dm: add memory barrier before waitqueue_active

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: 6f75723190d8 ("dm: remove the pending IO accounting")
Fixes: c4576aed8d85 ("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
index 4eb5f8c5653553a448d2b0971a3dca04ca0ffe4b..a20531e5f3b4c6936f75d0b647b8b05267a6ca03 100644 (file)
--- 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
index 2b53c3841b530b591c0c8ed688c0ea2b94b5f273..a0972a9301dec7557cde39a38bf2bfb19b1e145d 100644 (file)
--- 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);
 }