From: Kent Overstreet Date: Sat, 10 May 2025 18:42:37 +0000 (-0400) Subject: bcachefs: Fix broken btree_path lock invariants in next_node() X-Git-Tag: v6.15-rc7~22^2~7 X-Git-Url: http://git.ipfire.org/gitweb/gitweb.cgi?a=commitdiff_plain;h=b1c71cb492bb26dc883b11b5bd085d2467508f84;p=thirdparty%2Flinux.git bcachefs: Fix broken btree_path lock invariants in next_node() This fixes btree locking assert pops users were seeing during evacuate: https://github.com/koverstreet/bcachefs/issues/878 May 09 22:45:02 sharon kernel: bcachefs (68116e25-fa2d-4c6f-86c7-e8b431d792ae): bch2_btree_insert_node(): node not locked at level 1 May 09 22:45:02 sharon kernel: bch2_btree_node_rewrite [bcachefs]: watermark=btree no_check_rw alloc l=0-1 mode=none nodes_written=0 cl.remaining=2 journal_seq=0 May 09 22:45:02 sharon kernel: path: idx 1 ref 1:0 S B btree=alloc level=0 pos 0:3699637:0 0:3698012:1-0:3699637:0 bch2_move_btree.isra.0+0x1db/0x490 [bcachefs] uptodate 0 locks_want 2 May 09 22:45:02 sharon kernel: l=0 locks intent seq 4 node ffff8bd700c93600 May 09 22:45:02 sharon kernel: l=1 locks unlocked seq 1712 node ffff8bd6fd5e7a00 May 09 22:45:02 sharon kernel: l=2 locks unlocked seq 2295 node ffff8bd6cc725400 May 09 22:45:02 sharon kernel: l=3 locks unlocked seq 0 node 0000000000000000 Evacuate walks btree nodes with bch2_btree_iter_next_node() and rewrites them, bch2_btree_update_start() upgrades the path to take intent locks as far as it needs to. But next_node() does low level unlock/relock calls on individual nodes, and didn't handle the case where a path is supposed to be holding multiple intent locks. If a path has locks_want > 1, it needs to be either holding locks on all the btree nodes (at each level) requested, or none of them. Fix this with a bch2_btree_path_downgrade(). Signed-off-by: Kent Overstreet --- diff --git a/fs/bcachefs/btree_iter.c b/fs/bcachefs/btree_iter.c index 59fa527ac6854..9c9bc7b6c7127 100644 --- a/fs/bcachefs/btree_iter.c +++ b/fs/bcachefs/btree_iter.c @@ -1971,6 +1971,12 @@ struct btree *bch2_btree_iter_next_node(struct btree_trans *trans, struct btree_ return NULL; } + /* + * We don't correctly handle nodes with extra intent locks here: + * downgrade so we don't violate locking invariants + */ + bch2_btree_path_downgrade(trans, path); + if (!bch2_btree_node_relock(trans, path, path->level + 1)) { __bch2_btree_path_unlock(trans, path); path->l[path->level].b = ERR_PTR(-BCH_ERR_no_btree_node_relock);