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);
+
Hi，
It is a reasonable approach to prevent abnormal alloc from going down,
but this is a very rare exception after all, and above modification is
checked
every alloc request, which seems to be a bit excessive overhead.
After the rare exception occurs and fix it, the impact on the alloc
request will be lower.
Thanks
ret = blk_queue_enter(q, flags);
if (ret)
return ERR_PTR(ret);
