From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@redhat.com>
Cc: Yi Zhang <yi.zhang@redhat.com>,
Steffen Maier <maier@linux.ibm.com>,
linux-block <linux-block@vger.kernel.org>,
Linux-Next Mailing List <linux-next@vger.kernel.org>,
linux-scsi <linux-scsi@vger.kernel.org>
Subject: Re: [bug report] WARNING: CPU: 1 PID: 1386 at block/blk-mq-sched.c:432 blk_mq_sched_insert_request+0x54/0x178
Date: Wed, 3 Nov 2021 09:12:07 -0600 [thread overview]
Message-ID: <4542eb75-aa3a-23dc-699f-c6aec613c613@kernel.dk> (raw)
In-Reply-To: <YYKmIgHttlxudYCA@T590>
On 11/3/21 9:09 AM, Ming Lei wrote:
> On Wed, Nov 03, 2021 at 09:03:02AM -0600, Jens Axboe wrote:
>> On 11/3/21 8:57 AM, Ming Lei wrote:
>>> On Wed, Nov 03, 2021 at 09:59:02PM +0800, Yi Zhang wrote:
>>>> On Wed, Nov 3, 2021 at 7:59 PM Jens Axboe <axboe@kernel.dk> wrote:
>>>>>
>>>>> On 11/2/21 9:54 PM, Jens Axboe wrote:
>>>>>> On Nov 2, 2021, at 9:52 PM, Ming Lei <ming.lei@redhat.com> wrote:
>>>>>>>
>>>>>>> On Tue, Nov 02, 2021 at 09:21:10PM -0600, Jens Axboe wrote:
>>>>>>>>> On 11/2/21 8:21 PM, Yi Zhang wrote:
>>>>>>>>>>>
>>>>>>>>>>> Can either one of you try with this patch? Won't fix anything, but it'll
>>>>>>>>>>> hopefully shine a bit of light on the issue.
>>>>>>>>>>>
>>>>>>>>> Hi Jens
>>>>>>>>>
>>>>>>>>> Here is the full log:
>>>>>>>>
>>>>>>>> Thanks! I think I see what it could be - can you try this one as well,
>>>>>>>> would like to confirm that the condition I think is triggering is what
>>>>>>>> is triggering.
>>>>>>>>
>>>>>>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>>>>>>> index 07eb1412760b..81dede885231 100644
>>>>>>>> --- a/block/blk-mq.c
>>>>>>>> +++ b/block/blk-mq.c
>>>>>>>> @@ -2515,6 +2515,8 @@ void blk_mq_submit_bio(struct bio *bio)
>>>>>>>> if (plug && plug->cached_rq) {
>>>>>>>> rq = rq_list_pop(&plug->cached_rq);
>>>>>>>> INIT_LIST_HEAD(&rq->queuelist);
>>>>>>>> + WARN_ON_ONCE(q->elevator && !(rq->rq_flags & RQF_ELV));
>>>>>>>> + WARN_ON_ONCE(!q->elevator && (rq->rq_flags & RQF_ELV));
>>>>>>>> } else {
>>>>>>>> struct blk_mq_alloc_data data = {
>>>>>>>> .q = q,
>>>>>>>> @@ -2535,6 +2537,8 @@ void blk_mq_submit_bio(struct bio *bio)
>>>>>>>> bio_wouldblock_error(bio);
>>>>>>>> goto queue_exit;
>>>>>>>> }
>>>>>>>> + WARN_ON_ONCE(q->elevator && !(rq->rq_flags & RQF_ELV));
>>>>>>>> + WARN_ON_ONCE(!q->elevator && (rq->rq_flags & RQF_ELV));
>>>>>>>
>>>>>>> Hello Jens,
>>>>>>>
>>>>>>> I guess the issue could be the following code run without grabbing
>>>>>>> ->q_usage_counter from blk_mq_alloc_request() and blk_mq_alloc_request_hctx().
>>>>>>>
>>>>>>> .rq_flags = q->elevator ? RQF_ELV : 0,
>>>>>>>
>>>>>>> then elevator is switched to real one from none, and check on q->elevator
>>>>>>> becomes not consistent.
>>>>>>
>>>>>> Indeed, that’s where I was going with this. I have a patch, testing it
>>>>>> locally but it’s getting late. Will send it out tomorrow. The nice
>>>>>> benefit is that it allows dropping the weird ref get on plug flush,
>>>>>> and batches getting the refs as well.
>>>>>
>>>>> Yi/Steffen, can you try pulling this into your test kernel:
>>>>>
>>>>> git://git.kernel.dk/linux-block for-next
>>>>>
>>>>> and see if it fixes the issue for you. Thanks!
>>>>
>>>> It still can be reproduced with the latest linux-block/for-next, here is the log
>>>>
>>>> fab2914e46eb (HEAD, new/for-next) Merge branch 'for-5.16/drivers' into for-next
>>>
>>> Hi Yi,
>>>
>>> Please try the following change:
>>>
>>>
>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>> index e1e64964a31b..eb634a9c61ff 100644
>>> --- a/block/blk-mq.c
>>> +++ b/block/blk-mq.c
>>> @@ -494,7 +494,6 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
>>> .q = q,
>>> .flags = flags,
>>> .cmd_flags = op,
>>> - .rq_flags = q->elevator ? RQF_ELV : 0,
>>> .nr_tags = 1,
>>> };
>>> struct request *rq;
>>> @@ -504,6 +503,7 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
>>> if (ret)
>>> return ERR_PTR(ret);
>>>
>>> + data.rq_flags = q->elevator ? RQF_ELV : 0,
>>> rq = __blk_mq_alloc_requests(&data);
>>> if (!rq)
>>> goto out_queue_exit;
>>> @@ -524,7 +524,6 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
>>> .q = q,
>>> .flags = flags,
>>> .cmd_flags = op,
>>> - .rq_flags = q->elevator ? RQF_ELV : 0,
>>> .nr_tags = 1,
>>> };
>>> u64 alloc_time_ns = 0;
>>> @@ -551,6 +550,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
>>> ret = blk_queue_enter(q, flags);
>>> if (ret)
>>> return ERR_PTR(ret);
>>> + data.rq_flags = q->elevator ? RQF_ELV : 0,
>>
>> Don't think that will compile, but I guess the point is that we can't do
>
> It can compile.
s/,/;
for the new assignments.
>> this assignment before queue enter, in case we're in the midst of
>> switching schedulers. Which is indeed a valid concern.
>
> Yeah, for scsi, real io sched is switched when adding disk, before
> that, the passthrough command need to see consistent q->elevator.
Yeah, I agree that the problem is most certainly there. Guess I'm just
surprised the timing works out reliably, but it sure looks like it.
--
Jens Axboe
next prev parent reply other threads:[~2021-11-03 15:12 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAHj4cs-NUKzGj5pgzRhDgdrGGbgPBqUoQ44+xgvk6njH9a_RYQ@mail.gmail.com>
2021-11-02 19:00 ` [bug report] WARNING: CPU: 1 PID: 1386 at block/blk-mq-sched.c:432 blk_mq_sched_insert_request+0x54/0x178 Steffen Maier
2021-11-02 19:02 ` Jens Axboe
2021-11-02 20:03 ` Jens Axboe
2021-11-03 2:21 ` Yi Zhang
2021-11-03 3:21 ` Jens Axboe
2021-11-03 3:51 ` Ming Lei
2021-11-03 3:54 ` Jens Axboe
2021-11-03 4:00 ` Yi Zhang
2021-11-03 19:03 ` Jens Axboe
2021-11-05 11:13 ` Yi Zhang
2021-11-03 11:59 ` Jens Axboe
2021-11-03 13:59 ` Yi Zhang
2021-11-03 14:26 ` Jens Axboe
2021-11-03 14:57 ` Ming Lei
2021-11-03 15:03 ` Jens Axboe
2021-11-03 15:09 ` Ming Lei
2021-11-03 15:12 ` Jens Axboe [this message]
2021-11-03 15:10 ` Jens Axboe
2021-11-03 15:16 ` Ming Lei
2021-11-03 15:41 ` Jens Axboe
2021-11-03 15:49 ` Jens Axboe
2021-11-03 16:09 ` Ming Lei
2021-11-03 16:36 ` Jens Axboe
[not found] ` <CGME20211103032116epcas2p13b9f3fad0fe84f58c9b7f36320c71854@epcms2p2>
2021-11-03 3:28 ` Daejun Park
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