Merge branches 'doc.2017.08.17a', 'fixes.2017.08.17a', 'hotplug.2017.07.25b', 'misc.2017.08.17a', 'spin_unlock_wait_no.2017.08.17a', 'srcu.2017.07.27c' and 'torture.2017.07.24c' into HEAD

doc.2017.08.17a: Documentation updates.
fixes.2017.08.17a: RCU fixes.
hotplug.2017.07.25b: CPU-hotplug updates.
misc.2017.08.17a: Miscellaneous fixes outside of RCU (give or take conflicts).
spin_unlock_wait_no.2017.08.17a: Remove spin_unlock_wait().
srcu.2017.07.27c: SRCU updates.
torture.2017.07.24c: Torture-test updates.

kernel/rcu/tree_plugin.h

@@ -180,6 +180,8 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 	struct task_struct *t = current;
 
 	lockdep_assert_held(&rnp->lock);
+	WARN_ON_ONCE(rdp->mynode != rnp);
+	WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
 
 	/*
 	 * Decide where to queue the newly blocked task.  In theory,
@@ -261,6 +263,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 		rnp->gp_tasks = &t->rcu_node_entry;
 	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
 		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. */
 
 	/*
@@ -482,6 +488,7 @@ void rcu_read_unlock_special(struct task_struct *t)
 		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(rnp->level != rcu_num_lvls - 1);
 		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
 		empty_exp = sync_rcu_preempt_exp_done(rnp);
 		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
@@ -495,10 +502,10 @@ void rcu_read_unlock_special(struct task_struct *t)
 		if (&t->rcu_node_entry == rnp->exp_tasks)
 			rnp->exp_tasks = np;
 		if (IS_ENABLED(CONFIG_RCU_BOOST)) {
-			if (&t->rcu_node_entry == rnp->boost_tasks)
-				rnp->boost_tasks = np;
 			/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
 			drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
+			if (&t->rcu_node_entry == rnp->boost_tasks)
+				rnp->boost_tasks = np;
 		}
 
 		/*
@@ -636,10 +643,17 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp)
  */
 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");
 	WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
-	if (rcu_preempt_has_tasks(rnp))
+	if (rcu_preempt_has_tasks(rnp)) {
 		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->gpnum, t->pid);
+	}
 	WARN_ON_ONCE(rnp->qsmask);
 }
 
@@ -1788,22 +1802,61 @@ bool rcu_is_nocb_cpu(int cpu)
 }
 
 /*
- * Kick the leader kthread for this NOCB group.
+ * Kick the leader kthread for this NOCB group.  Caller holds ->nocb_lock
+ * and this function releases it.
  */
-static void wake_nocb_leader(struct rcu_data *rdp, bool force)
+static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
+			       unsigned long flags)
+	__releases(rdp->nocb_lock)
 {
 	struct rcu_data *rdp_leader = rdp->nocb_leader;
 
-	if (!READ_ONCE(rdp_leader->nocb_kthread))
+	lockdep_assert_held(&rdp->nocb_lock);
+	if (!READ_ONCE(rdp_leader->nocb_kthread)) {
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 		return;
-	if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) {
+	}
+	if (rdp_leader->nocb_leader_sleep || force) {
 		/* Prior smp_mb__after_atomic() orders against prior enqueue. */
 		WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
+		del_timer(&rdp->nocb_timer);
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 		smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
 		swake_up(&rdp_leader->nocb_wq);
+	} else {
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 	}
 }
 
+/*
+ * Kick the leader kthread for this NOCB group, but caller has not
+ * acquired locks.
+ */
+static void wake_nocb_leader(struct rcu_data *rdp, bool force)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+	__wake_nocb_leader(rdp, force, flags);
+}
+
+/*
+ * Arrange to wake the leader kthread for this NOCB group at some
+ * future time when it is safe to do so.
+ */
+static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
+				   const char *reason)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+	if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
+		mod_timer(&rdp->nocb_timer, jiffies + 1);
+	WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
+	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
+	raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
+}
+
 /*
  * Does the specified CPU need an RCU callback for the specified flavor
  * of rcu_barrier()?
@@ -1891,11 +1944,8 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeEmpty"));
 		} else {
-			WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE);
-			/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
-			smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
-			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
-					    TPS("WakeEmptyIsDeferred"));
+			wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
+					       TPS("WakeEmptyIsDeferred"));
 		}
 		rdp->qlen_last_fqs_check = 0;
 	} else if (len > rdp->qlen_last_fqs_check + qhimark) {
@@ -1905,11 +1955,8 @@ static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
 			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
 					    TPS("WakeOvf"));
 		} else {
-			WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_FORCE);
-			/* Store ->nocb_defer_wakeup before ->rcu_urgent_qs. */
-			smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
-			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
-					    TPS("WakeOvfIsDeferred"));
+			wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
+					       TPS("WakeOvfIsDeferred"));
 		}
 		rdp->qlen_last_fqs_check = LONG_MAX / 2;
 	} else {
@@ -1961,30 +2008,19 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
  * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
  * not a no-CBs CPU.
  */
-static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
 						     struct rcu_data *rdp,
 						     unsigned long flags)
 {
-	long ql = rsp->orphan_done.len;
-	long qll = rsp->orphan_done.len_lazy;
-
-	/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
+	RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_nocb_adopt_orphan_cbs() invoked with irqs enabled!!!");
 	if (!rcu_is_nocb_cpu(smp_processor_id()))
-		return false;
-
-	/* First, enqueue the donelist, if any.  This preserves CB ordering. */
-	if (rsp->orphan_done.head) {
-		__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_done),
-					rcu_cblist_tail(&rsp->orphan_done),
-					ql, qll, flags);
-	}
-	if (rsp->orphan_pend.head) {
-		__call_rcu_nocb_enqueue(rdp, rcu_cblist_head(&rsp->orphan_pend),
-					rcu_cblist_tail(&rsp->orphan_pend),
-					ql, qll, flags);
-	}
-	rcu_cblist_init(&rsp->orphan_done);
-	rcu_cblist_init(&rsp->orphan_pend);
+		return false; /* Not NOCBs CPU, caller must migrate CBs. */
+	__call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
+				rcu_segcblist_tail(&rdp->cblist),
+				rcu_segcblist_n_cbs(&rdp->cblist),
+				rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
+	rcu_segcblist_init(&rdp->cblist);
+	rcu_segcblist_disable(&rdp->cblist);
 	return true;
 }
 
@@ -2031,6 +2067,7 @@ static void rcu_nocb_wait_gp(struct rcu_data *rdp)
 static void nocb_leader_wait(struct rcu_data *my_rdp)
 {
 	bool firsttime = true;
+	unsigned long flags;
 	bool gotcbs;
 	struct rcu_data *rdp;
 	struct rcu_head **tail;
@@ -2039,13 +2076,17 @@ wait_again:
 
 	/* Wait for callbacks to appear. */
 	if (!rcu_nocb_poll) {
-		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep");
+		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
 		swait_event_interruptible(my_rdp->nocb_wq,
 				!READ_ONCE(my_rdp->nocb_leader_sleep));
-		/* Memory barrier handled by smp_mb() calls below and repoll. */
+		raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
+		my_rdp->nocb_leader_sleep = true;
+		WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
+		del_timer(&my_rdp->nocb_timer);
+		raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
 	} else if (firsttime) {
 		firsttime = false; /* Don't drown trace log with "Poll"! */
-		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll");
+		trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
 	}
 
 	/*
@@ -2054,7 +2095,7 @@ wait_again:
 	 * nocb_gp_head, where they await a grace period.
 	 */
 	gotcbs = false;
-	smp_mb(); /* wakeup before ->nocb_head reads. */
+	smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
 	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
 		rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
 		if (!rdp->nocb_gp_head)
@@ -2066,56 +2107,41 @@ wait_again:
 		gotcbs = true;
 	}
 
-	/*
-	 * If there were no callbacks, sleep a bit, rescan after a
-	 * memory barrier, and go retry.
-	 */
+	/* No callbacks?  Sleep a bit if polling, and go retry.  */
 	if (unlikely(!gotcbs)) {
-		if (!rcu_nocb_poll)
-			trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
-					    "WokeEmpty");
 		WARN_ON(signal_pending(current));
-		schedule_timeout_interruptible(1);
-
-		/* Rescan in case we were a victim of memory ordering. */
-		my_rdp->nocb_leader_sleep = true;
-		smp_mb();  /* Ensure _sleep true before scan. */
-		for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower)
-			if (READ_ONCE(rdp->nocb_head)) {
-				/* Found CB, so short-circuit next wait. */
-				my_rdp->nocb_leader_sleep = false;
-				break;
-			}
+		if (rcu_nocb_poll) {
+			schedule_timeout_interruptible(1);
+		} else {
+			trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
+					    TPS("WokeEmpty"));
+		}
 		goto wait_again;
 	}
 
 	/* Wait for one grace period. */
 	rcu_nocb_wait_gp(my_rdp);
 
-	/*
-	 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
-	 * We set it now, but recheck for new callbacks while
-	 * traversing our follower list.
-	 */
-	my_rdp->nocb_leader_sleep = true;
-	smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
-
 	/* Each pass through the following loop wakes a follower, if needed. */
 	for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
-		if (READ_ONCE(rdp->nocb_head))
+		if (!rcu_nocb_poll &&
+		    READ_ONCE(rdp->nocb_head) &&
+		    READ_ONCE(my_rdp->nocb_leader_sleep)) {
+			raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
 			my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
+			raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
+		}
 		if (!rdp->nocb_gp_head)
 			continue; /* No CBs, so no need to wake follower. */
 
 		/* Append callbacks to follower's "done" list. */
-		tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail);
+		raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+		tail = rdp->nocb_follower_tail;
+		rdp->nocb_follower_tail = rdp->nocb_gp_tail;
 		*tail = rdp->nocb_gp_head;
-		smp_mb__after_atomic(); /* Store *tail before wakeup. */
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 		if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
-			/*
-			 * List was empty, wake up the follower.
-			 * Memory barriers supplied by atomic_long_add().
-			 */
+			/* List was empty, so wake up the follower.  */
 			swake_up(&rdp->nocb_wq);
 		}
 	}
@@ -2131,28 +2157,16 @@ wait_again:
  */
 static void nocb_follower_wait(struct rcu_data *rdp)
 {
-	bool firsttime = true;
-
 	for (;;) {
-		if (!rcu_nocb_poll) {
-			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
-					    "FollowerSleep");
-			swait_event_interruptible(rdp->nocb_wq,
-						 READ_ONCE(rdp->nocb_follower_head));
-		} else if (firsttime) {
-			/* Don't drown trace log with "Poll"! */
-			firsttime = false;
-			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll");
-		}
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
+		swait_event_interruptible(rdp->nocb_wq,
+					 READ_ONCE(rdp->nocb_follower_head));
 		if (smp_load_acquire(&rdp->nocb_follower_head)) {
 			/* ^^^ Ensure CB invocation follows _head test. */
 			return;
 		}
-		if (!rcu_nocb_poll)
-			trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
-					    "WokeEmpty");
 		WARN_ON(signal_pending(current));
-		schedule_timeout_interruptible(1);
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
 	}
 }
 
@@ -2165,6 +2179,7 @@ static void nocb_follower_wait(struct rcu_data *rdp)
 static int rcu_nocb_kthread(void *arg)
 {
 	int c, cl;
+	unsigned long flags;
 	struct rcu_head *list;
 	struct rcu_head *next;
 	struct rcu_head **tail;
@@ -2179,11 +2194,14 @@ static int rcu_nocb_kthread(void *arg)
 			nocb_follower_wait(rdp);
 
 		/* Pull the ready-to-invoke callbacks onto local list. */
-		list = READ_ONCE(rdp->nocb_follower_head);
+		raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+		list = rdp->nocb_follower_head;
+		rdp->nocb_follower_head = NULL;
+		tail = rdp->nocb_follower_tail;
+		rdp->nocb_follower_tail = &rdp->nocb_follower_head;
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 		BUG_ON(!list);
-		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty");
-		WRITE_ONCE(rdp->nocb_follower_head, NULL);
-		tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head);
+		trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
 
 		/* Each pass through the following loop invokes a callback. */
 		trace_rcu_batch_start(rdp->rsp->name,
@@ -2226,18 +2244,39 @@ static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
 }
 
 /* Do a deferred wakeup of rcu_nocb_kthread(). */
-static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
 {
+	unsigned long flags;
 	int ndw;
 
-	if (!rcu_nocb_need_deferred_wakeup(rdp))
+	raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
+	if (!rcu_nocb_need_deferred_wakeup(rdp)) {
+		raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
 		return;
+	}
 	ndw = READ_ONCE(rdp->nocb_defer_wakeup);
 	WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
-	wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE);
+	__wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
 	trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
 }
 
+/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
+static void do_nocb_deferred_wakeup_timer(unsigned long x)
+{
+	do_nocb_deferred_wakeup_common((struct rcu_data *)x);
+}
+
+/*
+ * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
+ * This means we do an inexact common-case check.  Note that if
+ * we miss, ->nocb_timer will eventually clean things up.
+ */
+static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
+{
+	if (rcu_nocb_need_deferred_wakeup(rdp))
+		do_nocb_deferred_wakeup_common(rdp);
+}
+
 void __init rcu_init_nohz(void)
 {
 	int cpu;
@@ -2287,6 +2326,9 @@ static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
 	rdp->nocb_tail = &rdp->nocb_head;
 	init_swait_queue_head(&rdp->nocb_wq);
 	rdp->nocb_follower_tail = &rdp->nocb_follower_head;
+	raw_spin_lock_init(&rdp->nocb_lock);
+	setup_timer(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer,
+		    (unsigned long)rdp);
 }
 
 /*
@@ -2459,7 +2501,7 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
 	return false;
 }
 
-static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
+static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
 						     struct rcu_data *rdp,
 						     unsigned long flags)
 {