[PATCH 14/14] sched,lockdep: Employ lock pinning

[Peter Zijlstra]

Employ the new lockdep lock pinning annotation to ensure no
'accidental' lock-breaks happen with rq->lock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 kernel/sched/core.c     |   42 +++++++++++++++++++++++++++++++++++++++---
 kernel/sched/deadline.c |    8 ++++++++
 kernel/sched/fair.c     |   11 ++++++++---
 kernel/sched/rt.c       |    8 ++++++++
 kernel/sched/sched.h    |   10 ++++++++--
 5 files changed, 71 insertions(+), 8 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1201,8 +1201,15 @@ int set_cpus_allowed_ptr(struct task_str
 		stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
 		tlb_migrate_finish(p->mm);
 		return 0;
-	} else if (task_on_rq_queued(p))
+	} else if (task_on_rq_queued(p)) {
+		/*
+		 * OK, since we're going to drop the lock immediately
+		 * afterwards anyway.
+		 */
+		lockdep_unpin_lock(&rq->lock);
 		rq = move_queued_task(rq, p, dest_cpu);
+		lockdep_pin_lock(&rq->lock);
+	}
 out:
 	task_rq_unlock(rq, p, &flags);
 
@@ -1562,6 +1569,8 @@ static int select_fallback_rq(int cpu, s
 static inline
 int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)
 {
+	lockdep_assert_held(&p->pi_lock);
+
 	if (p->nr_cpus_allowed > 1)
 		cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);
 
@@ -1652,9 +1661,12 @@ ttwu_do_wakeup(struct rq *rq, struct tas
 #ifdef CONFIG_SMP
 	if (p->sched_class->task_woken) {
 		/*
-		 * XXX can drop rq->lock; most likely ok.
+		 * Our task @p is fully woken up and running; so its safe to
+		 * drop the rq->lock, hereafter rq is only used for statistics.
 		 */
+		lockdep_unpin_lock(&rq->lock);
 		p->sched_class->task_woken(rq, p);
+		lockdep_pin_lock(&rq->lock);
 	}
 
 	if (rq->idle_stamp) {
@@ -1674,6 +1686,8 @@ ttwu_do_wakeup(struct rq *rq, struct tas
 static void
 ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags)
 {
+	lockdep_assert_held(&rq->lock);
+
 #ifdef CONFIG_SMP
 	if (p->sched_contributes_to_load)
 		rq->nr_uninterruptible--;
@@ -1718,6 +1732,7 @@ void sched_ttwu_pending(void)
 		return;
 
 	raw_spin_lock_irqsave(&rq->lock, flags);
+	lockdep_pin_lock(&rq->lock);
 
 	while (llist) {
 		p = llist_entry(llist, struct task_struct, wake_entry);
@@ -1725,6 +1740,7 @@ void sched_ttwu_pending(void)
 		ttwu_do_activate(rq, p, 0);
 	}
 
+	lockdep_unpin_lock(&rq->lock);
 	raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
@@ -1821,7 +1837,9 @@ static void ttwu_queue(struct task_struc
 #endif
 
 	raw_spin_lock(&rq->lock);
+	lockdep_pin_lock(&rq->lock);
 	ttwu_do_activate(rq, p, 0);
+	lockdep_unpin_lock(&rq->lock);
 	raw_spin_unlock(&rq->lock);
 }
 
@@ -1916,9 +1934,17 @@ static void try_to_wake_up_local(struct
 	lockdep_assert_held(&rq->lock);
 
 	if (!raw_spin_trylock(&p->pi_lock)) {
+		/*
+		 * This is OK, because current is on_cpu, which avoids it being
+		 * picked for load-balance and preemption/IRQs are still
+		 * disabled avoiding further scheduler activity on it and we've
+		 * not yet picked a replacement task.
+		 */
+		lockdep_unpin_lock(&rq->lock);
 		raw_spin_unlock(&rq->lock);
 		raw_spin_lock(&p->pi_lock);
 		raw_spin_lock(&rq->lock);
+		lockdep_pin_lock(&rq->lock);
 	}
 
 	if (!(p->state & TASK_NORMAL))
@@ -2538,6 +2564,7 @@ context_switch(struct rq *rq, struct tas
 	 * of the scheduler it's an obvious special-case), so we
 	 * do an early lockdep release here:
 	 */
+	lockdep_unpin_lock(&rq->lock);
 	spin_release(&rq->lock.dep_map, 1, _THIS_IP_);
 
 	/* Here we just switch the register state and the stack. */
@@ -2960,6 +2987,7 @@ static void __sched __schedule(void)
 	 */
 	smp_mb__before_spinlock();
 	raw_spin_lock_irq(&rq->lock);
+	lockdep_pin_lock(&rq->lock);
 
 	rq->clock_skip_update <<= 1; /* promote REQ to ACT */
 
@@ -3002,8 +3030,10 @@ static void __sched __schedule(void)
 
 		rq = context_switch(rq, prev, next); /* unlocks the rq */
 		cpu = cpu_of(rq);
-	} else
+	} else {
+		lockdep_unpin_lock(&rq->lock);
 		raw_spin_unlock_irq(&rq->lock);
+	}
 
 	balance_callback(rq);
 }
@@ -5071,6 +5101,11 @@ static void migrate_tasks(struct rq *dea
 		if (rq->nr_running == 1)
 			break;
 
+		/*
+		 * Ensure rq->lock covers the entire task selection
+		 * until the migration.
+		 */
+		lockdep_pin_lock(&rq->lock);
 		next = pick_next_task(rq, &fake_task);
 		BUG_ON(!next);
 		next->sched_class->put_prev_task(rq, next);
@@ -5078,6 +5113,7 @@ static void migrate_tasks(struct rq *dea
 		/* Find suitable destination for @next, with force if needed. */
 		dest_cpu = select_fallback_rq(dead_rq->cpu, next);
 
+		lockdep_unpin_lock(&rq->lock);
 		rq = __migrate_task(rq, next, dest_cpu);
 		if (rq != dead_rq) {
 			raw_spin_unlock(&rq->lock);
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1153,7 +1153,15 @@ struct task_struct *pick_next_task_dl(st
 	dl_rq = &rq->dl;
 
 	if (need_pull_dl_task(rq, prev)) {
+		/*
+		 * This is OK, because current is on_cpu, which avoids it being
+		 * picked for load-balance and preemption/IRQs are still
+		 * disabled avoiding further scheduler activity on it and we're
+		 * being very careful to re-start the picking loop.
+		 */
+		lockdep_unpin_lock(&rq->lock);
 		pull_dl_task(rq);
+		lockdep_pin_lock(&rq->lock);
 		/*
 		 * pull_rt_task() can drop (and re-acquire) rq->lock; this
 		 * means a stop task can slip in, in which case we need to
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5392,7 +5392,15 @@ pick_next_task_fair(struct rq *rq, struc
 	return p;
 
 idle:
+	/*
+	 * This is OK, because current is on_cpu, which avoids it being picked
+	 * for load-balance and preemption/IRQs are still disabled avoiding
+	 * further scheduler activity on it and we're being very careful to
+	 * re-start the picking loop.
+	 */
+	lockdep_unpin_lock(&rq->lock);
 	new_tasks = idle_balance(rq);
+	lockdep_pin_lock(&rq->lock);
 	/*
 	 * Because idle_balance() releases (and re-acquires) rq->lock, it is
 	 * possible for any higher priority task to appear. In that case we
@@ -7426,9 +7434,6 @@ static int idle_balance(struct rq *this_
 		goto out;
 	}
 
-	/*
-	 * Drop the rq->lock, but keep IRQ/preempt disabled.
-	 */
 	raw_spin_unlock(&this_rq->lock);
 
 	update_blocked_averages(this_cpu);
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1478,7 +1478,15 @@ pick_next_task_rt(struct rq *rq, struct
 	struct rt_rq *rt_rq = &rq->rt;
 
 	if (need_pull_rt_task(rq, prev)) {
+		/*
+		 * This is OK, because current is on_cpu, which avoids it being
+		 * picked for load-balance and preemption/IRQs are still
+		 * disabled avoiding further scheduler activity on it and we're
+		 * being very careful to re-start the picking loop.
+		 */
+		lockdep_unpin_lock(&rq->lock);
 		pull_rt_task(rq);
+		lockdep_pin_lock(&rq->lock);
 		/*
 		 * pull_rt_task() can drop (and re-acquire) rq->lock; this
 		 * means a dl or stop task can slip in, in which case we need
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1438,8 +1438,10 @@ static inline struct rq *__task_rq_lock(
 	for (;;) {
 		rq = task_rq(p);
 		raw_spin_lock(&rq->lock);
-		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
+			lockdep_pin_lock(&rq->lock);
 			return rq;
+		}
 		raw_spin_unlock(&rq->lock);
 
 		while (unlikely(task_on_rq_migrating(p)))
@@ -1476,8 +1478,10 @@ static inline struct rq *task_rq_lock(st
 		 * If we observe the new cpu in task_rq_lock, the acquire will
 		 * pair with the WMB to ensure we must then also see migrating.
 		 */
-		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))
+		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p))) {
+			lockdep_pin_lock(&rq->lock);
 			return rq;
+		}
 		raw_spin_unlock(&rq->lock);
 		raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
 
@@ -1489,6 +1493,7 @@ static inline struct rq *task_rq_lock(st
 static inline void __task_rq_unlock(struct rq *rq)
 	__releases(rq->lock)
 {
+	lockdep_unpin_lock(&rq->lock);
 	raw_spin_unlock(&rq->lock);
 }
 
@@ -1497,6 +1502,7 @@ task_rq_unlock(struct rq *rq, struct tas
 	__releases(rq->lock)
 	__releases(p->pi_lock)
 {
+	lockdep_unpin_lock(&rq->lock);
 	raw_spin_unlock(&rq->lock);
 	raw_spin_unlock_irqrestore(&p->pi_lock, *flags);
 }


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