Adding upstream version 6.1.76.upstream/6.1.76

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

1 files changed, 1109 insertions, 0 deletions

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
new file mode 100644
index 000000000..6d2cbed96
--- /dev/null
+++ b/kernel/rcu/tree_exp.h
@@ -0,0 +1,1109 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * RCU expedited grace periods
+ *
+ * Copyright IBM Corporation, 2016
+ *
+ * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
+ */
+
+#include <linux/lockdep.h>
+
+static void rcu_exp_handler(void *unused);
+static int rcu_print_task_exp_stall(struct rcu_node *rnp);
+
+/*
+ * Record the start of an expedited grace period.
+ */
+static void rcu_exp_gp_seq_start(void)
+{
+	rcu_seq_start(&rcu_state.expedited_sequence);
+	rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
+}
+
+/*
+ * Return the value that the expedited-grace-period counter will have
+ * at the end of the current grace period.
+ */
+static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
+{
+	return rcu_seq_endval(&rcu_state.expedited_sequence);
+}
+
+/*
+ * Record the end of an expedited grace period.
+ */
+static void rcu_exp_gp_seq_end(void)
+{
+	rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
+	rcu_seq_end(&rcu_state.expedited_sequence);
+	smp_mb(); /* Ensure that consecutive grace periods serialize. */
+}
+
+/*
+ * Take a snapshot of the expedited-grace-period counter, which is the
+ * earliest value that will indicate that a full grace period has
+ * elapsed since the current time.
+ */
+static unsigned long rcu_exp_gp_seq_snap(void)
+{
+	unsigned long s;
+
+	smp_mb(); /* Caller's modifications seen first by other CPUs. */
+	s = rcu_seq_snap(&rcu_state.expedited_sequence);
+	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
+	return s;
+}
+
+/*
+ * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
+ * if a full expedited grace period has elapsed since that snapshot
+ * was taken.
+ */
+static bool rcu_exp_gp_seq_done(unsigned long s)
+{
+	return rcu_seq_done(&rcu_state.expedited_sequence, s);
+}
+
+/*
+ * Reset the ->expmaskinit values in the rcu_node tree to reflect any
+ * recent CPU-online activity.  Note that these masks are not cleared
+ * when CPUs go offline, so they reflect the union of all CPUs that have
+ * ever been online.  This means that this function normally takes its
+ * no-work-to-do fastpath.
+ */
+static void sync_exp_reset_tree_hotplug(void)
+{
+	bool done;
+	unsigned long flags;
+	unsigned long mask;
+	unsigned long oldmask;
+	int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
+	struct rcu_node *rnp;
+	struct rcu_node *rnp_up;
+
+	/* If no new CPUs onlined since last time, nothing to do. */
+	if (likely(ncpus == rcu_state.ncpus_snap))
+		return;
+	rcu_state.ncpus_snap = ncpus;
+
+	/*
+	 * Each pass through the following loop propagates newly onlined
+	 * CPUs for the current rcu_node structure up the rcu_node tree.
+	 */
+	rcu_for_each_leaf_node(rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		if (rnp->expmaskinit == rnp->expmaskinitnext) {
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			continue;  /* No new CPUs, nothing to do. */
+		}
+
+		/* Update this node's mask, track old value for propagation. */
+		oldmask = rnp->expmaskinit;
+		rnp->expmaskinit = rnp->expmaskinitnext;
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+		/* If was already nonzero, nothing to propagate. */
+		if (oldmask)
+			continue;
+
+		/* Propagate the new CPU up the tree. */
+		mask = rnp->grpmask;
+		rnp_up = rnp->parent;
+		done = false;
+		while (rnp_up) {
+			raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
+			if (rnp_up->expmaskinit)
+				done = true;
+			rnp_up->expmaskinit |= mask;
+			raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
+			if (done)
+				break;
+			mask = rnp_up->grpmask;
+			rnp_up = rnp_up->parent;
+		}
+	}
+}
+
+/*
+ * Reset the ->expmask values in the rcu_node tree in preparation for
+ * a new expedited grace period.
+ */
+static void __maybe_unused sync_exp_reset_tree(void)
+{
+	unsigned long flags;
+	struct rcu_node *rnp;
+
+	sync_exp_reset_tree_hotplug();
+	rcu_for_each_node_breadth_first(rnp) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		WARN_ON_ONCE(rnp->expmask);
+		WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+}
+
+/*
+ * Return non-zero if there is no RCU expedited grace period in progress
+ * for the specified rcu_node structure, in other words, if all CPUs and
+ * tasks covered by the specified rcu_node structure have done their bit
+ * for the current expedited grace period.
+ */
+static bool sync_rcu_exp_done(struct rcu_node *rnp)
+{
+	raw_lockdep_assert_held_rcu_node(rnp);
+	return READ_ONCE(rnp->exp_tasks) == NULL &&
+	       READ_ONCE(rnp->expmask) == 0;
+}
+
+/*
+ * Like sync_rcu_exp_done(), but where the caller does not hold the
+ * rcu_node's ->lock.
+ */
+static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	bool ret;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	ret = sync_rcu_exp_done(rnp);
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+	return ret;
+}
+
+/*
+ * Report the exit from RCU read-side critical section for the last task
+ * that queued itself during or before the current expedited preemptible-RCU
+ * grace period.  This event is reported either to the rcu_node structure on
+ * which the task was queued or to one of that rcu_node structure's ancestors,
+ * recursively up the tree.  (Calm down, calm down, we do the recursion
+ * iteratively!)
+ */
+static void __rcu_report_exp_rnp(struct rcu_node *rnp,
+				 bool wake, unsigned long flags)
+	__releases(rnp->lock)
+{
+	unsigned long mask;
+
+	raw_lockdep_assert_held_rcu_node(rnp);
+	for (;;) {
+		if (!sync_rcu_exp_done(rnp)) {
+			if (!rnp->expmask)
+				rcu_initiate_boost(rnp, flags);
+			else
+				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			break;
+		}
+		if (rnp->parent == NULL) {
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			if (wake) {
+				smp_mb(); /* EGP done before wake_up(). */
+				swake_up_one_online(&rcu_state.expedited_wq);
+			}
+			break;
+		}
+		mask = rnp->grpmask;
+		raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
+		rnp = rnp->parent;
+		raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
+		WARN_ON_ONCE(!(rnp->expmask & mask));
+		WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
+	}
+}
+
+/*
+ * Report expedited quiescent state for specified node.  This is a
+ * lock-acquisition wrapper function for __rcu_report_exp_rnp().
+ */
+static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	__rcu_report_exp_rnp(rnp, wake, flags);
+}
+
+/*
+ * Report expedited quiescent state for multiple CPUs, all covered by the
+ * specified leaf rcu_node structure.
+ */
+static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
+				    unsigned long mask, bool wake)
+{
+	int cpu;
+	unsigned long flags;
+	struct rcu_data *rdp;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	if (!(rnp->expmask & mask)) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+	WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
+	for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
+		rdp = per_cpu_ptr(&rcu_data, cpu);
+		if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
+			continue;
+		rdp->rcu_forced_tick_exp = false;
+		tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
+	}
+	__rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
+}
+
+/*
+ * Report expedited quiescent state for specified rcu_data (CPU).
+ */
+static void rcu_report_exp_rdp(struct rcu_data *rdp)
+{
+	WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
+	rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
+}
+
+/* Common code for work-done checking. */
+static bool sync_exp_work_done(unsigned long s)
+{
+	if (rcu_exp_gp_seq_done(s)) {
+		trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
+		smp_mb(); /* Ensure test happens before caller kfree(). */
+		return true;
+	}
+	return false;
+}
+
+/*
+ * Funnel-lock acquisition for expedited grace periods.  Returns true
+ * if some other task completed an expedited grace period that this task
+ * can piggy-back on, and with no mutex held.  Otherwise, returns false
+ * with the mutex held, indicating that the caller must actually do the
+ * expedited grace period.
+ */
+static bool exp_funnel_lock(unsigned long s)
+{
+	struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
+	struct rcu_node *rnp = rdp->mynode;
+	struct rcu_node *rnp_root = rcu_get_root();
+
+	/* Low-contention fastpath. */
+	if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
+	    (rnp == rnp_root ||
+	     ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
+	    mutex_trylock(&rcu_state.exp_mutex))
+		goto fastpath;
+
+	/*
+	 * Each pass through the following loop works its way up
+	 * the rcu_node tree, returning if others have done the work or
+	 * otherwise falls through to acquire ->exp_mutex.  The mapping
+	 * from CPU to rcu_node structure can be inexact, as it is just
+	 * promoting locality and is not strictly needed for correctness.
+	 */
+	for (; rnp != NULL; rnp = rnp->parent) {
+		if (sync_exp_work_done(s))
+			return true;
+
+		/* Work not done, either wait here or go up. */
+		spin_lock(&rnp->exp_lock);
+		if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
+
+			/* Someone else doing GP, so wait for them. */
+			spin_unlock(&rnp->exp_lock);
+			trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
+						  rnp->grplo, rnp->grphi,
+						  TPS("wait"));
+			wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
+				   sync_exp_work_done(s));
+			return true;
+		}
+		WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
+		spin_unlock(&rnp->exp_lock);
+		trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
+					  rnp->grplo, rnp->grphi, TPS("nxtlvl"));
+	}
+	mutex_lock(&rcu_state.exp_mutex);
+fastpath:
+	if (sync_exp_work_done(s)) {
+		mutex_unlock(&rcu_state.exp_mutex);
+		return true;
+	}
+	rcu_exp_gp_seq_start();
+	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
+	return false;
+}
+
+/*
+ * Select the CPUs within the specified rcu_node that the upcoming
+ * expedited grace period needs to wait for.
+ */
+static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
+{
+	int cpu;
+	unsigned long flags;
+	unsigned long mask_ofl_test;
+	unsigned long mask_ofl_ipi;
+	int ret;
+	struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+
+	/* Each pass checks a CPU for identity, offline, and idle. */
+	mask_ofl_test = 0;
+	for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
+		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+		unsigned long mask = rdp->grpmask;
+		int snap;
+
+		if (raw_smp_processor_id() == cpu ||
+		    !(rnp->qsmaskinitnext & mask)) {
+			mask_ofl_test |= mask;
+		} else {
+			snap = rcu_dynticks_snap(cpu);
+			if (rcu_dynticks_in_eqs(snap))
+				mask_ofl_test |= mask;
+			else
+				rdp->exp_dynticks_snap = snap;
+		}
+	}
+	mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
+
+	/*
+	 * Need to wait for any blocked tasks as well.	Note that
+	 * additional blocking tasks will also block the expedited GP
+	 * until such time as the ->expmask bits are cleared.
+	 */
+	if (rcu_preempt_has_tasks(rnp))
+		WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next);
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+	/* IPI the remaining CPUs for expedited quiescent state. */
+	for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
+		struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+		unsigned long mask = rdp->grpmask;
+
+retry_ipi:
+		if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
+			mask_ofl_test |= mask;
+			continue;
+		}
+		if (get_cpu() == cpu) {
+			mask_ofl_test |= mask;
+			put_cpu();
+			continue;
+		}
+		ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
+		put_cpu();
+		/* The CPU will report the QS in response to the IPI. */
+		if (!ret)
+			continue;
+
+		/* Failed, raced with CPU hotplug operation. */
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		if ((rnp->qsmaskinitnext & mask) &&
+		    (rnp->expmask & mask)) {
+			/* Online, so delay for a bit and try again. */
+			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+			trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
+			schedule_timeout_idle(1);
+			goto retry_ipi;
+		}
+		/* CPU really is offline, so we must report its QS. */
+		if (rnp->expmask & mask)
+			mask_ofl_test |= mask;
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	}
+	/* Report quiescent states for those that went offline. */
+	if (mask_ofl_test)
+		rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
+}
+
+static void rcu_exp_sel_wait_wake(unsigned long s);
+
+#ifdef CONFIG_RCU_EXP_KTHREAD
+static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
+{
+	struct rcu_exp_work *rewp =
+		container_of(wp, struct rcu_exp_work, rew_work);
+
+	__sync_rcu_exp_select_node_cpus(rewp);
+}
+
+static inline bool rcu_gp_par_worker_started(void)
+{
+	return !!READ_ONCE(rcu_exp_par_gp_kworker);
+}
+
+static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
+{
+	kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
+	/*
+	 * Use rcu_exp_par_gp_kworker, because flushing a work item from
+	 * another work item on the same kthread worker can result in
+	 * deadlock.
+	 */
+	kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
+}
+
+static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
+{
+	kthread_flush_work(&rnp->rew.rew_work);
+}
+
+/*
+ * Work-queue handler to drive an expedited grace period forward.
+ */
+static void wait_rcu_exp_gp(struct kthread_work *wp)
+{
+	struct rcu_exp_work *rewp;
+
+	rewp = container_of(wp, struct rcu_exp_work, rew_work);
+	rcu_exp_sel_wait_wake(rewp->rew_s);
+}
+
+static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
+{
+	kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
+	kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
+}
+
+static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
+{
+}
+#else /* !CONFIG_RCU_EXP_KTHREAD */
+static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
+{
+	struct rcu_exp_work *rewp =
+		container_of(wp, struct rcu_exp_work, rew_work);
+
+	__sync_rcu_exp_select_node_cpus(rewp);
+}
+
+static inline bool rcu_gp_par_worker_started(void)
+{
+	return !!READ_ONCE(rcu_par_gp_wq);
+}
+
+static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
+{
+	int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
+
+	INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
+	/* If all offline, queue the work on an unbound CPU. */
+	if (unlikely(cpu > rnp->grphi - rnp->grplo))
+		cpu = WORK_CPU_UNBOUND;
+	else
+		cpu += rnp->grplo;
+	queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
+}
+
+static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
+{
+	flush_work(&rnp->rew.rew_work);
+}
+
+/*
+ * Work-queue handler to drive an expedited grace period forward.
+ */
+static void wait_rcu_exp_gp(struct work_struct *wp)
+{
+	struct rcu_exp_work *rewp;
+
+	rewp = container_of(wp, struct rcu_exp_work, rew_work);
+	rcu_exp_sel_wait_wake(rewp->rew_s);
+}
+
+static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
+{
+	INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
+	queue_work(rcu_gp_wq, &rew->rew_work);
+}
+
+static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
+{
+	destroy_work_on_stack(&rew->rew_work);
+}
+#endif /* CONFIG_RCU_EXP_KTHREAD */
+
+/*
+ * Select the nodes that the upcoming expedited grace period needs
+ * to wait for.
+ */
+static void sync_rcu_exp_select_cpus(void)
+{
+	struct rcu_node *rnp;
+
+	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
+	sync_exp_reset_tree();
+	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
+
+	/* Schedule work for each leaf rcu_node structure. */
+	rcu_for_each_leaf_node(rnp) {
+		rnp->exp_need_flush = false;
+		if (!READ_ONCE(rnp->expmask))
+			continue; /* Avoid early boot non-existent wq. */
+		if (!rcu_gp_par_worker_started() ||
+		    rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
+		    rcu_is_last_leaf_node(rnp)) {
+			/* No worker started yet or last leaf, do direct call. */
+			sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
+			continue;
+		}
+		sync_rcu_exp_select_cpus_queue_work(rnp);
+		rnp->exp_need_flush = true;
+	}
+
+	/* Wait for jobs (if any) to complete. */
+	rcu_for_each_leaf_node(rnp)
+		if (rnp->exp_need_flush)
+			sync_rcu_exp_select_cpus_flush_work(rnp);
+}
+
+/*
+ * Wait for the expedited grace period to elapse, within time limit.
+ * If the time limit is exceeded without the grace period elapsing,
+ * return false, otherwise return true.
+ */
+static bool synchronize_rcu_expedited_wait_once(long tlimit)
+{
+	int t;
+	struct rcu_node *rnp_root = rcu_get_root();
+
+	t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
+					  sync_rcu_exp_done_unlocked(rnp_root),
+					  tlimit);
+	// Workqueues should not be signaled.
+	if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
+		return true;
+	WARN_ON(t < 0);  /* workqueues should not be signaled. */
+	return false;
+}
+
+/*
+ * Wait for the expedited grace period to elapse, issuing any needed
+ * RCU CPU stall warnings along the way.
+ */
+static void synchronize_rcu_expedited_wait(void)
+{
+	int cpu;
+	unsigned long j;
+	unsigned long jiffies_stall;
+	unsigned long jiffies_start;
+	unsigned long mask;
+	int ndetected;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	struct rcu_node *rnp_root = rcu_get_root();
+
+	trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
+	jiffies_stall = rcu_exp_jiffies_till_stall_check();
+	jiffies_start = jiffies;
+	if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
+		if (synchronize_rcu_expedited_wait_once(1))
+			return;
+		rcu_for_each_leaf_node(rnp) {
+			mask = READ_ONCE(rnp->expmask);
+			for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
+				rdp = per_cpu_ptr(&rcu_data, cpu);
+				if (rdp->rcu_forced_tick_exp)
+					continue;
+				rdp->rcu_forced_tick_exp = true;
+				preempt_disable();
+				if (cpu_online(cpu))
+					tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
+				preempt_enable();
+			}
+		}
+		j = READ_ONCE(jiffies_till_first_fqs);
+		if (synchronize_rcu_expedited_wait_once(j + HZ))
+			return;
+	}
+
+	for (;;) {
+		if (synchronize_rcu_expedited_wait_once(jiffies_stall))
+			return;
+		if (rcu_stall_is_suppressed())
+			continue;
+		trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
+		pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
+		       rcu_state.name);
+		ndetected = 0;
+		rcu_for_each_leaf_node(rnp) {
+			ndetected += rcu_print_task_exp_stall(rnp);
+			for_each_leaf_node_possible_cpu(rnp, cpu) {
+				struct rcu_data *rdp;
+
+				mask = leaf_node_cpu_bit(rnp, cpu);
+				if (!(READ_ONCE(rnp->expmask) & mask))
+					continue;
+				ndetected++;
+				rdp = per_cpu_ptr(&rcu_data, cpu);
+				pr_cont(" %d-%c%c%c%c", cpu,
+					"O."[!!cpu_online(cpu)],
+					"o."[!!(rdp->grpmask & rnp->expmaskinit)],
+					"N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
+					"D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
+			}
+		}
+		pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
+			jiffies - jiffies_start, rcu_state.expedited_sequence,
+			data_race(rnp_root->expmask),
+			".T"[!!data_race(rnp_root->exp_tasks)]);
+		if (ndetected) {
+			pr_err("blocking rcu_node structures (internal RCU debug):");
+			rcu_for_each_node_breadth_first(rnp) {
+				if (rnp == rnp_root)
+					continue; /* printed unconditionally */
+				if (sync_rcu_exp_done_unlocked(rnp))
+					continue;
+				pr_cont(" l=%u:%d-%d:%#lx/%c",
+					rnp->level, rnp->grplo, rnp->grphi,
+					data_race(rnp->expmask),
+					".T"[!!data_race(rnp->exp_tasks)]);
+			}
+			pr_cont("\n");
+		}
+		rcu_for_each_leaf_node(rnp) {
+			for_each_leaf_node_possible_cpu(rnp, cpu) {
+				mask = leaf_node_cpu_bit(rnp, cpu);
+				if (!(READ_ONCE(rnp->expmask) & mask))
+					continue;
+				preempt_disable(); // For smp_processor_id() in dump_cpu_task().
+				dump_cpu_task(cpu);
+				preempt_enable();
+			}
+		}
+		jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
+		panic_on_rcu_stall();
+	}
+}
+
+/*
+ * Wait for the current expedited grace period to complete, and then
+ * wake up everyone who piggybacked on the just-completed expedited
+ * grace period.  Also update all the ->exp_seq_rq counters as needed
+ * in order to avoid counter-wrap problems.
+ */
+static void rcu_exp_wait_wake(unsigned long s)
+{
+	struct rcu_node *rnp;
+
+	synchronize_rcu_expedited_wait();
+
+	// Switch over to wakeup mode, allowing the next GP to proceed.
+	// End the previous grace period only after acquiring the mutex
+	// to ensure that only one GP runs concurrently with wakeups.
+	mutex_lock(&rcu_state.exp_wake_mutex);
+	rcu_exp_gp_seq_end();
+	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
+
+	rcu_for_each_node_breadth_first(rnp) {
+		if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
+			spin_lock(&rnp->exp_lock);
+			/* Recheck, avoid hang in case someone just arrived. */
+			if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
+				WRITE_ONCE(rnp->exp_seq_rq, s);
+			spin_unlock(&rnp->exp_lock);
+		}
+		smp_mb(); /* All above changes before wakeup. */
+		wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
+	}
+	trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
+	mutex_unlock(&rcu_state.exp_wake_mutex);
+}
+
+/*
+ * Common code to drive an expedited grace period forward, used by
+ * workqueues and mid-boot-time tasks.
+ */
+static void rcu_exp_sel_wait_wake(unsigned long s)
+{
+	/* Initialize the rcu_node tree in preparation for the wait. */
+	sync_rcu_exp_select_cpus();
+
+	/* Wait and clean up, including waking everyone. */
+	rcu_exp_wait_wake(s);
+}
+
+#ifdef CONFIG_PREEMPT_RCU
+
+/*
+ * Remote handler for smp_call_function_single().  If there is an
+ * RCU read-side critical section in effect, request that the
+ * next rcu_read_unlock() record the quiescent state up the
+ * ->expmask fields in the rcu_node tree.  Otherwise, immediately
+ * report the quiescent state.
+ */
+static void rcu_exp_handler(void *unused)
+{
+	int depth = rcu_preempt_depth();
+	unsigned long flags;
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+	struct rcu_node *rnp = rdp->mynode;
+	struct task_struct *t = current;
+
+	/*
+	 * First, the common case of not being in an RCU read-side
+	 * critical section.  If also enabled or idle, immediately
+	 * report the quiescent state, otherwise defer.
+	 */
+	if (!depth) {
+		if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
+		    rcu_is_cpu_rrupt_from_idle()) {
+			rcu_report_exp_rdp(rdp);
+		} else {
+			WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
+			set_tsk_need_resched(t);
+			set_preempt_need_resched();
+		}
+		return;
+	}
+
+	/*
+	 * Second, the less-common case of being in an RCU read-side
+	 * critical section.  In this case we can count on a future
+	 * rcu_read_unlock().  However, this rcu_read_unlock() might
+	 * execute on some other CPU, but in that case there will be
+	 * a future context switch.  Either way, if the expedited
+	 * grace period is still waiting on this CPU, set ->deferred_qs
+	 * so that the eventual quiescent state will be reported.
+	 * Note that there is a large group of race conditions that
+	 * can have caused this quiescent state to already have been
+	 * reported, so we really do need to check ->expmask.
+	 */
+	if (depth > 0) {
+		raw_spin_lock_irqsave_rcu_node(rnp, flags);
+		if (rnp->expmask & rdp->grpmask) {
+			WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
+			t->rcu_read_unlock_special.b.exp_hint = true;
+		}
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return;
+	}
+
+	// Finally, negative nesting depth should not happen.
+	WARN_ON_ONCE(1);
+}
+
+/* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
+static void sync_sched_exp_online_cleanup(int cpu)
+{
+}
+
+/*
+ * Scan the current list of tasks blocked within RCU read-side critical
+ * sections, printing out the tid of each that is blocking the current
+ * expedited grace period.
+ */
+static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+{
+	unsigned long flags;
+	int ndetected = 0;
+	struct task_struct *t;
+
+	raw_spin_lock_irqsave_rcu_node(rnp, flags);
+	if (!rnp->exp_tasks) {
+		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+		return 0;
+	}
+	t = list_entry(rnp->exp_tasks->prev,
+		       struct task_struct, rcu_node_entry);
+	list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
+		pr_cont(" P%d", t->pid);
+		ndetected++;
+	}
+	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+	return ndetected;
+}
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/* Request an expedited quiescent state. */
+static void rcu_exp_need_qs(void)
+{
+	__this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
+	/* Store .exp before .rcu_urgent_qs. */
+	smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
+	set_tsk_need_resched(current);
+	set_preempt_need_resched();
+}
+
+/* Invoked on each online non-idle CPU for expedited quiescent state. */
+static void rcu_exp_handler(void *unused)
+{
+	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
+	struct rcu_node *rnp = rdp->mynode;
+	bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
+
+	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
+	    __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
+		return;
+	if (rcu_is_cpu_rrupt_from_idle() ||
+	    (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
+		rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
+		return;
+	}
+	rcu_exp_need_qs();
+}
+
+/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
+static void sync_sched_exp_online_cleanup(int cpu)
+{
+	unsigned long flags;
+	int my_cpu;
+	struct rcu_data *rdp;
+	int ret;
+	struct rcu_node *rnp;
+
+	rdp = per_cpu_ptr(&rcu_data, cpu);
+	rnp = rdp->mynode;
+	my_cpu = get_cpu();
+	/* Quiescent state either not needed or already requested, leave. */
+	if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
+	    READ_ONCE(rdp->cpu_no_qs.b.exp)) {
+		put_cpu();
+		return;
+	}
+	/* Quiescent state needed on current CPU, so set it up locally. */
+	if (my_cpu == cpu) {
+		local_irq_save(flags);
+		rcu_exp_need_qs();
+		local_irq_restore(flags);
+		put_cpu();
+		return;
+	}
+	/* Quiescent state needed on some other CPU, send IPI. */
+	ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
+	put_cpu();
+	WARN_ON_ONCE(ret);
+}
+
+/*
+ * Because preemptible RCU does not exist, we never have to check for
+ * tasks blocked within RCU read-side critical sections that are
+ * blocking the current expedited grace period.
+ */
+static int rcu_print_task_exp_stall(struct rcu_node *rnp)
+{
+	return 0;
+}
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
+
+/**
+ * synchronize_rcu_expedited - Brute-force RCU grace period
+ *
+ * Wait for an RCU grace period, but expedite it.  The basic idea is to
+ * IPI all non-idle non-nohz online CPUs.  The IPI handler checks whether
+ * the CPU is in an RCU critical section, and if so, it sets a flag that
+ * causes the outermost rcu_read_unlock() to report the quiescent state
+ * for RCU-preempt or asks the scheduler for help for RCU-sched.  On the
+ * other hand, if the CPU is not in an RCU read-side critical section,
+ * the IPI handler reports the quiescent state immediately.
+ *
+ * Although this is a great improvement over previous expedited
+ * implementations, it is still unfriendly to real-time workloads, so is
+ * thus not recommended for any sort of common-case code.  In fact, if
+ * you are using synchronize_rcu_expedited() in a loop, please restructure
+ * your code to batch your updates, and then use a single synchronize_rcu()
+ * instead.
+ *
+ * This has the same semantics as (but is more brutal than) synchronize_rcu().
+ */
+void synchronize_rcu_expedited(void)
+{
+	bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
+	unsigned long flags;
+	struct rcu_exp_work rew;
+	struct rcu_node *rnp;
+	unsigned long s;
+
+	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_expedited() in RCU read-side critical section");
+
+	/* Is the state is such that the call is a grace period? */
+	if (rcu_blocking_is_gp()) {
+		// Note well that this code runs with !PREEMPT && !SMP.
+		// In addition, all code that advances grace periods runs
+		// at process level.  Therefore, this expedited GP overlaps
+		// with other expedited GPs only by being fully nested within
+		// them, which allows reuse of ->gp_seq_polled_exp_snap.
+		rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
+		rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
+
+		local_irq_save(flags);
+		WARN_ON_ONCE(num_online_cpus() > 1);
+		rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT);
+		local_irq_restore(flags);
+		return;  // Context allows vacuous grace periods.
+	}
+
+	/* If expedited grace periods are prohibited, fall back to normal. */
+	if (rcu_gp_is_normal()) {
+		wait_rcu_gp(call_rcu);
+		return;
+	}
+
+	/* Take a snapshot of the sequence number.  */
+	s = rcu_exp_gp_seq_snap();
+	if (exp_funnel_lock(s))
+		return;  /* Someone else did our work for us. */
+
+	/* Ensure that load happens before action based on it. */
+	if (unlikely(boottime)) {
+		/* Direct call during scheduler init and early_initcalls(). */
+		rcu_exp_sel_wait_wake(s);
+	} else {
+		/* Marshall arguments & schedule the expedited grace period. */
+		rew.rew_s = s;
+		synchronize_rcu_expedited_queue_work(&rew);
+	}
+
+	/* Wait for expedited grace period to complete. */
+	rnp = rcu_get_root();
+	wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
+		   sync_exp_work_done(s));
+	smp_mb(); /* Work actions happen before return. */
+
+	/* Let the next expedited grace period start. */
+	mutex_unlock(&rcu_state.exp_mutex);
+
+	if (likely(!boottime))
+		synchronize_rcu_expedited_destroy_work(&rew);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+/*
+ * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
+ * RCU grace periods that it needs.
+ */
+static void sync_rcu_do_polled_gp(struct work_struct *wp)
+{
+	unsigned long flags;
+	int i = 0;
+	struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
+	unsigned long s;
+
+	raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+	s = rnp->exp_seq_poll_rq;
+	rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+	raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+	if (s == RCU_GET_STATE_COMPLETED)
+		return;
+	while (!poll_state_synchronize_rcu(s)) {
+		synchronize_rcu_expedited();
+		if (i == 10 || i == 20)
+			pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
+		i++;
+	}
+	raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+	s = rnp->exp_seq_poll_rq;
+	if (poll_state_synchronize_rcu(s))
+		rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
+	raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+}
+
+/**
+ * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
+ *
+ * Returns a cookie to pass to a call to cond_synchronize_rcu(),
+ * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
+ * allowing them to determine whether or not any sort of grace period has
+ * elapsed in the meantime.  If the needed expedited grace period is not
+ * already slated to start, initiates that grace period.
+ */
+unsigned long start_poll_synchronize_rcu_expedited(void)
+{
+	unsigned long flags;
+	struct rcu_data *rdp;
+	struct rcu_node *rnp;
+	unsigned long s;
+
+	s = get_state_synchronize_rcu();
+	rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
+	rnp = rdp->mynode;
+	if (rcu_init_invoked())
+		raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
+	if (!poll_state_synchronize_rcu(s)) {
+		rnp->exp_seq_poll_rq = s;
+		if (rcu_init_invoked())
+			queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
+	}
+	if (rcu_init_invoked())
+		raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
+
+	return s;
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
+
+/**
+ * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
+ * @rgosp: Place to put snapshot of 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.
+ * If the needed expedited grace period is not already slated to start,
+ * initiates that grace period.
+ */
+void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
+{
+	get_state_synchronize_rcu_full(rgosp);
+	(void)start_poll_synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
+
+/**
+ * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
+ *
+ * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
+ *
+ * If any type of full RCU grace period has elapsed since the earlier
+ * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
+ * or start_poll_synchronize_rcu_expedited(), just return.  Otherwise,
+ * invoke synchronize_rcu_expedited() 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_expedited(unsigned long oldstate)
+{
+	if (!poll_state_synchronize_rcu(oldstate))
+		synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
+
+/**
+ * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited 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_expedited()
+ * 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_expedited_full(struct rcu_gp_oldstate *rgosp)
+{
+	if (!poll_state_synchronize_rcu_full(rgosp))
+		synchronize_rcu_expedited();
+}
+EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);