Commit 4b06e5b9 authored Jan 29, 2010 by Jun'ichi Nomura Committed by Al Viro Feb 07, 2010

freeze_bdev: don't deactivate successfully frozen MS_RDONLY sb

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>

parent 8dd5ca53

fs/block_dev.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -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: