bcachefs: Don't use bch2_btree_node_lock_write_nofail() in btree split path

It turns out - btree splits happen with the rest of the transaction
still locked, to avoid unnecessary restarts, which means using nofail
doesn't work here - we can deadlock.

Fortunately, we now have the ability to return errors here.

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

diff --git a/fs/bcachefs/btree_update_interior.c b/fs/bcachefs/btree_update_interior.c
index c4a5e83a56a436548263445e3b7a329644757cc7..29a5bc7d878984765bf417e61cc0a9c02f9220f0 100644 (file)
--- a/fs/bcachefs/btree_update_interior.c
+++ b/fs/bcachefs/btree_update_interior.c
@@ -1280,23 +1280,29 @@ static void bch2_btree_set_root_inmem(struct bch_fs *c, struct btree *b)
        bch2_recalc_btree_reserve(c);
 }
 
-static void bch2_btree_set_root(struct btree_update *as,
-                               struct btree_trans *trans,
-                               struct btree_path *path,
-                               struct btree *b)
+static int bch2_btree_set_root(struct btree_update *as,
+                              struct btree_trans *trans,
+                              struct btree_path *path,
+                              struct btree *b,
+                              bool nofail)
 {
        struct bch_fs *c = as->c;
-       struct btree *old;
 
        trace_and_count(c, btree_node_set_root, trans, b);
 
-       old = btree_node_root(c, b);
+       struct btree *old = btree_node_root(c, b);
 
        /*
         * Ensure no one is using the old root while we switch to the
         * new root:
         */
-       bch2_btree_node_lock_write_nofail(trans, path, &old->c);
+       if (nofail) {
+               bch2_btree_node_lock_write_nofail(trans, path, &old->c);
+       } else {
+               int ret = bch2_btree_node_lock_write(trans, path, &old->c);
+               if (ret)
+                       return ret;
+       }
 
        bch2_btree_set_root_inmem(c, b);
 
@@ -1310,6 +1316,7 @@ static void bch2_btree_set_root(struct btree_update *as,
         * depend on the new root would have to update the new root.
         */
        bch2_btree_node_unlock_write(trans, path, old);
+       return 0;
 }
 
 /* Interior node updates: */
@@ -1652,15 +1659,16 @@ static int btree_split(struct btree_update *as, struct btree_trans *trans,
        if (parent) {
                /* Split a non root node */
                ret = bch2_btree_insert_node(as, trans, path, parent, &as->parent_keys);
-               if (ret)
-                       goto err;
        } else if (n3) {
-               bch2_btree_set_root(as, trans, trans->paths + path, n3);
+               ret = bch2_btree_set_root(as, trans, trans->paths + path, n3, false);
        } else {
                /* Root filled up but didn't need to be split */
-               bch2_btree_set_root(as, trans, trans->paths + path, n1);
+               ret = bch2_btree_set_root(as, trans, trans->paths + path, n1, false);
        }
 
+       if (ret)
+               goto err;
+
        if (n3) {
                bch2_btree_update_get_open_buckets(as, n3);
                bch2_btree_node_write(c, n3, SIX_LOCK_intent, 0);
@@ -1863,7 +1871,9 @@ static void __btree_increase_depth(struct btree_update *as, struct btree_trans *
        bch2_keylist_add(&as->parent_keys, &b->key);
        btree_split_insert_keys(as, trans, path_idx, n, &as->parent_keys);
 
-       bch2_btree_set_root(as, trans, path, n);
+       int ret = bch2_btree_set_root(as, trans, path, n, true);
+       BUG_ON(ret);
+
        bch2_btree_update_get_open_buckets(as, n);
        bch2_btree_node_write(c, n, SIX_LOCK_intent, 0);
        bch2_trans_node_add(trans, path, n);
@@ -2106,12 +2116,13 @@ int bch2_btree_node_rewrite(struct btree_trans *trans,
        if (parent) {
                bch2_keylist_add(&as->parent_keys, &n->key);
                ret = bch2_btree_insert_node(as, trans, iter->path, parent, &as->parent_keys);
-               if (ret)
-                       goto err;
        } else {
-               bch2_btree_set_root(as, trans, btree_iter_path(trans, iter), n);
+               ret = bch2_btree_set_root(as, trans, btree_iter_path(trans, iter), n, false);
        }
 
+       if (ret)
+               goto err;
+
        bch2_btree_update_get_open_buckets(as, n);
        bch2_btree_node_write(c, n, SIX_LOCK_intent, 0);