FAILED: patch "[PATCH] btrfs: fix missing error return in btrfs_drop_snapshot" failed to apply to 3.18-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 3.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From e19182c0fff451e3744c1107d98f072e7ca377a0 Mon Sep 17 00:00:00 2001
From: Jeff Mahoney <jeffm@suse.com>
Date: Mon, 4 Dec 2017 13:11:45 -0500
Subject: [PATCH] btrfs: fix missing error return in btrfs_drop_snapshot

If btrfs_del_root fails in btrfs_drop_snapshot, we'll pick up the
error but then return 0 anyway due to mixing err and ret.

Fixes: 79787eaab4612 ("btrfs: replace many BUG_ONs with proper error handling")
Cc: <stable@vger.kernel.org> # v3.4+
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 784d41e95ed9..16e46ee3cd16 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -9220,6 +9220,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
 	ret = btrfs_del_root(trans, fs_info, &root->root_key);
 	if (ret) {
 		btrfs_abort_transaction(trans, ret);
+		err = ret;
 		goto out_end_trans;
 	}