> This is how I understand it: > > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -996,6 +996,7 @@ static void loop_queue_work(struct loop_device *lo, struct loop_cmd *cmd) > rb_insert_color(&worker->rb_node, &lo->worker_tree); > queue_work: > if (worker) { > + WARN_ON_ONCE(worker->blkcg_css != cmd->blkcg_css); Yes, this is correct. Though the check here seems a bit obvious to me - it must be correct because we assign worker above: if (cur_worker->blkcg_css == cmd->blkcg_css) { worker = cur_worker; break; or when we construct the worker: worker->blkcg_css = cmd->blkcg_css; I think this WARN_ON_ONCE check might be more interesting in loop_process_work which invokes loop_handle_cmd and actually uses cmd->blkcg_css. In any event, your understanding is correct here. > /* > * We need to remove from the idle list here while > * holding the lock so that the idle timer doesn't > @@ -2106,6 +2107,8 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx, > cmd->memcg_css = NULL; > #ifdef CONFIG_BLK_CGROUP > if (rq->bio && rq->bio->bi_blkg) { > + /* reference to blkcg_css will be held by loop_worker (outlives > + * cmd) or it is the eternal root css */ Yes, this is correct. Feel free to add my Acked-by to such a patch