On 8/15/25 7:02 AM, Yu Kuai wrote:
> Hi,
>
> 在 2025/08/14 20:23, Nilay Shroff 写道:
>>
>>
>> On 8/14/25 9:05 AM, Yu Kuai wrote:
>>> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>>>
>>> 1) queue_requests_store() is the only caller of
>>> blk_mq_update_nr_requests(), where queue is already freezed, no need to
>>> check mq_freeze_depth;
>>> 2) q->tag_set must be set for request_based device, and queue_is_mq() is
>>> already checked in blk_mq_queue_attr_visible(), no need to check
>>> q->tag_set.
>>> 3) During initialization, hctx->tags in initialized before queue
>>> kobject, and during del_gendisk, queue kobject is deleted before
>>> exiting hctx, hence checking hctx->tags is useless.
>>>
>>> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
>>> ---
>>> block/blk-mq.c | 11 +----------
>>> 1 file changed, 1 insertion(+), 10 deletions(-)
>>>
>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>> index b67d6c02eceb..3a219b7b3688 100644
>>> --- a/block/blk-mq.c
>>> +++ b/block/blk-mq.c
>>> @@ -4921,24 +4921,15 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
>>> {
>>> struct blk_mq_tag_set *set = q->tag_set;
>>> struct blk_mq_hw_ctx *hctx;
>>> - int ret;
>>> + int ret = 0;
>>> unsigned long i;
>>> - if (WARN_ON_ONCE(!q->mq_freeze_depth))
>>> - return -EINVAL;
>>> -
>>> - if (!set)
>>> - return -EINVAL;
>>> -
>>> if (q->nr_requests == nr)
>>> return 0;
>>> blk_mq_quiesce_queue(q);
>>> - ret = 0;
>>> queue_for_each_hw_ctx(q, hctx, i) {
>>> - if (!hctx->tags)
>>> - continue;
>> It's possible that hctx->tags is set to NULL in case no software
>> queues are mapped to the hardware queue. So it seems that this
>> check is valid. Please see blk_mq_map_swqueue().
>
> Ok, thanks for the reviw.
>
> I didn't notice this, just wonder how can this happen?
> nr_hw_queues > NR_CPUS?
>
I think typically having nr_hw_queues > NR_CPUS is not allowed.
But it's possible to have no software queues are mapped to hctx.
Check this commit 4412efecf7fd ("Revert "blk-mq: remove code for
dealing with remapping queue")
Thanks,
--Nilay
