[PATCH 1/5] fsfreeze: Prevent emergency thaw from looping infinitely

[Dave Chinner <david@fromorbit.com>]

From: Dave Chinner <dchinner@redhat.com>

The thawing of a filesystem through sysrq-j loops infinitely as it
incorrectly detects a thawed filesytsem as frozen and tries to
unfreeze repeatedly. This is a regression caused by
4504230a71566785a05d3e6b53fa1ee071b864eb ("freeze_bdev: grab active
reference to frozen superblocks") in that it no longer returned
-EINVAL for superblocks that were not frozen.

Return -EINVAL when the filesystem is already unfrozen to avoid this
problem.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/block_dev.c |   13 +++++--------
 1 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7346c96..366ac38 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -276,22 +276,19 @@ int thaw_bdev(struct block_device *bdev, struct super_block *sb)
 	if (!bdev->bd_fsfreeze_count)
 		goto out;
 
-	error = 0;
-	if (--bdev->bd_fsfreeze_count > 0)
+	if (!sb)
 		goto out;
 
-	if (!sb)
+	error = 0;
+	if (--bdev->bd_fsfreeze_count > 0)
 		goto out;
 
 	error = thaw_super(sb);
-	if (error) {
+	if (error)
 		bdev->bd_fsfreeze_count++;
-		mutex_unlock(&bdev->bd_fsfreeze_mutex);
-		return error;
-	}
 out:
 	mutex_unlock(&bdev->bd_fsfreeze_mutex);
-	return 0;
+	return error;
 }
 EXPORT_SYMBOL(thaw_bdev);
 
-- 
1.7.1