delayacct: Use raw_spinlocks

try_to_wake_up() might invoke delayacct_blkio_end() while holding the
pi_lock (which is a raw_spinlock_t). delayacct_blkio_end() acquires
task_delay_info.lock which is a spinlock_t. This causes a might sleep splat
on -RT where non raw spinlocks are converted to 'sleeping' spinlocks.

task_delay_info.lock is only held for a short amount of time so it's not a
problem latency wise to make convert it to a raw spinlock.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Balbir Singh <bsingharora@gmail.com>
Link: https://lkml.kernel.org/r/20180423161024.6710-1-bigeasy@linutronix.de

include/linux/delayacct.h

@@ -29,7 +29,7 @@
 
 #ifdef CONFIG_TASK_DELAY_ACCT
 struct task_delay_info {
-	spinlock_t	lock;
+	raw_spinlock_t	lock;
 	unsigned int	flags;	/* Private per-task flags */
 
 	/* For each stat XXX, add following, aligned appropriately

kernel/delayacct.c

@@ -44,23 +44,24 @@ void __delayacct_tsk_init(struct task_struct *tsk)
 {
 	tsk->delays = kmem_cache_zalloc(delayacct_cache, GFP_KERNEL);
 	if (tsk->delays)
-		spin_lock_init(&tsk->delays->lock);
+		raw_spin_lock_init(&tsk->delays->lock);
 }
 
 /*
  * Finish delay accounting for a statistic using its timestamps (@start),
  * accumalator (@total) and @count
  */
-static void delayacct_end(spinlock_t *lock, u64 *start, u64 *total, u32 *count)
+static void delayacct_end(raw_spinlock_t *lock, u64 *start, u64 *total,
+			  u32 *count)
 {
 	s64 ns = ktime_get_ns() - *start;
 	unsigned long flags;
 
 	if (ns > 0) {
-		spin_lock_irqsave(lock, flags);
+		raw_spin_lock_irqsave(lock, flags);
 		*total += ns;
 		(*count)++;
-		spin_unlock_irqrestore(lock, flags);
+		raw_spin_unlock_irqrestore(lock, flags);
 	}
 }
 
@@ -127,7 +128,7 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
 
 	/* zero XXX_total, non-zero XXX_count implies XXX stat overflowed */
 
-	spin_lock_irqsave(&tsk->delays->lock, flags);
+	raw_spin_lock_irqsave(&tsk->delays->lock, flags);
 	tmp = d->blkio_delay_total + tsk->delays->blkio_delay;
 	d->blkio_delay_total = (tmp < d->blkio_delay_total) ? 0 : tmp;
 	tmp = d->swapin_delay_total + tsk->delays->swapin_delay;
@@ -137,7 +138,7 @@ int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
 	d->blkio_count += tsk->delays->blkio_count;
 	d->swapin_count += tsk->delays->swapin_count;
 	d->freepages_count += tsk->delays->freepages_count;
-	spin_unlock_irqrestore(&tsk->delays->lock, flags);
+	raw_spin_unlock_irqrestore(&tsk->delays->lock, flags);
 
 	return 0;
 }
@@ -147,10 +148,10 @@ __u64 __delayacct_blkio_ticks(struct task_struct *tsk)
 	__u64 ret;
 	unsigned long flags;
 
-	spin_lock_irqsave(&tsk->delays->lock, flags);
+	raw_spin_lock_irqsave(&tsk->delays->lock, flags);
 	ret = nsec_to_clock_t(tsk->delays->blkio_delay +
 				tsk->delays->swapin_delay);
-	spin_unlock_irqrestore(&tsk->delays->lock, flags);
+	raw_spin_unlock_irqrestore(&tsk->delays->lock, flags);
 	return ret;
 }