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| author | Tejun Heo <tj@kernel.org> | 2014-06-18 11:21:08 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2014-07-01 10:27:06 -0600 |
| commit | 531ed6261e7466907418b1a9971a5c71d7d250e4 (patch) | |
| tree | c4620c6c04575eb0d3fa2d24eb418a8dd8859a1e /block/blk-mq.c | |
| parent | 17737d3b5997ac9f810967f0c6014d124ec39490 (diff) | |
| download | lwn-531ed6261e7466907418b1a9971a5c71d7d250e4.tar.gz lwn-531ed6261e7466907418b1a9971a5c71d7d250e4.zip | |
blk-mq: fix a memory ordering bug in blk_mq_queue_enter()
blk-mq uses a percpu_counter to keep track of how many usages are in
flight. The percpu_counter is drained while freezing to ensure that
no usage is left in-flight after freezing is complete.
blk_mq_queue_enter/exit() and blk_mq_[un]freeze_queue() implement this
per-cpu gating mechanism; unfortunately, it contains a subtle bug -
smp_wmb() in blk_mq_queue_enter() doesn't prevent prevent the cpu from
fetching @q->bypass_depth before incrementing @q->mq_usage_counter and
if freezing happens inbetween the caller can slip through and freezing
can be complete while there are active users.
Use smp_mb() instead so that bypass_depth and mq_usage_counter
modifications and tests are properly interlocked.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Nicholas A. Bellinger <nab@linux-iscsi.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-mq.c')
| -rw-r--r-- | block/blk-mq.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/block/blk-mq.c b/block/blk-mq.c index ad69ef657e85..9541f5111ba6 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -81,7 +81,7 @@ static int blk_mq_queue_enter(struct request_queue *q) int ret; __percpu_counter_add(&q->mq_usage_counter, 1, 1000000); - smp_wmb(); + smp_mb(); /* we have problems freezing the queue if it's initializing */ if (!blk_queue_dying(q) && |