bcachefs: bch2_gc_btree() should not use btree_root_lock

btree_root_lock is for the root keys in btree_root, not the pointers to
the nodes themselves; this fixes a lock ordering issue between
btree_root_lock and btree node locks.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/btree_gc.c b/fs/bcachefs/btree_gc.c
index 7c72a9e..a0deb82 100644 (file)
--- a/fs/bcachefs/btree_gc.c
+++ b/fs/bcachefs/btree_gc.c
@@ -641,16 +641,30 @@ static int bch2_gc_btree(struct btree_trans *trans, enum btree_id btree, bool in
                target_depth = 0;
 
        /* root */
-       mutex_lock(&c->btree_root_lock);
-       struct btree *b = bch2_btree_id_root(c, btree)->b;
-       if (!btree_node_fake(b)) {
+       do {
+retry_root:
+               bch2_trans_begin(trans);
+
+               struct btree_iter iter;
+               bch2_trans_node_iter_init(trans, &iter, btree, POS_MIN,
+                                         0, bch2_btree_id_root(c, btree)->b->c.level, 0);
+               struct btree *b = bch2_btree_iter_peek_node(&iter);
+               ret = PTR_ERR_OR_ZERO(b);
+               if (ret)
+                       goto err_root;
+
+               if (b != btree_node_root(c, b)) {
+                       bch2_trans_iter_exit(trans, &iter);
+                       goto retry_root;
+               }
+
                gc_pos_set(c, gc_pos_btree(btree, b->c.level + 1, SPOS_MAX));
-               ret = lockrestart_do(trans,
-                       bch2_gc_mark_key(trans, b->c.btree_id, b->c.level + 1,
-                                        NULL, NULL, bkey_i_to_s_c(&b->key), initial));
+               struct bkey_s_c k = bkey_i_to_s_c(&b->key);
+               ret = bch2_gc_mark_key(trans, btree, b->c.level + 1, NULL, NULL, k, initial);
                level = b->c.level;
-       }
-       mutex_unlock(&c->btree_root_lock);
+err_root:
+               bch2_trans_iter_exit(trans, &iter);
+       } while (bch2_err_matches(ret, BCH_ERR_transaction_restart));
 
        if (ret)
                return ret;