[PATCH] direct-io: Use return from cmpxchg to decide of assignment happened

[Olof Johansson]

Not using the return value can in the generic case be racy, so it's better to
use the expected way of using that instead of comparing later.

This also resolved the warning caused on ARM and other architectures:

fs/direct-io.c: In function 'sb_init_dio_done_wq':
fs/direct-io.c:557:2: warning: value computed is not used [-Wunused-value]

Signed-off-by: Olof Johansson <olof@xxxxxxxxx>
---
 fs/direct-io.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 1782023..0e04142 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -544,6 +544,7 @@ static inline int dio_bio_reap(struct dio *dio, struct dio_submit *sdio)
  */
 static int sb_init_dio_done_wq(struct super_block *sb)
 {
+	struct workqueue_struct *old;
 	struct workqueue_struct *wq = alloc_workqueue("dio/%s",
 						      WQ_MEM_RECLAIM, 0,
 						      sb->s_id);
@@ -552,9 +553,9 @@ static int sb_init_dio_done_wq(struct super_block *sb)
 	/*
 	 * This has to be atomic as more DIOs can race to create the workqueue
 	 */
-	cmpxchg(&sb->s_dio_done_wq, NULL, wq);
+	old = cmpxchg(&sb->s_dio_done_wq, NULL, wq);
 	/* Someone created workqueue before us? Free ours... */
-	if (wq != sb->s_dio_done_wq)
+	if (old)
 		destroy_workqueue(wq);
 	return 0;
 }
-- 
1.7.10.4

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