[Devel] [PATCH rh7 1/4] fs: do not fail on double freeze bdev w/o sb

[Vladimir Davydov]

It's possible to freeze a bdev which is not mounted. In this case
freeze_bdev() only increments bd_fsfrozen_count in order to prevent the
bdev from being mounted and does nothing else. A second freeze attempt
on the same device is supposed to increment bd_fsfrozen_count again, but
it results in NULL ptr dereference, because freeze_bdev() doesn't check
the return value of get_super(). Fix that.

Signed-off-by: Vladimir Davydov <vdavydov at virtuozzo.com>
---
 fs/block_dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 4575c62d8b0b..325ee7161fbf 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -227,7 +227,8 @@ struct super_block *freeze_bdev(struct block_device *bdev)
 		 * thaw_bdev drops it.
 		 */
 		sb = get_super(bdev);
-		drop_super(sb);
+		if (sb)
+			drop_super(sb);
 		mutex_unlock(&bdev->bd_fsfreeze_mutex);
 		return sb;
 	}
-- 
2.1.4