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block_dev: always serialize exclusive open attempts 

bd_prepare_to_claim() incorrectly allowed multiple attempts for
exclusive open to progress in parallel if the attempting holders are
identical.  This triggered BUG_ON() as reported in the following bug.

  https://bugzilla.kernel.org/show_bug.cgi?id=16393

__bd_abort_claiming() is used to finish claiming blocks and doesn't
work if multiple openers are inside a claiming block.  Allowing
multiple parallel open attempts to continue doesn't gain anything as
those are serialized down in the call chain anyway.  Fix it by always
allowing only single open attempt in a claiming block.

This problem can easily be reproduced by adding a delay after
bd_prepare_to_claim() and attempting to mount two partitions of a
disk.

stable: only applicable to v2.6.35

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo 2010-08-04 17:59:39 +02:00 committed by Linus Torvalds
parent d9b68e5e88
commit e75aa85892
1 changed files with 2 additions and 2 deletions
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4
fs/block_dev.c
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@ -681,8 +681,8 @@ retry:
if (!bd_may_claim(bdev, whole, holder))
return -EBUSY;
/* if someone else is claiming, wait for it to finish */
if (whole->bd_claiming && whole->bd_claiming != holder) {
/* if claiming is already in progress, wait for it to finish */
if (whole->bd_claiming) {
wait_queue_head_t *wq = bit_waitqueue(&whole->bd_claiming, 0);
DEFINE_WAIT(wait);