diff options
author | NeilBrown <neilb@suse.de> | 2010-12-09 16:17:51 +1100 |
---|---|---|
committer | NeilBrown <neilb@suse.de> | 2010-12-09 16:17:51 +1100 |
commit | a035fc3e2531703b539f23bec4ca7943cfc69349 (patch) | |
tree | f10e160ce65745fd7ac56838c491a45ae180cb1e | |
parent | a7a07e69653acf8540daa1da053cd84bf86e8e66 (diff) |
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 <cate@cateee.net>
Tested-by: Giacomo Catenazzi <cate@cateee.net>
Signed-off-by: NeilBrown <neilb@suse.de>
-rw-r--r-- | drivers/md/md.c | 6 |
1 files 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); |