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

Pull scheduler fix from Ingo Molnar:
 "A delayacct statistics correctness fix"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  delayacct: Account blkio completion on the correct task

2 files changed, 29 insertions, 19 deletions

diff --git a/kernel/delayacct.c b/kernel/delayacct.c
index 4a1c33416b6a..e2764d767f18 100644
--- a/kernel/delayacct.c
+++ b/kernel/delayacct.c
@@ -51,16 +51,16 @@ void __delayacct_tsk_init(struct task_struct *tsk)
  * Finish delay accounting for a statistic using its timestamps (@start),
  * accumalator (@total) and @count
  */
-static void delayacct_end(u64 *start, u64 *total, u32 *count)
+static void delayacct_end(spinlock_t *lock, u64 *start, u64 *total, u32 *count)
 {
 	s64 ns = ktime_get_ns() - *start;
 	unsigned long flags;
 
 	if (ns > 0) {
-		spin_lock_irqsave(&current->delays->lock, flags);
+		spin_lock_irqsave(lock, flags);
 		*total += ns;
 		(*count)++;
-		spin_unlock_irqrestore(&current->delays->lock, flags);
+		spin_unlock_irqrestore(lock, flags);
 	}
 }
 
@@ -69,17 +69,25 @@ void __delayacct_blkio_start(void)
 	current->delays->blkio_start = ktime_get_ns();
 }
 
-void __delayacct_blkio_end(void)
+/*
+ * We cannot rely on the `current` macro, as we haven't yet switched back to
+ * the process being woken.
+ */
+void __delayacct_blkio_end(struct task_struct *p)
 {
-	if (current->delays->flags & DELAYACCT_PF_SWAPIN)
-		/* Swapin block I/O */
-		delayacct_end(&current->delays->blkio_start,
-			&current->delays->swapin_delay,
-			&current->delays->swapin_count);
-	else	/* Other block I/O */
-		delayacct_end(&current->delays->blkio_start,
-			&current->delays->blkio_delay,
-			&current->delays->blkio_count);
+	struct task_delay_info *delays = p->delays;
+	u64 *total;
+	u32 *count;
+
+	if (p->delays->flags & DELAYACCT_PF_SWAPIN) {
+		total = &delays->swapin_delay;
+		count = &delays->swapin_count;
+	} else {
+		total = &delays->blkio_delay;
+		count = &delays->blkio_count;
+	}
+
+	delayacct_end(&delays->lock, &delays->blkio_start, total, count);
 }
 
 int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
@@ -153,8 +161,10 @@ void __delayacct_freepages_start(void)
 
 void __delayacct_freepages_end(void)
 {
-	delayacct_end(&current->delays->freepages_start,
-			&current->delays->freepages_delay,
-			&current->delays->freepages_count);
+	delayacct_end(
+		&current->delays->lock,
+		&current->delays->freepages_start,
+		&current->delays->freepages_delay,
+		&current->delays->freepages_count);
 }
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 644fa2e3d993..a7bf32aabfda 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2056,7 +2056,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 	p->state = TASK_WAKING;
 
 	if (p->in_iowait) {
-		delayacct_blkio_end();
+		delayacct_blkio_end(p);
 		atomic_dec(&task_rq(p)->nr_iowait);
 	}
 
@@ -2069,7 +2069,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags)
 #else /* CONFIG_SMP */
 
 	if (p->in_iowait) {
-		delayacct_blkio_end();
+		delayacct_blkio_end(p);
 		atomic_dec(&task_rq(p)->nr_iowait);
 	}
 
@@ -2122,7 +2122,7 @@ static void try_to_wake_up_local(struct task_struct *p, struct rq_flags *rf)
 
 	if (!task_on_rq_queued(p)) {
 		if (p->in_iowait) {
-			delayacct_blkio_end();
+			delayacct_blkio_end(p);
 			atomic_dec(&rq->nr_iowait);
 		}
 		ttwu_activate(rq, p, ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK);