ONCE(rcu_state.gp_seq);
+ smp_rmb(); /* Pick up ->gp_seq first... */
+ js = READ_ONCE(rcu_state.jiffies_stall);
+ smp_rmb(); /* ...then ->jiffies_stall before the rest... */
+ gps = READ_ONCE(rcu_state.gp_start);
+ smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
+ gs2 = READ_ONCE(rcu_state.gp_seq);
+ if (gs1 != gs2 ||
+ ULONG_CMP_LT(j, js) ||
+ ULONG_CMP_GE(gps, js))
+ return; /* No stall or GP completed since entering function. */
+ rnp = rdp->mynode;
+ jn = jiffies + ULONG_MAX / 2;
+ if (rcu_gp_in_progress() &&
+ (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
+ cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
+
+ /*
+ * If a virtual machine is stopped by the host it can look to
+ * the watchdog like an RCU stall. Check to see if the host
+ * stopped the vm.
+ */
+ if (kvm_check_and_clear_guest_paused())
+ return;
+
+ /* We haven't checked in, so go dump stack. */
+ print_cpu_stall(gps);
+ if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
+ rcu_ftrace_dump(DUMP_ALL);
+ didstall = true;
+
+ } else if (rcu_gp_in_progress() &&
+ ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
+ cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) {
+
+ /*
+ * If a virtual machine is stopped by the host it can look to
+ * the watchdog like an RCU stall. Check to see if the host
+ * stopped the vm.
+ */
+ if (kvm_check_and_clear_guest_paused())
+ return;
+
+ /* They had a few time units to dump stack, so complain. */
+ print_other_cpu_stall(gs2, gps);
+ if (READ_ONCE(rcu_cpu_stall_ftrace_dump))
+ rcu_ftrace_dump(DUMP_ALL);
+ didstall = true;
+ }
+ if (didstall && READ_ONCE(rcu_state.jiffies_stall) == jn) {
+ jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
+ WRITE_ONCE(rcu_state.jiffies_stall, jn);
+ }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+//
+// RCU forward-progress mechanisms, including of callback invocation.
+
+
+/*
+ * Check to see if a failure to end RCU priority inversion was due to
+ * a CPU not passing through a quiescent state. When this happens, there
+ * is nothing that RCU priority boosting can do to help, so we shouldn't
+ * count this as an RCU priority boosting failure. A return of true says
+ * RCU priority boosting is to blame, and false says otherwise. If false
+ * is returned, the first of the CPUs to blame is stored through cpup.
+ * If there was no CPU blocking the current grace period, but also nothing
+ * in need of being boosted, *cpup is set to -1. This can happen in case
+ * of vCPU preemption while the last CPU is reporting its quiscent state,
+ * for example.
+ *
+ * If cpup is NULL, then a lockless quick check is carried out, suitable
+ * for high-rate usage. On the other hand, if cpup is non-NULL, each
+ * rcu_node structure's ->lock is acquired, ruling out high-rate usage.
+ */
+bool rcu_check_boost_fail(unsigned long gp_state, int *cpup)
+{
+ bool atb = false;
+ int cpu;
+ unsigned long flags;
+ struct rcu_node *rnp;
+
+ rcu_for_each_leaf_node(rnp) {
+ if (!cpup) {
+ if (data_race(READ_ONCE(rnp->qsmask))) {
+ return false;
+ } else {
+ if (READ_ONCE(rnp->gp_tasks))
+ atb = true;
+ continue;
+ }
+ }
+ *cpup = -1;
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ if (rnp->gp_tasks)
+ atb = true;
+ if (!rnp->qsmask) {
+ // No CPUs without quiescent states for this rnp.
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ continue;
+ }
+ // Find the first holdout CPU.
+ for_each_leaf_node_possible_cpu(rnp, cpu) {
+ if (rnp->qsmask & (1UL << (cpu - rnp->grplo))) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ *cpup = cpu;
+ return false;
+ }
+ }
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ }
+ // Can't blame CPUs, so must blame RCU priority boosting.
+ return atb;
+}
+EXPORT_SYMBOL_GPL(rcu_check_boost_fail);
+
+/*
+ * Show the state of the grace-period kthreads.
+ */
+void show_rcu_gp_kthreads(void)
+{
+ unsigned long cbs = 0;
+ int cpu;
+ unsigned long j;
+ unsigned long ja;
+ unsigned long jr;
+ unsigned long js;
+ unsigned long jw;
+ struct rcu_data *rdp;
+ struct rcu_node *rnp;
+ struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
+
+ j = jiffies;
+ ja = j - data_race(READ_ONCE(rcu_state.gp_activity));
+ jr = j - data_race(READ_ONCE(rcu_state.gp_req_activity));
+ js = j - data_race(READ_ONCE(rcu_state.gp_start));
+ jw = j - data_race(READ_ONCE(rcu_state.gp_wake_time));
+ pr_info("%s: wait state: %s(%d) ->state: %#x ->rt_priority %u delta ->gp_start %lu ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_max %lu ->gp_flags %#x\n",
+ rcu_state.name, gp_state_getname(rcu_state.gp_state),
+ data_race(READ_ONCE(rcu_state.gp_state)),
+ t ? data_race(READ_ONCE(t->__state)) : 0x1ffff, t ? t->rt_priority : 0xffU,
+ js, ja, jr, jw, (long)data_race(READ_ONCE(rcu_state.gp_wake_seq)),
+ (long)data_race(READ_ONCE(rcu_state.gp_seq)),
+ (long)data_race(READ_ONCE(rcu_get_root()->gp_seq_needed)),
+ data_race(READ_ONCE(rcu_state.gp_max)),
+ data_race(READ_ONCE(rcu_state.gp_flags)));
+ rcu_for_each_node_breadth_first(rnp) {
+ if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rnp->gp_seq_needed)) &&
+ !data_race(READ_ONCE(rnp->qsmask)) && !data_race(READ_ONCE(rnp->boost_tasks)) &&
+ !data_race(READ_ONCE(rnp->exp_tasks)) && !data_race(READ_ONCE(rnp->gp_tasks)))
+ continue;
+ pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n",
+ rnp->grplo, rnp->grphi,
+ (long)data_race(READ_ONCE(rnp->gp_seq)),
+ (long)data_race(READ_ONCE(rnp->gp_seq_needed)),
+ data_race(READ_ONCE(rnp->qsmask)),
+ ".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))],
+ ".B"[!!data_race(READ_ONCE(rnp->boost_tasks))],
+ ".E"[!!data_race(READ_ONCE(rnp->exp_tasks))],
+ ".G"[!!data_race(READ_ONCE(rnp->gp_tasks))],
+ data_race(READ_ONCE(rnp->n_boosts)));
+ if (!rcu_is_leaf_node(rnp))
+ continue;
+ for_each_leaf_node_possible_cpu(rnp, cpu) {
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ if (READ_ONCE(rdp->gpwrap) ||
+ ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
+ READ_ONCE(rdp->gp_seq_needed)))
+ continue;
+ pr_info("\tcpu %d ->gp_seq_needed %ld\n",
+ cpu, (long)data_race(READ_ONCE(rdp->gp_seq_needed)));
+ }
+ }
+ for_each_possible_cpu(cpu) {
+ rdp = per_cpu_ptr(&rcu_data, cpu);
+ cbs += data_race(READ_ONCE(rdp->n_cbs_invoked));
+ if (rcu_segcblist_is_offloaded(&rdp->cblist))
+ show_rcu_nocb_state(rdp);
+ }
+ pr_info("RCU callbacks invoked since boot: %lu\n", cbs);
+ show_rcu_tasks_gp_kthreads();
+}
+EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
+
+/*
+ * This function checks for grace-period requests that fail to motivate
+ * RCU to come out of its idle mode.
+ */
+static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp,
+ const unsigned long gpssdelay)
+{
+ unsigned long flags;
+ unsigned long j;
+ struct rcu_node *rnp_root = rcu_get_root();
+ static atomic_t warned = ATOMIC_INIT(0);
+
+ if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() ||
+ ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
+ READ_ONCE(rnp_root->gp_seq_needed)) ||
+ !smp_load_acquire(&rcu_state.gp_kthread)) // Get stable kthread.
+ return;
+ j = jiffies; /* Expensive access, and in common case don't get here. */
+ if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
+ time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
+ atomic_read(&warned))
+ return;
+
+ raw_spin_lock_irqsave_rcu_node(rnp, flags);
+ j = jiffies;
+ if (rcu_gp_in_progress() ||
+ ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
+ READ_ONCE(rnp_root->gp_seq_needed)) ||
+ time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
+ time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
+ atomic_read(&warned)) {
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ /* Hold onto the leaf lock to make others see warned==1. */
+
+ if (rnp_root != rnp)
+ raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
+ j = jiffies;
+ if (rcu_gp_in_progress() ||
+ ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq),
+ READ_ONCE(rnp_root->gp_seq_needed)) ||
+ time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) ||
+ time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) ||
+ atomic_xchg(&warned, 1)) {
+ if (rnp_root != rnp)
+ /* irqs remain disabled. */
+ raw_spin_unlock_rcu_node(rnp_root);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ return;
+ }
+ WARN_ON(1);
+ if (rnp_root != rnp)
+ raw_spin_unlock_rcu_node(rnp_root);
+ raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+ show_rcu_gp_kthreads();
+}
+
+/*
+ * Do a forward-progress check for rcutorture. This is normally invoked
+ * due to an OOM event. The argument "j" gives the time period during
+ * which rcutorture would like progress to have been made.
+ */
+void rcu_fwd_progress_check(unsigned long j)
+{
+ unsigned long cbs;
+ int cpu;
+ unsigned long max_cbs = 0;
+ int max_cpu = -1;
+ struct rcu_data *rdp;
+
+ if (rcu_gp_in_progress()) {
+ pr_info("%s: GP age %lu jiffies\n",
+ __func__, jiffies - data_race(READ_ONCE(rcu_state.gp_start)));
+ show_rcu_gp_kthreads();
+ } else {
+ pr_info("%s: Last GP end %lu jiffies ago\n",
+ __func__, jiffies - data_race(READ_ONCE(rcu_state.gp_end)));
+ preempt_disable();
+ rdp = this_cpu_ptr(&rcu_data);
+ rcu_check_gp_start_stall(rdp->mynode, rdp, j);
+ preempt_enable();
+ }
+ for_each_possible_cpu(cpu) {
+ cbs = rcu_get_n_cbs_cpu(cpu);
+ if (!cbs)
+ continue;
+ if (max_cpu < 0)
+ pr_info("%s: callbacks", __func__);
+ pr_cont(" %d: %lu", cpu, cbs);
+ if (cbs <= max_cbs)
+ continue;
+ max_cbs = cbs;
+ max_cpu = cpu;
+ }
+ if (max_cpu >= 0)
+ pr_cont("\n");
+}
+EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
+
+/* Commandeer a sysrq key to dump RCU's tree. */
+static bool sysrq_rcu;
+module_param(sysrq_rcu, bool, 0444);
+
+/* Dump grace-period-request information due to commandeered sysrq. */
+static void sysrq_show_rcu(int key)
+{
+ show_rcu_gp_kthreads();
+}
+
+static const struct sysrq_key_op sysrq_rcudump_op = {
+ .handler = sysrq_show_rcu,
+ .help_msg = "show-rcu(y)",
+ .action_msg = "Show RCU tree",
+ .enable_mask = SYSRQ_ENABLE_DUMP,
+};
+
+static int __init rcu_sysrq_init(void)
+{
+ if (sysrq_rcu)
+ return register_sysrq_key('y', &sysrq_rcudump_op);
+ return 0;
+}
+early_initcall(rcu_sysrq_init);