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dm: fix deadlock with request based dm and queue request_fn recursion 

Request based dm attempts to re-run the request queue off the
request completion path. If used with a driver that potentially does
end_io from its request_fn, we could deadlock trying to recurse
back into request dispatch. Fix this by punting the request queue
run to kblockd.

Tested to fix a quickly reproducible deadlock in such a scenario.

Cc: stable@kernel.org
Acked-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2012-11-06 12:24:26 +01:00
parent eac7cc52c6
commit a8c32a5c98
1 changed files with 7 additions and 1 deletions
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8
drivers/md/dm.c
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@ -740,8 +740,14 @@ static void rq_completed(struct mapped_device *md, int rw, int run_queue)
if (!md_in_flight(md))
wake_up(&md->wait);
/*
* Run this off this callpath, as drivers could invoke end_io while
* inside their request_fn (and holding the queue lock). Calling
* back into ->request_fn() could deadlock attempting to grab the
* queue lock again.
*/
if (run_queue)
blk_run_queue(md->queue);
blk_run_queue_async(md->queue);
/*
* dm_put() must be at the end of this function. See the comment above