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freeze_bdev: don't deactivate successfully frozen MS_RDONLY sb

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Thanks Thomas and Christoph for testing and review.
I removed 'smp_wmb()' before up_write from the previous patch,
since up_write() should have necessary ordering constraints.
(I.e. the change of s_frozen is visible to others after up_write)
I'm quite sure the change is harmless but if you are uncomfortable
with Tested-by/Reviewed-by on the modified patch, please remove them.

If MS_RDONLY, freeze_bdev should just up_write(s_umount) instead of
deactivate_locked_super().
Also, keep sb->s_frozen consistent so that remount can check the frozen state.

Otherwise a crash reported here can happen:
http://lkml.org/lkml/2010/1/16/37
http://lkml.org/lkml/2010/1/28/53

This patch should be applied for 2.6.32 stable series, too.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Thomas Backlund <tmb@mandriva.org>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: stable@kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jun'ichi Nomura 2010-01-29 09:56:22 +09:00 committed by Al Viro
parent 8dd5ca532c
commit 4b06e5b9ad
1 changed files with 4 additions and 3 deletions
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7
fs/block_dev.c
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@ -246,7 +246,8 @@ struct super_block *freeze_bdev(struct block_device *bdev)
if (!sb)
goto out;
if (sb->s_flags & MS_RDONLY) {
deactivate_locked_super(sb);
sb->s_frozen = SB_FREEZE_TRANS;
up_write(&sb->s_umount);
mutex_unlock(&bdev->bd_fsfreeze_mutex);
return sb;
}
@ -307,7 +308,7 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
BUG_ON(sb->s_bdev != bdev);
down_write(&sb->s_umount);
if (sb->s_flags & MS_RDONLY)
goto out_deactivate;
goto out_unfrozen;
if (sb->s_op->unfreeze_fs) {
error = sb->s_op->unfreeze_fs(sb);
@ -321,11 +322,11 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
}
}
out_unfrozen:
sb->s_frozen = SB_UNFROZEN;
smp_wmb();
wake_up(&sb->s_wait_unfrozen);
out_deactivate:
if (sb)
deactivate_locked_super(sb);
out_unlock: