dm: add memory barrier before waitqueue_active

Mikulas Patocka · snitm · commit 645efa84f6c7 · 2019-02-06T17:24:37.000-05:00
Block core changes to switch bio-based IO accounting to be percpu had a side-effect of altering DM core to now rely on calling waitqueue_active (in both bio-based and request-based) to check if another task is in dm_wait_for_completion(). A memory barrier is needed before calling waitqueue_active(). DM core doesn't piggyback on a preceding memory barrier so it must explicitly use its own. For more details on why using waitqueue_active() without a preceding barrier is unsafe, please see the comment before the waitqueue_active() definition in include/linux/wait.h. Add the missing memory barrier by switching to using wq_has_sleeper(). Fixes: 6f75723 ("dm: remove the pending IO accounting") Fixes: c4576ae ("dm: fix request-based dm's use of dm_wait_for_completion") Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
@@ -131,7 +131,7 @@ static void rq_end_stats(struct mapped_device *md, struct request *orig)
 static void rq_completed(struct mapped_device *md)
 {
 	/* nudge anyone waiting on suspend queue */
-	if (unlikely(waitqueue_active(&md->wait)))
+	if (unlikely(wq_has_sleeper(&md->wait)))
 		wake_up(&md->wait);
 
 	/*
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
@@ -699,7 +699,7 @@ static void end_io_acct(struct dm_io *io)
 				    true, duration, &io->stats_aux);
 
 	/* nudge anyone waiting on suspend queue */
-	if (unlikely(waitqueue_active(&md->wait)))
+	if (unlikely(wq_has_sleeper(&md->wait)))
 		wake_up(&md->wait);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -131,7 +131,7 @@ static void rq_end_stats(struct mapped_device md, struct request orig)`
`131`	`131`	`static void rq_completed(struct mapped_device *md)`
`132`	`132`	`{`
`133`	`133`	`/* nudge anyone waiting on suspend queue */`
`134`		`- if (unlikely(waitqueue_active(&md->wait)))`
	`134`	`+ if (unlikely(wq_has_sleeper(&md->wait)))`
`135`	`135`	`wake_up(&md->wait);`
`136`	`136`
`137`	`137`	`/*`
Original file line number	Diff line number	Diff line change
`@@ -699,7 +699,7 @@ static void end_io_acct(struct dm_io *io)`
`699`	`699`	`true, duration, &io->stats_aux);`
`700`	`700`
`701`	`701`	`/* nudge anyone waiting on suspend queue */`
`702`		`- if (unlikely(waitqueue_active(&md->wait)))`
	`702`	`+ if (unlikely(wq_has_sleeper(&md->wait)))`
`703`	`703`	`wake_up(&md->wait);`
`704`	`704`	`}`
`705`	`705`