Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1304 insertions, 0 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
new file mode 100644
index 000000000..044026abf
--- /dev/null
+++ b/kernel/rcu/tree_plugin.h
@@ -0,0 +1,1304 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Read-Copy Update mechanism for mutual exclusion (tree-based version)
+ * Internal non-public definitions that provide either classic
+ * or preemptible semantics.
+ *
+ * Copyright Red Hat, 2009
+ * Copyright IBM Corporation, 2009
+ *
+ * Author: Ingo Molnar <mingo@elte.hu>
+ *	   Paul E. McKenney <paulmck@linux.ibm.com>
+ */
+
+#include "../locking/rtmutex_common.h"
+
+static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
+{
+	/*
+	 * In order to read the offloaded state of an rdp in a safe
+	 * and stable way and prevent from its value to be changed
+	 * under us, we must either hold the barrier mutex, the cpu
+	 * hotplug lock (read or write) or the nocb lock. Local
+	 * non-preemptible reads are also safe. NOCB kthreads and
+	 * timers have their own means of synchronization against the
+	 * offloaded state updaters.
+	 */
+	RCU_LOCKDEP_WARN(
+		!(lockdep_is_held(&rcu_state.barrier_mutex) ||
+		  (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
+		  rcu_lockdep_is_held_nocb(rdp) ||
+		  (rdp == this_cpu_ptr(&rcu_data) &&
+		   !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
+		  rcu_current_is_nocb_kthread(rdp)),
+		"Unsafe read of RCU_NOCB offloaded state"
+	);
+
+	return rcu_segcblist_is_offloaded(&rdp->cblist);
+}
+
+/*
+ * Check the RCU kernel configuration parameters and print informative
+ * messages about anything out of the ordinary.
+ */
+static void __init rcu_bootup_announce_oddness(void)
+{
+	if (IS_ENABLED(CONFIG_RCU_TRACE))
+		pr_info("\tRCU event tracing is enabled.\n");
+	if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
+	    (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
+		pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
+			RCU_FANOUT);
+	if (rcu_fanout_exact)
+		pr_info("\tHierarchical RCU autobalancing is disabled.\n");
+	if (IS_ENABLED(CONFIG_PROVE_RCU))
+		pr_info("\tRCU lockdep checking is enabled.\n");
+	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+		pr_info("\tRCU strict (and thus non-scalable) grace periods are enabled.\n");
+	if (RCU_NUM_LVLS >= 4)
+		pr_info("\tFour(or more)-level hierarchy is enabled.\n");
+	if (RCU_FANOUT_LEAF != 16)
+		pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
+			RCU_FANOUT_LEAF);
+	if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
+		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
+			rcu_fanout_leaf);
+	if (nr_cpu_ids != NR_CPUS)
+		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
+#ifdef CONFIG_RCU_BOOST
+	pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
+		kthread_prio, CONFIG_RCU_BOOST_DELAY);
+#endif
+	if (blimit != DEFAULT_RCU_BLIMIT)
+		pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
+	if (qhimark != DEFAULT_RCU_QHIMARK)
+		pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
+	if (qlowmark != DEFAULT_RCU_QLOMARK)
+		pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
+	if (qovld != DEFAULT_RCU_QOVLD)
+		pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld);
+	if (jiffies_till_first_fqs != ULONG_MAX)
+		pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
+	if (jiffies_till_next_fqs != ULONG_MAX)
+		pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
+	if (jiffies_till_sched_qs != ULONG_MAX)
+		pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
+	if (rcu_kick_kthreads)
+		pr_info("\tKick kthreads if too-long grace period.\n");
+	if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
+		pr_info("\tRCU callback double-/use-after-free debug is enabled.\n");
+	if (gp_preinit_delay)
+		pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
+	if (gp_init_delay)
+		pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
+	if (gp_cleanup_delay)
+		pr_info("\tRCU debug GP cleanup slowdown %d jiffies.\n", gp_cleanup_delay);
+	if (!use_softirq)
+		pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
+	if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
+		pr_info("\tRCU debug extended QS entry/exit.\n");
+	rcupdate_announce_bootup_oddness();
+}
+
+#ifdef CONFIG_PREEMPT_RCU
+
+static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
+static void rcu_read_unlock_special(struct task_struct *t);
+
+/*
+ * Tell them what RCU they are running.
+ */
+static void __init rcu_bootup_announce(void)
+{
+	pr_info("Preemptible hierarchical RCU implementation.\n");
+	rcu_bootup_announce_oddness();
+}
+
+/* Flags for rcu_preempt_ctxt_queue() decision table. */
+#define RCU_GP_TASKS	0x8
+#define RCU_EXP_TASKS	0x4
+#define RCU_GP_BLKD	0x2
+#define RCU_EXP_BLKD	0x1
+
+/*
+ * Queues a task preempted within an RCU-preempt read-side critical
+ * section into the appropriate location within the ->blkd_tasks list,
+ * depending on the states of any ongoing normal and expedited grace
+ * periods.  The ->gp_tasks pointer indicates which element the normal
+ * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
+ * indicates which element the expedited grace period is waiting on (again,
+ * NULL if none).  If a grace period is waiting on a given element in the
+ * ->blkd_tasks list, it also waits on all subsequent elements.  Thus,
+ * adding a task to the tail of the list blocks any grace period that is
+ * already waiting on one of the elements.  In contrast, adding a task
+ * to the head of the list won't block any grace period that is already
+ * waiting on one of the elements.
+ *
+ * This queuing is imprecise, and can sometimes make an ongoing grace
+ * period wait for a task that is not strictly speaking blocking it.
+ * Given the choice, we needlessly block a normal grace period rather than
+ * blocking an expedited grace period.
+ *
+ * Note that an endless sequence of expedited grace periods still cannot
+ * indefinitely postpone a normal grace period.  Eventually, all of the
+ * fixed number of preempted tasks blocking the normal grace period that are
+ * not also blocking the expedited grace period will resume and complete
+ * their RCU read-side critical sections.  At that point, the ->gp_tasks
+ * pointer will equal the ->exp_tasks pointer, at which point the end of
+ * the corresponding expedited grace period will also be the end of the
+ * normal grace period.
+ */
+static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
+	__releases(rnp->lock) /* But leaves rrupts disabled. */
+{
+	int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
+			 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
+			 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
+			 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
+	struct task_struct *t = current;
+
+	raw_lockdep_assert_held_rcu_node(rnp);
+	WARN_ON_ONCE(rdp->mynode != rnp);
+	WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
+	/* RCU better not be waiting on newly onlined CPUs! */
+	WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
+		     rdp->grpmask);
+
+	/*
+	 * Decide where to queue the newly blocked task.  In theory,
+	 * this could be an if-statement.  In practice, when I tried
+	 * that, it was quite messy.
+	 */
+	switch (blkd_state) {
+	case 0:
+	case                RCU_EXP_TASKS:
+	case                RCU_EXP_TASKS + RCU_GP_BLKD:
+	case RCU_GP_TASKS:
+	case RCU_GP_TASKS + RCU_EXP_TASKS:
+
+		/*
+		 * Blocking neither GP, or first task blocking the normal
+		 * GP but not blocking the already-waiting expedited GP.
+		 * Queue at the head of the list to avoid unnecessarily
+		 * blocking the already-waiting GPs.
+		 */
+		list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
+		break;
+
+	case                                              RCU_EXP_BLKD:
+	case                                RCU_GP_BLKD:
+	case                                RCU_GP_BLKD + RCU_EXP_BLKD:
+	case RCU_GP_TASKS +                               RCU_EXP_BLKD:
+	case RCU_GP_TASKS +                 RCU_GP_BLKD + RCU_EXP_BLKD:
+	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
+
+		/*
+		 * First task arriving that blocks either GP, or first task
+		 * arriving that blocks the expedited GP (with the normal
+		 * GP already waiting), or a task arriving that blocks
+		 * both GPs with both GPs already waiting.  Queue at the
+		 * tail of the list to avoid any GP waiting on any of the
+		 * already queued tasks that are not blocking it.
+		 */
+		list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
+		break;
+
+	case                RCU_EXP_TASKS +               RCU_EXP_BLKD:
+	case                RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
+	case RCU_GP_TASKS + RCU_EXP_TASKS +               RCU_EXP_BLKD:
+
+		/*
+		 * Second or subsequent task blocking the expedited GP.
+		 * The task either does not block the normal GP, or is the
+		 * first task blocking the normal GP.  Queue just after
+		 * the first task blocking the expedited GP.
+		 */
+		list_add(&t->rcu_node_entry, rnp->exp_tasks);
+		break;
+
+	case RCU_GP_TASKS +                 RCU_GP_BLKD:
+	case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
+
+		/*
+		 * Second or subsequent task blocking the normal GP.
+		 * The task does not block the expedited GP. Queue just
+		 * after the first task blocking the normal GP.
+		 */
+		list_add(&t->rcu_node_entry, rnp->gp_tasks);
+		break;
+
+	default:
+
+		/* Yet another exercise in excessive paranoia. */
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	/*
+	 * We have now queued the task.  If it was the first one to
+	 * block either grace period, update the ->gp_tasks and/or
+	 * ->exp_tasks pointers, respectively, to reference the newly
+	 * blocked tasks.
+	 */
+	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
+		WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
+		WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
+	}
+	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
+		WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry);
+	WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
+		     !(rnp->qsmask & rdp->grpmask));
+	WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
+		     !(rnp->expmask & rdp->grpmask));
+	raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
+
+	/*
+	 * Report the quiescent state for the expedited GP.  This expedited
+	 * GP should not be able to end until we report, so there should be
+	 * no need to check for a subsequent expedited GP.  (Though we are
+	 * still in a quiescent state in any case.)
+	 *
+	 * Interrupts are disabled, so ->cpu_no_qs.b.exp cannot change.
+	 */
+	if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp)
+		rcu_report_exp_rdp(rdp);
+	else
+		WARN_ON_ONCE(rdp->cpu_no_qs.b.exp);
+}
+
+/*
+ * Record a preemptible-RCU quiescent state for the specified CPU.
+ * Note that this does not necessarily mean that the task currently running
+ * on the CPU is in a quiescent state:  Instead, it means that the current
+ * grace period need not wait on any RCU read-side critical section that
+ * starts later on this CPU.  It also means that if the current task is
+ * in an RCU read-side critical section, it has already added itself to
+ * some leaf rcu_node structure's ->blkd_tasks list.  In addition to the
+ * current task, there might be any number of other tasks blocked while
+ * in an RCU read-side critical section.
+ *
+ * Unlike non-preemptible-RCU, quiescent state reports for expedited
+ * grace periods are handled separately via deferred quiescent states
+ * and context switch events.
+ *
+ * Callers to this function must disable preemption.
+ */
+static void rcu_qs(void)
+{
+	RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
+	if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) {
+		trace_rcu_grace_period(TPS("rcu_preempt"),
+				       __this_cpu_read(rcu_data.gp_seq),
+				       TPS("cpuqs"));
+		__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
+		barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
+		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
+	}
+}
+
+/*
+ * We have entered the scheduler, and the current task might soon be
+ * context-switched away from.  If this task is in an RCU read-side
+ * critical section, we will no longer be able to rely on the CPU to
+ * record that fact, so we enqueue the task on the blkd_tasks list.
+ * The task will dequeue itself when it exits the outermost enclosing
+ * RCU read-side critical section.  Therefore, the current grace period
+ * cannot be permitted to complete until the blkd_tasks list entries
+ * predating the current grace period drain, in other words, until
+ * rnp->gp_tasks becomes NULL.
+ *
+ * Caller must disable interrupts.
+ */
+void rcu_note_context_switch(bool preempt)
+{
+	struct task_struct *t = current;
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+	struct rcu_node *rnp;
+
+	trace_rcu_utilization(TPS("Start context switch"));
+	lockdep_assert_irqs_disabled();
+	WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!");
+	if (rcu_preempt_depth() > 0 &&
+	    !t->rcu_read_unlock_special.b.blocked) {
+
+		/* Possibly blocking in an RCU read-side critical section. */
+		rnp = rdp->mynode;
+		raw_spin_lock_rcu_node(rnp);
+		t->rcu_read_unlock_special.b.blocked = true;
+		t->rcu_blocked_node = rnp;
+
+		/*
+		 * Verify the CPU's sanity, trace the preemption, and
+		 * then queue the task as required based on the states
+		 * of any ongoing and expedited grace periods.
+		 */
+		WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp));
+		WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
+		trace_rcu_preempt_task(rcu_state.name,
+				       t->pid,
+				       (rnp->qsmask & rdp->grpmask)
+				       ? rnp->gp_seq
+				       : rcu_seq_snap(&rnp->gp_seq));
+		rcu_preempt_ctxt_queue(rnp, rdp);
+	} else {
+		rcu_preempt_deferred_qs(t);
+	}
+
+	/*
+	 * Either we were not in an RCU read-side critical section to
+	 * begin with, or we have now recorded that critical section
+	 * globally.  Either way, we can now note a quiescent state
+	 * for this CPU.  Again, if we were in an RCU read-side critical
+	 * section, and if that critical section was blocking the current
+	 * grace period, then the fact that the task has been enqueued
+	 * means that we continue to block the current grace period.
+	 */
+	rcu_qs();
+	if (rdp->cpu_no_qs.b.exp)
+		rcu_report_exp_rdp(rdp);
+	rcu_tasks_qs(current, preempt);
+	trace_rcu_utilization(TPS("End context switch"));
+}
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
+
+/*
+ * Check for preempted RCU readers blocking the current grace period
+ * for the specified rcu_node structure.  If the caller needs a reliable
+ * answer, it must hold the rcu_node's ->lock.
+ */
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
+{
+	return READ_ONCE(rnp->gp_tasks) != NULL;
+}
+
+/* limit value for ->rcu_read_lock_nesting. */
+#define RCU_NEST_PMAX (INT_MAX / 2)
+
+static void rcu_preempt_read_enter(void)
+{
+	WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1);
+}
+
+static int rcu_preempt_read_exit(void)
+{
+	int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1;
+
+	WRITE_ONCE(current->rcu_read_lock_nesting, ret);
+	return ret;
+}
+
+static void rcu_preempt_depth_set(int val)
+{
+	WRITE_ONCE(current->rcu_read_lock_nesting, val);
+}
+
+/*
+ * Preemptible RCU implementation for rcu_read_lock().
+ * Just increment ->rcu_read_lock_nesting, shared state will be updated
+ * if we block.
+ */
+void __rcu_read_lock(void)
+{
+	rcu_preempt_read_enter();
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING))
+		WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
+	if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread)
+		WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true);
+	barrier();  /* critical section after entry code. */
+}
+EXPORT_SYMBOL_GPL(__rcu_read_lock);
+
+/*
+ * Preemptible RCU implementation for rcu_read_unlock().
+ * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
+ * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
+ * invoke rcu_read_unlock_special() to clean up after a context switch
+ * in an RCU read-side critical section and other special cases.
+ */
+void __rcu_read_unlock(void)
+{
+	struct task_struct *t = current;
+
+	barrier();  // critical section before exit code.
+	if (rcu_preempt_read_exit() == 0) {
+		barrier();  // critical-section exit before .s check.
+		if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
+			rcu_read_unlock_special(t);
+	}
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
+		int rrln = rcu_preempt_depth();
+
+		WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX);
+	}
+}
+EXPORT_SYMBOL_GPL(__rcu_read_unlock);
+
+/*
+ * Advance a ->blkd_tasks-list pointer to the next entry, instead
+ * returning NULL if at the end of the list.
+ */
+static struct list_head *rcu_next_node_entry(struct task_struct *t,
+					     struct rcu_node *rnp)
+{
+	struct list_head *np;
+
+	np = t->rcu_node_entry.next;
+	if (np == &rnp->blkd_tasks)
+		np = NULL;
+	return np;
+}
+
+/*
+ * Return true if the specified rcu_node structure has tasks that were
+ * preempted within an RCU read-side critical section.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
+{
+	return !list_empty(&rnp->blkd_tasks);
+}
+
+/*
+ * Report deferred quiescent states.  The deferral time can
+ * be quite short, for example, in the case of the call from
+ * rcu_read_unlock_special().
+ */
+static notrace void
+rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
+{
+	bool empty_exp;
+	bool empty_norm;
+	bool empty_exp_now;
+	struct list_head *np;
+	bool drop_boost_mutex = false;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	union rcu_special special;
+
+	/*
+	 * If RCU core is waiting for this CPU to exit its critical section,
+	 * report the fact that it has exited.  Because irqs are disabled,
+	 * t->rcu_read_unlock_special cannot change.
+	 */
+	special = t->rcu_read_unlock_special;
+	rdp = this_cpu_ptr(&rcu_data);
+	if (!special.s && !rdp->cpu_no_qs.b.exp) {
+		local_irq_restore(flags);
+		return;
+	}
+	t->rcu_read_unlock_special.s = 0;
+	if (special.b.need_qs) {
+		if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
+			rdp->cpu_no_qs.b.norm = false;
+			rcu_report_qs_rdp(rdp);
+			udelay(rcu_unlock_delay);
+		} else {
+			rcu_qs();
+		}
+	}
+
+	/*
+	 * Respond to a request by an expedited grace period for a
+	 * quiescent state from this CPU.  Note that requests from
+	 * tasks are handled when removing the task from the
+	 * blocked-tasks list below.
+	 */
+	if (rdp->cpu_no_qs.b.exp)
+		rcu_report_exp_rdp(rdp);
+
+	/* Clean up if blocked during RCU read-side critical section. */
+	if (special.b.blocked) {
+
+		/*
+		 * Remove this task from the list it blocked on.  The task
+		 * now remains queued on the rcu_node corresponding to the
+		 * CPU it first blocked on, so there is no longer any need
+		 * to loop.  Retain a WARN_ON_ONCE() out of sheer paranoia.
+		 */
+		rnp = t->rcu_blocked_node;
+		raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
+		WARN_ON_ONCE(rnp != t->rcu_blocked_node);
+		WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
+		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
+		WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
+			     (!empty_norm || rnp->qsmask));
+		empty_exp = sync_rcu_exp_done(rnp);
+		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
+		np = rcu_next_node_entry(t, rnp);
+		list_del_init(&t->rcu_node_entry);
+		t->rcu_blocked_node = NULL;
+		trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
+						rnp->gp_seq, t->pid);
+		if (&t->rcu_node_entry == rnp->gp_tasks)
+			WRITE_ONCE(rnp->gp_tasks, np);
+		if (&t->rcu_node_entry == rnp->exp_tasks)
+			WRITE_ONCE(rnp->exp_tasks, np);
+		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
+			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
+			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t;
+			if (&t->rcu_node_entry == rnp->boost_tasks)
+				WRITE_ONCE(rnp->boost_tasks, np);
+		}
+
+		/*
+		 * If this was the last task on the current list, and if
+		 * we aren't waiting on any CPUs, report the quiescent state.
+		 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
+		 * so we must take a snapshot of the expedited state.
+		 */
+		empty_exp_now = sync_rcu_exp_done(rnp);
+		if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
+			trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
+							 rnp->gp_seq,
+							 0, rnp->qsmask,
+							 rnp->level,
+							 rnp->grplo,
+							 rnp->grphi,
+							 !!rnp->gp_tasks);
+			rcu_report_unblock_qs_rnp(rnp, flags);
+		} else {
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		}
+
+		/*
+		 * If this was the last task on the expedited lists,
+		 * then we need to report up the rcu_node hierarchy.
+		 */
+		if (!empty_exp && empty_exp_now)
+			rcu_report_exp_rnp(rnp, true);
+
+		/* Unboost if we were boosted. */
+		if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
+			rt_mutex_futex_unlock(&rnp->boost_mtx.rtmutex);
+	} else {
+		local_irq_restore(flags);
+	}
+}
+
+/*
+ * Is a deferred quiescent-state pending, and are we also not in
+ * an RCU read-side critical section?  It is the caller's responsibility
+ * to ensure it is otherwise safe to report any deferred quiescent
+ * states.  The reason for this is that it is safe to report a
+ * quiescent state during context switch even though preemption
+ * is disabled.  This function cannot be expected to understand these
+ * nuances, so the caller must handle them.
+ */
+static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
+{
+	return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) ||
+		READ_ONCE(t->rcu_read_unlock_special.s)) &&
+	       rcu_preempt_depth() == 0;
+}
+
+/*
+ * Report a deferred quiescent state if needed and safe to do so.
+ * As with rcu_preempt_need_deferred_qs(), "safe" involves only
+ * not being in an RCU read-side critical section.  The caller must
+ * evaluate safety in terms of interrupt, softirq, and preemption
+ * disabling.
+ */
+notrace void rcu_preempt_deferred_qs(struct task_struct *t)
+{
+	unsigned long flags;
+
+	if (!rcu_preempt_need_deferred_qs(t))
+		return;
+	local_irq_save(flags);
+	rcu_preempt_deferred_qs_irqrestore(t, flags);
+}
+
+/*
+ * Minimal handler to give the scheduler a chance to re-evaluate.
+ */
+static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
+{
+	struct rcu_data *rdp;
+
+	rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
+	rdp->defer_qs_iw_pending = false;
+}
+
+/*
+ * Handle special cases during rcu_read_unlock(), such as needing to
+ * notify RCU core processing or task having blocked during the RCU
+ * read-side critical section.
+ */
+static void rcu_read_unlock_special(struct task_struct *t)
+{
+	unsigned long flags;
+	bool irqs_were_disabled;
+	bool preempt_bh_were_disabled =
+			!!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
+
+	/* NMI handlers cannot block and cannot safely manipulate state. */
+	if (in_nmi())
+		return;
+
+	local_irq_save(flags);
+	irqs_were_disabled = irqs_disabled_flags(flags);
+	if (preempt_bh_were_disabled || irqs_were_disabled) {
+		bool expboost; // Expedited GP in flight or possible boosting.
+		struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+		struct rcu_node *rnp = rdp->mynode;
+
+		expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
+			   (rdp->grpmask & READ_ONCE(rnp->expmask)) ||
+			   (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
+			   ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) ||
+			   (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled &&
+			    t->rcu_blocked_node);
+		// Need to defer quiescent state until everything is enabled.
+		if (use_softirq && (in_hardirq() || (expboost && !irqs_were_disabled))) {
+			// Using softirq, safe to awaken, and either the
+			// wakeup is free or there is either an expedited
+			// GP in flight or a potential need to deboost.
+			raise_softirq_irqoff(RCU_SOFTIRQ);
+		} else {
+			// Enabling BH or preempt does reschedule, so...
+			// Also if no expediting and no possible deboosting,
+			// slow is OK.  Plus nohz_full CPUs eventually get
+			// tick enabled.
+			set_tsk_need_resched(current);
+			set_preempt_need_resched();
+			if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
+			    expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
+				// Get scheduler to re-evaluate and call hooks.
+				// If !IRQ_WORK, FQS scan will eventually IPI.
+				if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
+				    IS_ENABLED(CONFIG_PREEMPT_RT))
+					rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
+								rcu_preempt_deferred_qs_handler);
+				else
+					init_irq_work(&rdp->defer_qs_iw,
+						      rcu_preempt_deferred_qs_handler);
+				rdp->defer_qs_iw_pending = true;
+				irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
+			}
+		}
+		local_irq_restore(flags);
+		return;
+	}
+	rcu_preempt_deferred_qs_irqrestore(t, flags);
+}
+
+/*
+ * Check that the list of blocked tasks for the newly completed grace
+ * period is in fact empty.  It is a serious bug to complete a grace
+ * period that still has RCU readers blocked!  This function must be
+ * invoked -before- updating this rnp's ->gp_seq.
+ *
+ * Also, if there are blocked tasks on the list, they automatically
+ * block the newly created grace period, so set up ->gp_tasks accordingly.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+	struct task_struct *t;
+
+	RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
+	raw_lockdep_assert_held_rcu_node(rnp);
+	if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
+		dump_blkd_tasks(rnp, 10);
+	if (rcu_preempt_has_tasks(rnp) &&
+	    (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
+		WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
+		t = container_of(rnp->gp_tasks, struct task_struct,
+				 rcu_node_entry);
+		trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
+						rnp->gp_seq, t->pid);
+	}
+	WARN_ON_ONCE(rnp->qsmask);
+}
+
+/*
+ * Check for a quiescent state from the current CPU, including voluntary
+ * context switches for Tasks RCU.  When a task blocks, the task is
+ * recorded in the corresponding CPU's rcu_node structure, which is checked
+ * elsewhere, hence this function need only check for quiescent states
+ * related to the current CPU, not to those related to tasks.
+ */
+static void rcu_flavor_sched_clock_irq(int user)
+{
+	struct task_struct *t = current;
+
+	lockdep_assert_irqs_disabled();
+	if (rcu_preempt_depth() > 0 ||
+	    (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
+		/* No QS, force context switch if deferred. */
+		if (rcu_preempt_need_deferred_qs(t)) {
+			set_tsk_need_resched(t);
+			set_preempt_need_resched();
+		}
+	} else if (rcu_preempt_need_deferred_qs(t)) {
+		rcu_preempt_deferred_qs(t); /* Report deferred QS. */
+		return;
+	} else if (!WARN_ON_ONCE(rcu_preempt_depth())) {
+		rcu_qs(); /* Report immediate QS. */
+		return;
+	}
+
+	/* If GP is oldish, ask for help from rcu_read_unlock_special(). */
+	if (rcu_preempt_depth() > 0 &&
+	    __this_cpu_read(rcu_data.core_needs_qs) &&
+	    __this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
+	    !t->rcu_read_unlock_special.b.need_qs &&
+	    time_after(jiffies, rcu_state.gp_start + HZ))
+		t->rcu_read_unlock_special.b.need_qs = true;
+}
+
+/*
+ * Check for a task exiting while in a preemptible-RCU read-side
+ * critical section, clean up if so.  No need to issue warnings, as
+ * debug_check_no_locks_held() already does this if lockdep is enabled.
+ * Besides, if this function does anything other than just immediately
+ * return, there was a bug of some sort.  Spewing warnings from this
+ * function is like as not to simply obscure important prior warnings.
+ */
+void exit_rcu(void)
+{
+	struct task_struct *t = current;
+
+	if (unlikely(!list_empty(&current->rcu_node_entry))) {
+		rcu_preempt_depth_set(1);
+		barrier();
+		WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
+	} else if (unlikely(rcu_preempt_depth())) {
+		rcu_preempt_depth_set(1);
+	} else {
+		return;
+	}
+	__rcu_read_unlock();
+	rcu_preempt_deferred_qs(current);
+}
+
+/*
+ * Dump the blocked-tasks state, but limit the list dump to the
+ * specified number of elements.
+ */
+static void
+dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
+{
+	int cpu;
+	int i;
+	struct list_head *lhp;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp1;
+
+	raw_lockdep_assert_held_rcu_node(rnp);
+	pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
+		__func__, rnp->grplo, rnp->grphi, rnp->level,
+		(long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs);
+	for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
+		pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
+			__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
+	pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
+		__func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
+		READ_ONCE(rnp->exp_tasks));
+	pr_info("%s: ->blkd_tasks", __func__);
+	i = 0;
+	list_for_each(lhp, &rnp->blkd_tasks) {
+		pr_cont(" %p", lhp);
+		if (++i >= ncheck)
+			break;
+	}
+	pr_cont("\n");
+	for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
+		rdp = per_cpu_ptr(&rcu_data, cpu);
+		pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
+			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);
+	}
+}
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/*
+ * If strict grace periods are enabled, and if the calling
+ * __rcu_read_unlock() marks the beginning of a quiescent state, immediately
+ * report that quiescent state and, if requested, spin for a bit.
+ */
+void rcu_read_unlock_strict(void)
+{
+	struct rcu_data *rdp;
+
+	if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
+		return;
+	rdp = this_cpu_ptr(&rcu_data);
+	rdp->cpu_no_qs.b.norm = false;
+	rcu_report_qs_rdp(rdp);
+	udelay(rcu_unlock_delay);
+}
+EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
+
+/*
+ * Tell them what RCU they are running.
+ */
+static void __init rcu_bootup_announce(void)
+{
+	pr_info("Hierarchical RCU implementation.\n");
+	rcu_bootup_announce_oddness();
+}
+
+/*
+ * Note a quiescent state for PREEMPTION=n.  Because we do not need to know
+ * how many quiescent states passed, just if there was at least one since
+ * the start of the grace period, this just sets a flag.  The caller must
+ * have disabled preemption.
+ */
+static void rcu_qs(void)
+{
+	RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
+	if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
+		return;
+	trace_rcu_grace_period(TPS("rcu_sched"),
+			       __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
+	__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
+	if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
+		rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
+}
+
+/*
+ * Register an urgently needed quiescent state.  If there is an
+ * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
+ * dyntick-idle quiescent state visible to other CPUs, which will in
+ * some cases serve for expedited as well as normal grace periods.
+ * Either way, register a lightweight quiescent state.
+ */
+void rcu_all_qs(void)
+{
+	unsigned long flags;
+
+	if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
+		return;
+	preempt_disable();  // For CONFIG_PREEMPT_COUNT=y kernels
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
+		preempt_enable();
+		return;
+	}
+	this_cpu_write(rcu_data.rcu_urgent_qs, false);
+	if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
+		local_irq_save(flags);
+		rcu_momentary_dyntick_idle();
+		local_irq_restore(flags);
+	}
+	rcu_qs();
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(rcu_all_qs);
+
+/*
+ * Note a PREEMPTION=n context switch. The caller must have disabled interrupts.
+ */
+void rcu_note_context_switch(bool preempt)
+{
+	trace_rcu_utilization(TPS("Start context switch"));
+	rcu_qs();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
+		goto out;
+	this_cpu_write(rcu_data.rcu_urgent_qs, false);
+	if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
+		rcu_momentary_dyntick_idle();
+out:
+	rcu_tasks_qs(current, preempt);
+	trace_rcu_utilization(TPS("End context switch"));
+}
+EXPORT_SYMBOL_GPL(rcu_note_context_switch);
+
+/*
+ * Because preemptible RCU does not exist, there are never any preempted
+ * RCU readers.
+ */
+static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
+{
+	return 0;
+}
+
+/*
+ * Because there is no preemptible RCU, there can be no readers blocked.
+ */
+static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
+{
+	return false;
+}
+
+/*
+ * Because there is no preemptible RCU, there can be no deferred quiescent
+ * states.
+ */
+static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
+{
+	return false;
+}
+
+// Except that we do need to respond to a request by an expedited
+// grace period for a quiescent state from this CPU.  Note that in
+// non-preemptible kernels, there can be no context switches within RCU
+// read-side critical sections, which in turn means that the leaf rcu_node
+// structure's blocked-tasks list is always empty.  is therefore no need to
+// actually check it.  Instead, a quiescent state from this CPU suffices,
+// and this function is only called from such a quiescent state.
+notrace void rcu_preempt_deferred_qs(struct task_struct *t)
+{
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+
+	if (READ_ONCE(rdp->cpu_no_qs.b.exp))
+		rcu_report_exp_rdp(rdp);
+}
+
+/*
+ * Because there is no preemptible RCU, there can be no readers blocked,
+ * so there is no need to check for blocked tasks.  So check only for
+ * bogus qsmask values.
+ */
+static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
+{
+	WARN_ON_ONCE(rnp->qsmask);
+}
+
+/*
+ * Check to see if this CPU is in a non-context-switch quiescent state,
+ * namely user mode and idle loop.
+ */
+static void rcu_flavor_sched_clock_irq(int user)
+{
+	if (user || rcu_is_cpu_rrupt_from_idle()) {
+
+		/*
+		 * Get here if this CPU took its interrupt from user
+		 * mode or from the idle loop, and if this is not a
+		 * nested interrupt.  In this case, the CPU is in
+		 * a quiescent state, so note it.
+		 *
+		 * No memory barrier is required here because rcu_qs()
+		 * references only CPU-local variables that other CPUs
+		 * neither access nor modify, at least not while the
+		 * corresponding CPU is online.
+		 */
+		rcu_qs();
+	}
+}
+
+/*
+ * Because preemptible RCU does not exist, tasks cannot possibly exit
+ * while in preemptible RCU read-side critical sections.
+ */
+void exit_rcu(void)
+{
+}
+
+/*
+ * Dump the guaranteed-empty blocked-tasks state.  Trust but verify.
+ */
+static void
+dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
+{
+	WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
+}
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+/*
+ * If boosting, set rcuc kthreads to realtime priority.
+ */
+static void rcu_cpu_kthread_setup(unsigned int cpu)
+{
+	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+#ifdef CONFIG_RCU_BOOST
+	struct sched_param sp;
+
+	sp.sched_priority = kthread_prio;
+	sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+#endif /* #ifdef CONFIG_RCU_BOOST */
+
+	WRITE_ONCE(rdp->rcuc_activity, jiffies);
+}
+
+static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp)
+{
+#ifdef CONFIG_RCU_NOCB_CPU
+	return rdp->nocb_cb_kthread == current;
+#else
+	return false;
+#endif
+}
+
+/*
+ * Is the current CPU running the RCU-callbacks kthread?
+ * Caller must have preemption disabled.
+ */
+static bool rcu_is_callbacks_kthread(struct rcu_data *rdp)
+{
+	return rdp->rcu_cpu_kthread_task == current ||
+			rcu_is_callbacks_nocb_kthread(rdp);
+}
+
+#ifdef CONFIG_RCU_BOOST
+
+/*
+ * Carry out RCU priority boosting on the task indicated by ->exp_tasks
+ * or ->boost_tasks, advancing the pointer to the next task in the
+ * ->blkd_tasks list.
+ *
+ * Note that irqs must be enabled: boosting the task can block.
+ * Returns 1 if there are more tasks needing to be boosted.
+ */
+static int rcu_boost(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	struct task_struct *t;
+	struct list_head *tb;
+
+	if (READ_ONCE(rnp->exp_tasks) == NULL &&
+	    READ_ONCE(rnp->boost_tasks) == NULL)
+		return 0;  /* Nothing left to boost. */
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+
+	/*
+	 * Recheck under the lock: all tasks in need of boosting
+	 * might exit their RCU read-side critical sections on their own.
+	 */
+	if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return 0;
+	}
+
+	/*
+	 * Preferentially boost tasks blocking expedited grace periods.
+	 * This cannot starve the normal grace periods because a second
+	 * expedited grace period must boost all blocked tasks, including
+	 * those blocking the pre-existing normal grace period.
+	 */
+	if (rnp->exp_tasks != NULL)
+		tb = rnp->exp_tasks;
+	else
+		tb = rnp->boost_tasks;
+
+	/*
+	 * We boost task t by manufacturing an rt_mutex that appears to
+	 * be held by task t.  We leave a pointer to that rt_mutex where
+	 * task t can find it, and task t will release the mutex when it
+	 * exits its outermost RCU read-side critical section.  Then
+	 * simply acquiring this artificial rt_mutex will boost task
+	 * t's priority.  (Thanks to tglx for suggesting this approach!)
+	 *
+	 * Note that task t must acquire rnp->lock to remove itself from
+	 * the ->blkd_tasks list, which it will do from exit() if from
+	 * nowhere else.  We therefore are guaranteed that task t will
+	 * stay around at least until we drop rnp->lock.  Note that
+	 * rnp->lock also resolves races between our priority boosting
+	 * and task t's exiting its outermost RCU read-side critical
+	 * section.
+	 */
+	t = container_of(tb, struct task_struct, rcu_node_entry);
+	rt_mutex_init_proxy_locked(&rnp->boost_mtx.rtmutex, t);
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	/* Lock only for side effect: boosts task t's priority. */
+	rt_mutex_lock(&rnp->boost_mtx);
+	rt_mutex_unlock(&rnp->boost_mtx);  /* Then keep lockdep happy. */
+	rnp->n_boosts++;
+
+	return READ_ONCE(rnp->exp_tasks) != NULL ||
+	       READ_ONCE(rnp->boost_tasks) != NULL;
+}
+
+/*
+ * Priority-boosting kthread, one per leaf rcu_node.
+ */
+static int rcu_boost_kthread(void *arg)
+{
+	struct rcu_node *rnp = (struct rcu_node *)arg;
+	int spincnt = 0;
+	int more2boost;
+
+	trace_rcu_utilization(TPS("Start boost kthread@init"));
+	for (;;) {
+		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
+		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
+		rcu_wait(READ_ONCE(rnp->boost_tasks) ||
+			 READ_ONCE(rnp->exp_tasks));
+		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
+		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
+		more2boost = rcu_boost(rnp);
+		if (more2boost)
+			spincnt++;
+		else
+			spincnt = 0;
+		if (spincnt > 10) {
+			WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
+			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
+			schedule_timeout_idle(2);
+			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
+			spincnt = 0;
+		}
+	}
+	/* NOTREACHED */
+	trace_rcu_utilization(TPS("End boost kthread@notreached"));
+	return 0;
+}
+
+/*
+ * Check to see if it is time to start boosting RCU readers that are
+ * blocking the current grace period, and, if so, tell the per-rcu_node
+ * kthread to start boosting them.  If there is an expedited grace
+ * period in progress, it is always time to boost.
+ *
+ * The caller must hold rnp->lock, which this function releases.
+ * The ->boost_kthread_task is immortal, so we don't need to worry
+ * about it going away.
+ */
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+	__releases(rnp->lock)
+{
+	raw_lockdep_assert_held_rcu_node(rnp);
+	if (!rnp->boost_kthread_task ||
+	    (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	if (rnp->exp_tasks != NULL ||
+	    (rnp->gp_tasks != NULL &&
+	     rnp->boost_tasks == NULL &&
+	     rnp->qsmask == 0 &&
+	     (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld ||
+	      IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) {
+		if (rnp->exp_tasks == NULL)
+			WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		rcu_wake_cond(rnp->boost_kthread_task,
+			      READ_ONCE(rnp->boost_kthread_status));
+	} else {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+}
+
+#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
+
+/*
+ * Do priority-boost accounting for the start of a new grace period.
+ */
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+	rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
+}
+
+/*
+ * Create an RCU-boost kthread for the specified node if one does not
+ * already exist.  We only create this kthread for preemptible RCU.
+ */
+static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	int rnp_index = rnp - rcu_get_root();
+	struct sched_param sp;
+	struct task_struct *t;
+
+	mutex_lock(&rnp->boost_kthread_mutex);
+	if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
+		goto out;
+
+	t = kthread_create(rcu_boost_kthread, (void *)rnp,
+			   "rcub/%d", rnp_index);
+	if (WARN_ON_ONCE(IS_ERR(t)))
+		goto out;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	rnp->boost_kthread_task = t;
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	sp.sched_priority = kthread_prio;
+	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
+
+ out:
+	mutex_unlock(&rnp->boost_kthread_mutex);
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question.  The CPU hotplug lock is still
+ * held, so the value of rnp->qsmaskinit will be stable.
+ *
+ * We don't include outgoingcpu in the affinity set, use -1 if there is
+ * no outgoing CPU.  If there are no CPUs left in the affinity set,
+ * this function allows the kthread to execute on any CPU.
+ */
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+	struct task_struct *t = rnp->boost_kthread_task;
+	unsigned long mask = rcu_rnp_online_cpus(rnp);
+	cpumask_var_t cm;
+	int cpu;
+
+	if (!t)
+		return;
+	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
+		return;
+	mutex_lock(&rnp->boost_kthread_mutex);
+	for_each_leaf_node_possible_cpu(rnp, cpu)
+		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
+		    cpu != outgoingcpu)
+			cpumask_set_cpu(cpu, cm);
+	cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
+	if (cpumask_empty(cm)) {
+		cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
+		if (outgoingcpu >= 0)
+			cpumask_clear_cpu(outgoingcpu, cm);
+	}
+	set_cpus_allowed_ptr(t, cm);
+	mutex_unlock(&rnp->boost_kthread_mutex);
+	free_cpumask_var(cm);
+}
+
+#else /* #ifdef CONFIG_RCU_BOOST */
+
+static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
+	__releases(rnp->lock)
+{
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+}
+
+static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
+{
+}
+
+static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
+{
+}
+
+static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
+{
+}
+
+#endif /* #else #ifdef CONFIG_RCU_BOOST */
+
+/*
+ * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
+ * grace-period kthread will do force_quiescent_state() processing?
+ * The idea is to avoid waking up RCU core processing on such a
+ * CPU unless the grace period has extended for too long.
+ *
+ * This code relies on the fact that all NO_HZ_FULL CPUs are also
+ * RCU_NOCB_CPU CPUs.
+ */
+static bool rcu_nohz_full_cpu(void)
+{
+#ifdef CONFIG_NO_HZ_FULL
+	if (tick_nohz_full_cpu(smp_processor_id()) &&
+	    (!rcu_gp_in_progress() ||
+	     time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
+		return true;
+#endif /* #ifdef CONFIG_NO_HZ_FULL */
+	return false;
+}
+
+/*
+ * Bind the RCU grace-period kthreads to the housekeeping CPU.
+ */
+static void rcu_bind_gp_kthread(void)
+{
+	if (!tick_nohz_full_enabled())
+		return;
+	housekeeping_affine(current, HK_TYPE_RCU);
+}