diff options
author | Shaohua Li <shli@fb.com> | 2017-02-28 13:00:20 -0800 |
---|---|---|
committer | Shaohua Li <shli@fb.com> | 2017-03-09 09:02:42 -0800 |
commit | 61eb2b43b99ebdc9bc6bc83d9792257b243e7cb3 (patch) | |
tree | 509d571e2f2cccce0beda5401a18c47e6505526b | |
parent | 1b3bae49fba52f1ec499c36c53bc07761a9f6c4d (diff) | |
download | linux-61eb2b43b99ebdc9bc6bc83d9792257b243e7cb3.tar.bz2 |
md/raid1/10: fix potential deadlock
Neil Brown pointed out a potential deadlock in raid 10 code with
bio_split/chain. The raid1 code could have the same issue, but recent
barrier rework makes it less likely to happen. The deadlock happens in
below sequence:
1. generic_make_request(bio), this will set current->bio_list
2. raid10_make_request will split bio to bio1 and bio2
3. __make_request(bio1), wait_barrer, add underlayer disk bio to
current->bio_list
4. __make_request(bio2), wait_barrer
If raise_barrier happens between 3 & 4, since wait_barrier runs at 3,
raise_barrier waits for IO completion from 3. And since raise_barrier
sets barrier, 4 waits for raise_barrier. But IO from 3 can't be
dispatched because raid10_make_request() doesn't finished yet.
The solution is to adjust the IO ordering. Quotes from Neil:
"
It is much safer to:
if (need to split) {
split = bio_split(bio, ...)
bio_chain(...)
make_request_fn(split);
generic_make_request(bio);
} else
make_request_fn(mddev, bio);
This way we first process the initial section of the bio (in 'split')
which will queue some requests to the underlying devices. These
requests will be queued in generic_make_request.
Then we queue the remainder of the bio, which will be added to the end
of the generic_make_request queue.
Then we return.
generic_make_request() will pop the lower-level device requests off the
queue and handle them first. Then it will process the remainder
of the original bio once the first section has been fully processed.
"
Note, this only happens in read path. In write path, the bio is flushed to
underlaying disks either by blk flush (from schedule) or offladed to raid1/10d.
It's queued in current->bio_list.
Cc: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org (v3.14+, only the raid10 part)
Suggested-by: NeilBrown <neilb@suse.com>
Reviewed-by: Jack Wang <jinpu.wang@profitbricks.com>
Signed-off-by: Shaohua Li <shli@fb.com>
-rw-r--r-- | drivers/md/raid1.c | 25 | ||||
-rw-r--r-- | drivers/md/raid10.c | 18 |
2 files changed, 41 insertions, 2 deletions
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index 10c3865e1186..c33e96e33b8e 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -1587,9 +1587,30 @@ static void raid1_make_request(struct mddev *mddev, struct bio *bio) split = bio; } - if (bio_data_dir(split) == READ) + if (bio_data_dir(split) == READ) { raid1_read_request(mddev, split); - else + + /* + * If a bio is splitted, the first part of bio will + * pass barrier but the bio is queued in + * current->bio_list (see generic_make_request). If + * there is a raise_barrier() called here, the second + * part of bio can't pass barrier. But since the first + * part bio isn't dispatched to underlaying disks yet, + * the barrier is never released, hence raise_barrier + * will alays wait. We have a deadlock. + * Note, this only happens in read path. For write + * path, the first part of bio is dispatched in a + * schedule() call (because of blk plug) or offloaded + * to raid10d. + * Quitting from the function immediately can change + * the bio order queued in bio_list and avoid the deadlock. + */ + if (split != bio) { + generic_make_request(bio); + break; + } + } else raid1_write_request(mddev, split); } while (split != bio); } diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index c4db6d1fb6a2..b1b1f982a722 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -1584,7 +1584,25 @@ static void raid10_make_request(struct mddev *mddev, struct bio *bio) split = bio; } + /* + * If a bio is splitted, the first part of bio will pass + * barrier but the bio is queued in current->bio_list (see + * generic_make_request). If there is a raise_barrier() called + * here, the second part of bio can't pass barrier. But since + * the first part bio isn't dispatched to underlaying disks + * yet, the barrier is never released, hence raise_barrier will + * alays wait. We have a deadlock. + * Note, this only happens in read path. For write path, the + * first part of bio is dispatched in a schedule() call + * (because of blk plug) or offloaded to raid10d. + * Quitting from the function immediately can change the bio + * order queued in bio_list and avoid the deadlock. + */ __make_request(mddev, split); + if (split != bio && bio_data_dir(bio) == READ) { + generic_make_request(bio); + break; + } } while (split != bio); /* In case raid10d snuck in to freeze_array */ |