bcachefs: bch2_btree_node_lock_write_nofail()

Taking a write lock will be able to fail, with the new cycle detector -
unless we pass it nofail, which is possible but not preferred.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_key_cache.c

@@ -342,11 +342,12 @@ static int btree_key_cache_fill(struct btree_trans *trans,
 		}
 	}
 
-	/*
-	 * XXX: not allowed to be holding read locks when we take a write lock,
-	 * currently
-	 */
-	bch2_btree_node_lock_write(trans, ck_path, ck_path->l[0].b);
+	ret = bch2_btree_node_lock_write(trans, ck_path, ck_path->l[0].b);
+	if (ret) {
+		kfree(new_k);
+		goto err;
+	}
+
 	if (new_k) {
 		kfree(ck->k);
 		ck->u64s = new_u64s;

fs/bcachefs/btree_locking.h

@@ -281,7 +281,7 @@ static inline int btree_node_lock(struct btree_trans *trans,
 
 void __bch2_btree_node_lock_write(struct btree_trans *, struct btree *);
 
-static inline void bch2_btree_node_lock_write(struct btree_trans *trans,
+static inline void bch2_btree_node_lock_write_nofail(struct btree_trans *trans,
 					      struct btree_path *path,
 					      struct btree *b)
 {
@@ -300,6 +300,15 @@ static inline void bch2_btree_node_lock_write(struct btree_trans *trans,
 		__bch2_btree_node_lock_write(trans, b);
 }
 
+static inline int __must_check
+bch2_btree_node_lock_write(struct btree_trans *trans,
+			   struct btree_path *path,
+			   struct btree *b)
+{
+	bch2_btree_node_lock_write_nofail(trans, path, b);
+	return 0;
+}
+
 /* relock: */
 
 bool bch2_btree_path_relock_norestart(struct btree_trans *,

fs/bcachefs/btree_update_interior.c

@@ -1163,7 +1163,7 @@ static void bch2_btree_set_root(struct btree_update *as,
 	 * Ensure no one is using the old root while we switch to the
 	 * new root:
 	 */
-	bch2_btree_node_lock_write(trans, path, old);
+	bch2_btree_node_lock_write_nofail(trans, path, old);
 
 	bch2_btree_set_root_inmem(c, b);
 
@@ -2002,7 +2002,7 @@ static int __bch2_btree_node_update_key(struct btree_trans *trans,
 	if (ret)
 		goto err;
 
-	bch2_btree_node_lock_write(trans, iter->path, b);
+	bch2_btree_node_lock_write_nofail(trans, iter->path, b);
 
 	if (new_hash) {
 		mutex_lock(&c->btree_cache.lock);

fs/bcachefs/btree_update_leaf.c

@@ -81,7 +81,7 @@ void bch2_btree_node_lock_for_insert(struct btree_trans *trans,
 				     struct btree_path *path,
 				     struct btree *b)
 {
-	bch2_btree_node_lock_write(trans, path, b);
+	bch2_btree_node_lock_write_nofail(trans, path, b);
 	bch2_btree_node_prep_for_write(trans, path, b);
 }