5 files changed, 19 insertions, 17 deletions

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 07a6a183c5..7567ca8e74 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -3874,7 +3874,9 @@ rcu_torture_init(void)
 	}
 	if (fqs_duration < 0)
 		fqs_duration = 0;
-	if (fqs_duration) {
+	if (fqs_holdoff < 0)
+		fqs_holdoff = 0;
+	if (fqs_duration && fqs_holdoff) {
 		/* Create the fqs thread */
 		firsterr = torture_create_kthread(rcu_torture_fqs, NULL,
 						  fqs_task);
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 560e99ec53..0351a4e835 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -772,20 +772,10 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock_nmisafe);
  */
 static void srcu_gp_start(struct srcu_struct *ssp)
 {
-	struct srcu_data *sdp;
 	int state;
 
-	if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
-		sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
-	else
-		sdp = this_cpu_ptr(ssp->sda);
 	lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock));
 	WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed));
-	spin_lock_rcu_node(sdp);  /* Interrupts already disabled. */
-	rcu_segcblist_advance(&sdp->srcu_cblist,
-			      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
-	WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));
-	spin_unlock_rcu_node(sdp);  /* Interrupts remain disabled. */
 	WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies);
 	WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0);
 	smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
@@ -1271,9 +1261,11 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 	 *     period (gp_num = X + 8). So acceleration fails.
 	 */
 	s = rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq);
-	rcu_segcblist_advance(&sdp->srcu_cblist,
-			      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
-	WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s) && rhp);
+	if (rhp) {
+		rcu_segcblist_advance(&sdp->srcu_cblist,
+				      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
+		WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s));
+	}
 	if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
 		sdp->srcu_gp_seq_needed = s;
 		needgp = true;
@@ -1723,6 +1715,11 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 	WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL));
 	rcu_segcblist_advance(&sdp->srcu_cblist,
 			      rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq));
+	/*
+	 * Although this function is theoretically re-entrant, concurrent
+	 * callbacks invocation is disallowed to avoid executing an SRCU barrier
+	 * too early.
+	 */
 	if (sdp->srcu_cblist_invoking ||
 	    !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) {
 		spin_unlock_irq_rcu_node(sdp);
@@ -1753,6 +1750,7 @@ static void srcu_invoke_callbacks(struct work_struct *work)
 	sdp->srcu_cblist_invoking = false;
 	more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist);
 	spin_unlock_irq_rcu_node(sdp);
+	/* An SRCU barrier or callbacks from previous nesting work pending */
 	if (more)
 		srcu_schedule_cbs_sdp(sdp, 0);
 }
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index f54d5782ec..732ad5b399 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -975,7 +975,7 @@ static void check_holdout_task(struct task_struct *t,
 	    t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
 	    !rcu_tasks_is_holdout(t) ||
 	    (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
-	     !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
+	     !is_idle_task(t) && READ_ONCE(t->rcu_tasks_idle_cpu) >= 0)) {
 		WRITE_ONCE(t->rcu_tasks_holdout, false);
 		list_del_init(&t->rcu_tasks_holdout_list);
 		put_task_struct(t);
@@ -993,7 +993,7 @@ static void check_holdout_task(struct task_struct *t,
 		 t, ".I"[is_idle_task(t)],
 		 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
 		 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
-		 t->rcu_tasks_idle_cpu, cpu);
+		 data_race(t->rcu_tasks_idle_cpu), cpu);
 	sched_show_task(t);
 }
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f544f24df1..f2c10d351b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2370,6 +2370,8 @@ void rcu_force_quiescent_state(void)
 	struct rcu_node *rnp;
 	struct rcu_node *rnp_old = NULL;
 
+	if (!rcu_gp_in_progress())
+		return;
 	/* Funnel through hierarchy to reduce memory contention. */
 	rnp = raw_cpu_read(rcu_data.mynode);
 	for (; rnp != NULL; rnp = rnp->parent) {
diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 4efbf7333d..d430b4656f 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1383,7 +1383,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 			rcu_nocb_unlock_irqrestore(rdp, flags);
 			continue;
 		}
-		WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
+		rcu_nocb_try_flush_bypass(rdp, jiffies);
 		rcu_nocb_unlock_irqrestore(rdp, flags);
 		wake_nocb_gp(rdp, false);
 		sc->nr_to_scan -= _count;