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author | Lukas Czerner <lczerner@redhat.com> | 2011-03-11 12:23:53 +0300 |
---|---|---|
committer | Jens Axboe <jaxboe@fusionio.com> | 2011-03-11 17:36:08 +0300 |
commit | 0aeea18964173715a1037034ef6838198f319319 (patch) | |
tree | 62ff402a41a675f0269bf5172d14b7db8c4e47ee /block/blk-lib.c | |
parent | 9179746652faf0aba07b8b7f770dcf29892a24c6 (diff) | |
download | linux-0aeea18964173715a1037034ef6838198f319319.tar.xz |
block: fix mis-synchronisation in blkdev_issue_zeroout()
BZ29402
https://bugzilla.kernel.org/show_bug.cgi?id=29402
We can hit serious mis-synchronization in bio completion path of
blkdev_issue_zeroout() leading to a panic.
The problem is that when we are going to wait_for_completion() in
blkdev_issue_zeroout() we check if the bb.done equals issued (number of
submitted bios). If it does, we can skip the wait_for_completition()
and just out of the function since there is nothing to wait for.
However, there is a ordering problem because bio_batch_end_io() is
calling atomic_inc(&bb->done) before complete(), hence it might seem to
blkdev_issue_zeroout() that all bios has been completed and exit. At
this point when bio_batch_end_io() is going to call complete(bb->wait),
bb and wait does not longer exist since it was allocated on stack in
blkdev_issue_zeroout() ==> panic!
(thread 1) (thread 2)
bio_batch_end_io() blkdev_issue_zeroout()
if(bb) { ...
if (bb->end_io) ...
bb->end_io(bio, err); ...
atomic_inc(&bb->done); ...
... while (issued != atomic_read(&bb.done))
... (let issued == bb.done)
... (do the rest of the function)
... return ret;
complete(bb->wait);
^^^^^^^^
panic
We can fix this easily by simplifying bio_batch and completion counting.
Also remove bio_end_io_t *end_io since it is not used.
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reported-by: Eric Whitney <eric.whitney@hp.com>
Tested-by: Eric Whitney <eric.whitney@hp.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
CC: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Diffstat (limited to 'block/blk-lib.c')
-rw-r--r-- | block/blk-lib.c | 19 |
1 files changed, 7 insertions, 12 deletions
diff --git a/block/blk-lib.c b/block/blk-lib.c index eec78becb355..bd3e8df4d5e2 100644 --- a/block/blk-lib.c +++ b/block/blk-lib.c @@ -109,7 +109,6 @@ struct bio_batch atomic_t done; unsigned long flags; struct completion *wait; - bio_end_io_t *end_io; }; static void bio_batch_end_io(struct bio *bio, int err) @@ -122,12 +121,9 @@ static void bio_batch_end_io(struct bio *bio, int err) else clear_bit(BIO_UPTODATE, &bb->flags); } - if (bb) { - if (bb->end_io) - bb->end_io(bio, err); - atomic_inc(&bb->done); - complete(bb->wait); - } + if (bb) + if (atomic_dec_and_test(&bb->done)) + complete(bb->wait); bio_put(bio); } @@ -150,13 +146,12 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector, int ret; struct bio *bio; struct bio_batch bb; - unsigned int sz, issued = 0; + unsigned int sz; DECLARE_COMPLETION_ONSTACK(wait); - atomic_set(&bb.done, 0); + atomic_set(&bb.done, 1); bb.flags = 1 << BIO_UPTODATE; bb.wait = &wait; - bb.end_io = NULL; submit: ret = 0; @@ -185,12 +180,12 @@ submit: break; } ret = 0; - issued++; + atomic_inc(&bb.done); submit_bio(WRITE, bio); } /* Wait for bios in-flight */ - while (issued != atomic_read(&bb.done)) + if (!atomic_dec_and_test(&bb.done)) wait_for_completion(&wait); if (!test_bit(BIO_UPTODATE, &bb.flags)) |