Currently if a mounted-btrfs instance is mounted for the 2nd time
without first unmounting the first instance then we hit a memory leak
in btrfs_mount_root due to the fs_info of the acquired superblock is
different than the newly allocated fs info. Fix this by specifically
checking if the fs_info instance of the newly acquired superblock is
the same as ours and free it if not.

Reproducer:

mount /dev/vdc /media/scratch
mount /dev/vdc /media/scratch2 <- memory leak hit

Signed-off-by: Nikolay Borisov <nbori...@suse.com>
---
 fs/btrfs/super.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e57eb6e70278..ea3bca85be44 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1612,7 +1612,11 @@ static struct dentry *btrfs_mount_root(struct 
file_system_type *fs_type,
                goto error_sec_opts;
        }
 
-       fs_info = btrfs_sb(s);
+       if (btrfs_sb(s) != fs_info) {
+               free_fs_info(fs_info);
+               fs_info = btrfs_sb(s);
+       }
+
        error = setup_security_options(fs_info, s, &new_sec_opts);
        if (error) {
                deactivate_locked_super(s);
-- 
2.7.4

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