bcachefs: Clear should_be_locked before unlock in key_cache_drop()

We're adding new should_be_locked assertions, also add a comment
explaining why clearing should_be_locked is safe here.

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

diff --git a/fs/bcachefs/btree_key_cache.c b/fs/bcachefs/btree_key_cache.c
index b8efe2fddbc4418ed03e5986bc826777fa221886..9948d0e4d442c14e80c5d67354e4cb2d6d6d8e00 100644 (file)
--- a/fs/bcachefs/btree_key_cache.c
+++ b/fs/bcachefs/btree_key_cache.c
@@ -646,9 +646,16 @@ void bch2_btree_key_cache_drop(struct btree_trans *trans,
        unsigned i;
        trans_for_each_path(trans, path2, i)
                if (path2->l[0].b == (void *) ck) {
+                       /*
+                        * It's safe to clear should_be_locked here because
+                        * we're evicting from the key cache, and we still have
+                        * the underlying btree locked: filling into the key
+                        * cache would require taking a write lock on the btree
+                        * node
+                        */
+                       path2->should_be_locked = false;
                        __bch2_btree_path_unlock(trans, path2);
                        path2->l[0].b = ERR_PTR(-BCH_ERR_no_btree_node_drop);
-                       path2->should_be_locked = false;
                        btree_path_set_dirty(path2, BTREE_ITER_NEED_TRAVERSE);
                }