From patchwork Mon Dec 10 14:20:07 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [3.5.y.z, extended, stable] Patch "dm: fix deadlock with request based dm and queue request_fn" has been added to staging queue Date: Mon, 10 Dec 2012 04:20:07 -0000 From: Herton Ronaldo Krzesinski X-Patchwork-Id: 204920 Message-Id: <1355149207-9485-1-git-send-email-herton.krzesinski@canonical.com> To: Jens Axboe Cc: kernel-team@lists.ubuntu.com, Alasdair G Kergon This is a note to let you know that I have just added a patch titled dm: fix deadlock with request based dm and queue request_fn to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Herton ------ >From fdcb10668dc4539e4c38afbcb4714d542e3c5401 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 6 Nov 2012 12:24:26 +0100 Subject: [PATCH] dm: fix deadlock with request based dm and queue request_fn recursion commit a8c32a5c98943d370ea606a2e7dc04717eb92206 upstream. 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. Acked-by: Alasdair G Kergon Signed-off-by: Jens Axboe Signed-off-by: Herton Ronaldo Krzesinski --- drivers/md/dm.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) -- 1.7.9.5 diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 9ff3019..32370ea 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -754,8 +754,14 @@ 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