From a035fc3e2531703b539f23bec4ca7943cfc69349 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Thu, 9 Dec 2010 16:17:51 +1100 Subject: [PATCH] md: fix possible deadlock in handling flush requests. As recorded in https://bugzilla.kernel.org/show_bug.cgi?id=24012 it is possible for a flush request through md to hang. This is due to an interaction between the recursion avoidance in generic_make_request, the insistence in md of only having one flush active at a time, and the possibility of dm (or md) submitting two flush requests to a device from the one generic_make_request. If a generic_make_request call into dm causes two flush requests to be queued (as happens if the dm table has two targets - they get one each), these two will be queued inside generic_make_request. Assume they are for the same md device. The first is processed and causes 1 or more flush requests to be sent to lower devices. These get queued within generic_make_request too. Then the second flush to the md device gets handled and it blocks waiting for the first flush to complete. But it won't complete until the two lower-device requests complete, and they haven't even been submitted yet as they are on the generic_make_request queue. The deadlock can be broken by using a separate thread to submit the requests to lower devices. md has such a thread readily available: md_wq. So use it to submit these requests. Reported-by: Giacomo Catenazzi Tested-by: Giacomo Catenazzi Signed-off-by: NeilBrown --- drivers/md/md.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/md/md.c b/drivers/md/md.c index 31f8e151d893..d66aaeddf95d 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -373,8 +373,9 @@ static void md_end_flush(struct bio *bio, int err) static void md_submit_flush_data(struct work_struct *ws); -static void submit_flushes(mddev_t *mddev) +static void submit_flushes(struct work_struct *ws) { + mddev_t *mddev = container_of(ws, mddev_t, flush_work); mdk_rdev_t *rdev; INIT_WORK(&mddev->flush_work, md_submit_flush_data); @@ -432,7 +433,8 @@ void md_flush_request(mddev_t *mddev, struct bio *bio) mddev->flush_bio = bio; spin_unlock_irq(&mddev->write_lock); - submit_flushes(mddev); + INIT_WORK(&mddev->flush_work, submit_flushes); + queue_work(md_wq, &mddev->flush_work); } EXPORT_SYMBOL(md_flush_request); -- GitLab