btrfs: backref, only search backref entries from leaves of the same root

BugLink: https://bugs.launchpad.net/bugs/1916061

commit cfc0eed upstream.

We could have some nodes/leaves in subvolume whose owner are not the
that subvolume. In this way, when we resolve normal backrefs of that
subvolume, we should avoid collecting those references from these blocks.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: ethanwu <ethanwu@synology.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

Author: ethanwu-syno

fs/btrfs/backref.c

@@ -443,11 +443,14 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
 	 *    slot == nritems.
 	 * 2. We are searching for normal backref but bytenr of this leaf
 	 *    matches shared data backref
+	 * 3. The leaf owner is not equal to the root we are searching
+	 *
 	 * For these cases, go to the next leaf before we continue.
 	 */
 	eb = path->nodes[0];
 	if (path->slots[0] >= btrfs_header_nritems(eb) ||
-	    is_shared_data_backref(preftrees, eb->start)) {
+	    is_shared_data_backref(preftrees, eb->start) ||
+	    ref->root_id != btrfs_header_owner(eb)) {
 		if (time_seq == SEQ_LAST)
 			ret = btrfs_next_leaf(root, path);
 		else
@@ -466,9 +469,12 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path,
 
 		/*
 		 * We are searching for normal backref but bytenr of this leaf
-		 * matches shared data backref.
+		 * matches shared data backref, OR
+		 * the leaf owner is not equal to the root we are searching for
 		 */
-		if (slot == 0 && is_shared_data_backref(preftrees, eb->start)) {
+		if (slot == 0 &&
+		    (is_shared_data_backref(preftrees, eb->start) ||
+		     ref->root_id != btrfs_header_owner(eb))) {
 			if (time_seq == SEQ_LAST)
 				ret = btrfs_next_leaf(root, path);
 			else