bcachefs: Add some cond_rescheds() in shutdown path

Particularly on emergency shutdown we can end up having to clean up a
lot of dirty cached btree keys here.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_key_cache.c

@@ -581,6 +581,8 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
 	list_splice(&bc->dirty, &bc->clean);
 
 	list_for_each_entry_safe(ck, n, &bc->clean, list) {
+		cond_resched();
+
 		bch2_journal_pin_drop(&c->journal, &ck->journal);
 		bch2_journal_preres_put(&c->journal, &ck->res);
 
@@ -594,6 +596,8 @@ void bch2_fs_btree_key_cache_exit(struct btree_key_cache *bc)
 	BUG_ON(bc->nr_keys);
 
 	list_for_each_entry_safe(ck, n, &bc->freed, list) {
+		cond_resched();
+
 		list_del(&ck->list);
 		kmem_cache_free(bch2_key_cache, ck);
 	}