Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU updates from Ingo Molnar:
 "The main changes in this cycle were:

   - Make kfree_rcu() use kfree_bulk() for added performance

   - RCU updates

   - Callback-overload handling updates

   - Tasks-RCU KCSAN and sparse updates

   - Locking torture test and RCU torture test updates

   - Documentation updates

   - Miscellaneous fixes"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (74 commits)
  rcu: Make rcu_barrier() account for offline no-CBs CPUs
  rcu: Mark rcu_state.gp_seq to detect concurrent writes
  Documentation/memory-barriers: Fix typos
  doc: Add rcutorture scripting to torture.txt
  doc/RCU/rcu: Use https instead of http if possible
  doc/RCU/rcu: Use absolute paths for non-rst files
  doc/RCU/rcu: Use ':ref:' for links to other docs
  doc/RCU/listRCU: Update example function name
  doc/RCU/listRCU: Fix typos in a example code snippets
  doc/RCU/Design: Remove remaining HTML tags in ReST files
  doc: Add some more RCU list patterns in the kernel
  rcutorture: Set KCSAN Kconfig options to detect more data races
  rcutorture: Manually clean up after rcu_barrier() failure
  rcutorture: Make rcu_torture_barrier_cbs() post from corresponding CPU
  rcuperf: Measure memory footprint during kfree_rcu() test
  rcutorture: Annotation lockless accesses to rcu_torture_current
  rcutorture: Add READ_ONCE() to rcu_torture_count and rcu_torture_batch
  rcutorture: Fix stray access to rcu_fwd_cb_nodelay
  rcutorture: Fix rcu_torture_one_read()/rcu_torture_writer() data race
  rcutorture: Make kvm-find-errors.sh abort on bad directory
  ...

1 files changed, 16 insertions, 9 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index c6ea81cd4189..097635c41135 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -56,6 +56,8 @@ static void __init rcu_bootup_announce_oddness(void)
 		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)
@@ -753,7 +755,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
 	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)rnp->gp_seq, (long)rnp->completedqs);
+		(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);
@@ -1032,18 +1034,18 @@ static int rcu_boost_kthread(void *arg)
 
 	trace_rcu_utilization(TPS("Start boost kthread@init"));
 	for (;;) {
-		rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
+		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
 		trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
 		rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
 		trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
-		rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
+		WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
 		more2boost = rcu_boost(rnp);
 		if (more2boost)
 			spincnt++;
 		else
 			spincnt = 0;
 		if (spincnt > 10) {
-			rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
+			WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
 			trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
 			schedule_timeout_interruptible(2);
 			trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
@@ -1077,12 +1079,12 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
 	    (rnp->gp_tasks != NULL &&
 	     rnp->boost_tasks == NULL &&
 	     rnp->qsmask == 0 &&
-	     ULONG_CMP_GE(jiffies, rnp->boost_time))) {
+	     (ULONG_CMP_GE(jiffies, rnp->boost_time) || rcu_state.cbovld))) {
 		if (rnp->exp_tasks == NULL)
 			rnp->boost_tasks = rnp->gp_tasks;
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 		rcu_wake_cond(rnp->boost_kthread_task,
-			      rnp->boost_kthread_status);
+			      READ_ONCE(rnp->boost_kthread_status));
 	} else {
 		raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 	}
@@ -1486,6 +1488,7 @@ module_param(nocb_nobypass_lim_per_jiffy, int, 0);
  * flag the contention.
  */
 static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
+	__acquires(&rdp->nocb_bypass_lock)
 {
 	lockdep_assert_irqs_disabled();
 	if (raw_spin_trylock(&rdp->nocb_bypass_lock))
@@ -1529,6 +1532,7 @@ static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
  * Release the specified rcu_data structure's ->nocb_bypass_lock.
  */
 static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
+	__releases(&rdp->nocb_bypass_lock)
 {
 	lockdep_assert_irqs_disabled();
 	raw_spin_unlock(&rdp->nocb_bypass_lock);
@@ -1577,8 +1581,7 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
 {
 	lockdep_assert_irqs_disabled();
-	if (rcu_segcblist_is_offloaded(&rdp->cblist) &&
-	    cpu_online(rdp->cpu))
+	if (rcu_segcblist_is_offloaded(&rdp->cblist))
 		lockdep_assert_held(&rdp->nocb_lock);
 }
 
@@ -1930,6 +1933,7 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
 	unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
+	bool wasempty = false;
 
 	/*
 	 * Each pass through the following loop checks for CBs and for the
@@ -1969,10 +1973,13 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
 		     rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
 			raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
 			needwake_gp = rcu_advance_cbs(rnp, rdp);
+			wasempty = rcu_segcblist_restempty(&rdp->cblist,
+							   RCU_NEXT_READY_TAIL);
 			raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
 		}
 		// Need to wait on some grace period?
-		WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp->cblist,
+		WARN_ON_ONCE(wasempty &&
+			     !rcu_segcblist_restempty(&rdp->cblist,
 						      RCU_NEXT_READY_TAIL));
 		if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
 			if (!needwait_gp ||