On Fri, Jul 22, 2022 at 01:22:23PM +0800, Liu Song wrote: > From: Liu Song <liusong@xxxxxxxxxxxxxxxxx> > > If "blk_mq_get_tag" returns BLK_MQ_NO_TAG because the value of > "tags->nr_reserved_tags" is 0, it will fall into an infinite loop in > "__blk_mq_alloc_requests", so borrow BLK_MQ_REQ_NOWAIT to exit the loop. That means the driver calling blk_mq_alloc_request has a bug, and we should not work round that in the low level tag allocation path. If we want to be nice we can add a WARN_ON before going all the way down into the tag allocator, something like: diff --git a/block/blk-mq.c b/block/blk-mq.c index 92aae03103b74..d6c7e2ece025f 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -520,6 +520,10 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op, struct request *rq; int ret; + if (WARN_ON_ONCE((flags & BLK_MQ_REQ_RESERVED) && + !q->tag_set->reserved_tags)) + return ERR_PTR(-EINVAL); + ret = blk_queue_enter(q, flags); if (ret) return ERR_PTR(ret);
