Btrfs: fix for patch "cleanup: don't check the same thing twice"

Mitch Harder noticed that the patch 3c64a1a mentioned in the subject
line was causing a kernel BUG() on snapshot deletion.

The patch was wrong. It did not handle cached roots correctly. The
check for root_refs == 0 was removed everywhere where
btrfs_read_fs_root_no_name() had been used to retrieve the root,
because this check was already dealt with in
btrfs_read_fs_root_no_name(). But in the case when the root was
found in the cache, there was no such check.

This patch adds the missing check in the case where the root is
found in the cache.

Reported-by: Mitch Harder <mitch.harder@sabayonlinux.org>
Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 0f75a01f69e2e3e39f791696b7289f25e8e87b54..21d1d066758ea94ac2ffc7a4d3dff0fe88b128cc 100644 (file)
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1584,8 +1584,11 @@ struct btrfs_root *btrfs_read_fs_root_no_name(struct btrfs_fs_info *fs_info,
                                            ERR_PTR(-ENOENT);
 again:
        root = btrfs_lookup_fs_root(fs_info, location->objectid);
-       if (root)
+       if (root) {
+               if (btrfs_root_refs(&root->root_item) == 0)
+                       return ERR_PTR(-ENOENT);
                return root;
+       }
 
        root = btrfs_read_fs_root(fs_info->tree_root, location);
        if (IS_ERR(root))