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authorJens Axboe <axboe@fb.com>2014-09-16 10:37:37 -0600
committerJens Axboe <axboe@fb.com>2014-09-22 11:54:04 -0600
commit538b75341835e3c2041ff066408de10d24fdc830 (patch)
tree6b7b60f296779302cc70d7c79e47b4dcc440a9be
parent37504a3be90b69438426d74ccf467a9fe192932b (diff)
downloadlinux-538b75341835e3c2041ff066408de10d24fdc830.tar.bz2
blk-mq: request deadline must be visible before marking rq as started
When we start the request, we set the deadline and flip the bits marking the request as started and non-complete. However, it's important that the deadline store is ordered before flipping the bits, otherwise we could have a small window where the request is marked started but with an invalid deadline. This can confuse the timeout handling. Suggested-by: Ming Lei <tom.leiming@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
-rw-r--r--block/blk-mq.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 383ea0cb1f0a..a13c40ca8230 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -393,6 +393,12 @@ static void blk_mq_start_request(struct request *rq, bool last)
blk_add_timer(rq);
/*
+ * Ensure that ->deadline is visible before set the started
+ * flag and clear the completed flag.
+ */
+ smp_mb__before_atomic();
+
+ /*
* Mark us as started and clear complete. Complete might have been
* set if requeue raced with timeout, which then marked it as
* complete. So be sure to clear complete again when we start