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Re: [dm-devel] [BUGFIX] [PATCH] freeze_bdev: don't deactivate successfully frozen MS_RDONLY sb



29.01.2010 02:56, Jun'ichi Nomura skrev:
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.


I've just verified that this patch works as intended on both 2.6.32 and 2.6.33-rc6, so for me it's still OK.

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

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 73d6a73..d11d028 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -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:
.



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