3 files changed, 114 insertions, 41 deletions

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index b3268f4ea5f3..771a036867dc 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -544,7 +544,18 @@ static int resolve_indirect_ref(struct btrfs_fs_info *fs_info,
 	int level = ref->level;
 	struct btrfs_key search_key = ref->key_for_search;
 
-	root = btrfs_get_fs_root(fs_info, ref->root_id, false);
+	/*
+	 * If we're search_commit_root we could possibly be holding locks on
+	 * other tree nodes.  This happens when qgroups does backref walks when
+	 * adding new delayed refs.  To deal with this we need to look in cache
+	 * for the root, and if we don't find it then we need to search the
+	 * tree_root's commit root, thus the btrfs_get_fs_root_commit_root usage
+	 * here.
+	 */
+	if (path->search_commit_root)
+		root = btrfs_get_fs_root_commit_root(fs_info, path, ref->root_id);
+	else
+		root = btrfs_get_fs_root(fs_info, ref->root_id, false);
 	if (IS_ERR(root)) {
 		ret = PTR_ERR(root);
 		goto out_free;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 764001609a15..278001a49d2e 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1281,32 +1281,26 @@ int btrfs_add_log_tree(struct btrfs_trans_handle *trans,
 	return 0;
 }
 
-struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
-					struct btrfs_key *key)
+static struct btrfs_root *read_tree_root_path(struct btrfs_root *tree_root,
+					      struct btrfs_path *path,
+					      struct btrfs_key *key)
 {
 	struct btrfs_root *root;
 	struct btrfs_fs_info *fs_info = tree_root->fs_info;
-	struct btrfs_path *path;
 	u64 generation;
 	int ret;
 	int level;
 
-	path = btrfs_alloc_path();
-	if (!path)
-		return ERR_PTR(-ENOMEM);
-
 	root = btrfs_alloc_root(fs_info, key->objectid, GFP_NOFS);
-	if (!root) {
-		ret = -ENOMEM;
-		goto alloc_fail;
-	}
+	if (!root)
+		return ERR_PTR(-ENOMEM);
 
 	ret = btrfs_find_root(tree_root, key, path,
 			      &root->root_item, &root->root_key);
 	if (ret) {
 		if (ret > 0)
 			ret = -ENOENT;
-		goto find_fail;
+		goto fail;
 	}
 
 	generation = btrfs_root_generation(&root->root_item);
@@ -1317,21 +1311,31 @@ struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
 	if (IS_ERR(root->node)) {
 		ret = PTR_ERR(root->node);
 		root->node = NULL;
-		goto find_fail;
+		goto fail;
 	} else if (!btrfs_buffer_uptodate(root->node, generation, 0)) {
 		ret = -EIO;
-		goto find_fail;
+		goto fail;
 	}
 	root->commit_root = btrfs_root_node(root);
-out:
-	btrfs_free_path(path);
 	return root;
-
-find_fail:
+fail:
 	btrfs_put_root(root);
-alloc_fail:
-	root = ERR_PTR(ret);
-	goto out;
+	return ERR_PTR(ret);
+}
+
+struct btrfs_root *btrfs_read_tree_root(struct btrfs_root *tree_root,
+					struct btrfs_key *key)
+{
+	struct btrfs_root *root;
+	struct btrfs_path *path;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return ERR_PTR(-ENOMEM);
+	root = read_tree_root_path(tree_root, path, key);
+	btrfs_free_path(path);
+
+	return root;
 }
 
 /*
@@ -1419,6 +1423,31 @@ static struct btrfs_root *btrfs_lookup_fs_root(struct btrfs_fs_info *fs_info,
 	return root;
 }
 
+static struct btrfs_root *btrfs_get_global_root(struct btrfs_fs_info *fs_info,
+						u64 objectid)
+{
+	if (objectid == BTRFS_ROOT_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->tree_root);
+	if (objectid == BTRFS_EXTENT_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->extent_root);
+	if (objectid == BTRFS_CHUNK_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->chunk_root);
+	if (objectid == BTRFS_DEV_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->dev_root);
+	if (objectid == BTRFS_CSUM_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->csum_root);
+	if (objectid == BTRFS_QUOTA_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->quota_root) ?
+			fs_info->quota_root : ERR_PTR(-ENOENT);
+	if (objectid == BTRFS_UUID_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->uuid_root) ?
+			fs_info->uuid_root : ERR_PTR(-ENOENT);
+	if (objectid == BTRFS_FREE_SPACE_TREE_OBJECTID)
+		return btrfs_grab_root(fs_info->free_space_root) ?
+			fs_info->free_space_root : ERR_PTR(-ENOENT);
+	return NULL;
+}
+
 int btrfs_insert_fs_root(struct btrfs_fs_info *fs_info,
 			 struct btrfs_root *root)
 {
@@ -1518,25 +1547,9 @@ static struct btrfs_root *btrfs_get_root_ref(struct btrfs_fs_info *fs_info,
 	struct btrfs_key key;
 	int ret;
 
-	if (objectid == BTRFS_ROOT_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->tree_root);
-	if (objectid == BTRFS_EXTENT_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->extent_root);
-	if (objectid == BTRFS_CHUNK_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->chunk_root);
-	if (objectid == BTRFS_DEV_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->dev_root);
-	if (objectid == BTRFS_CSUM_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->csum_root);
-	if (objectid == BTRFS_QUOTA_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->quota_root) ?
-			fs_info->quota_root : ERR_PTR(-ENOENT);
-	if (objectid == BTRFS_UUID_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->uuid_root) ?
-			fs_info->uuid_root : ERR_PTR(-ENOENT);
-	if (objectid == BTRFS_FREE_SPACE_TREE_OBJECTID)
-		return btrfs_grab_root(fs_info->free_space_root) ?
-			fs_info->free_space_root : ERR_PTR(-ENOENT);
+	root = btrfs_get_global_root(fs_info, objectid);
+	if (root)
+		return root;
 again:
 	root = btrfs_lookup_fs_root(fs_info, objectid);
 	if (root) {
@@ -1622,6 +1635,52 @@ struct btrfs_root *btrfs_get_new_fs_root(struct btrfs_fs_info *fs_info,
 }
 
 /*
+ * btrfs_get_fs_root_commit_root - return a root for the given objectid
+ * @fs_info:	the fs_info
+ * @objectid:	the objectid we need to lookup
+ *
+ * This is exclusively used for backref walking, and exists specifically because
+ * of how qgroups does lookups.  Qgroups will do a backref lookup at delayed ref
+ * creation time, which means we may have to read the tree_root in order to look
+ * up a fs root that is not in memory.  If the root is not in memory we will
+ * read the tree root commit root and look up the fs root from there.  This is a
+ * temporary root, it will not be inserted into the radix tree as it doesn't
+ * have the most uptodate information, it'll simply be discarded once the
+ * backref code is finished using the root.
+ */
+struct btrfs_root *btrfs_get_fs_root_commit_root(struct btrfs_fs_info *fs_info,
+						 struct btrfs_path *path,
+						 u64 objectid)
+{
+	struct btrfs_root *root;
+	struct btrfs_key key;
+
+	ASSERT(path->search_commit_root && path->skip_locking);
+
+	/*
+	 * This can return -ENOENT if we ask for a root that doesn't exist, but
+	 * since this is called via the backref walking code we won't be looking
+	 * up a root that doesn't exist, unless there's corruption.  So if root
+	 * != NULL just return it.
+	 */
+	root = btrfs_get_global_root(fs_info, objectid);
+	if (root)
+		return root;
+
+	root = btrfs_lookup_fs_root(fs_info, objectid);
+	if (root)
+		return root;
+
+	key.objectid = objectid;
+	key.type = BTRFS_ROOT_ITEM_KEY;
+	key.offset = (u64)-1;
+	root = read_tree_root_path(fs_info->tree_root, path, &key);
+	btrfs_release_path(path);
+
+	return root;
+}
+
+/*
  * called by the kthread helper functions to finally call the bio end_io
  * functions.  This is where read checksum verification actually happens
  */
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index fee69ced58b4..182540bdcea0 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -69,6 +69,9 @@ struct btrfs_root *btrfs_get_fs_root(struct btrfs_fs_info *fs_info,
 				     u64 objectid, bool check_ref);
 struct btrfs_root *btrfs_get_new_fs_root(struct btrfs_fs_info *fs_info,
 					 u64 objectid, dev_t anon_dev);
+struct btrfs_root *btrfs_get_fs_root_commit_root(struct btrfs_fs_info *fs_info,
+						 struct btrfs_path *path,
+						 u64 objectid);
 
 void btrfs_free_fs_info(struct btrfs_fs_info *fs_info);
 int btrfs_cleanup_fs_roots(struct btrfs_fs_info *fs_info);