From: Josef Bacik <josef@toxicpanda.com>

commit 315bf8ef914f31d51d084af950703aa1e09a728c upstream.

While running my error injection script I hit a panic when we tried to
clean up the fs_root when freeing the fs_root.  This is because
fs_info->fs_root == PTR_ERR(-EIO), which isn't great.  Fix this by
setting fs_info->fs_root = NULL; if we fail to read the root.

CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Nikolay Borisov <redacted>
Reviewed-by: Johannes Thumshirn <redacted>
Reviewed-by: Qu Wenruo <redacted>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/btrfs/disk-io.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c

@@ -3200,6 +3200,7 @@ int __cold open_ctree(struct super_block
 	if (IS_ERR(fs_info->fs_root)) {
 		err = PTR_ERR(fs_info->fs_root);
 		btrfs_warn(fs_info, "failed to read fs tree: %d", err);
+		fs_info->fs_root = NULL;
 		goto fail_qgroup;
 	}