Re: [PATCH] block: Fix blk_mq_try_issue_directly()

From: "jianchao.wang" <jianchao.w.wang@oracle.com>
To: Laurence Oberman <loberman@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>,
	Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Christoph Hellwig <hch@infradead.org>,
	Hannes Reinecke <hare@suse.com>,
	James Smart <james.smart@broadcom.com>,
	Ming Lei <ming.lei@redhat.com>,
	Keith Busch <keith.busch@intel.com>,
	Dongli Zhang <dongli.zhang@oracle.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] block: Fix blk_mq_try_issue_directly()
Date: Wed, 10 Apr 2019 08:51:28 +0800	[thread overview]
Message-ID: <05ce8c99-615d-e1f4-3e83-b947a31ff7be@oracle.com> (raw)
In-Reply-To: <f2703a1e76262820cbe0e40ed7110771606ec2f6.camel@redhat.com>

On 4/9/19 8:28 PM, Laurence Oberman wrote:
> On Tue, 2019-04-09 at 09:31 +0800, jianchao.wang wrote:
>>
>> On 4/8/19 10:36 AM, jianchao.wang wrote:
>>>
>>>
>>> On 4/8/19 10:07 AM, jianchao.wang wrote:
>>>> Hi Bart
>>>>
>>>> On 4/4/19 4:11 AM, Bart Van Assche wrote:
>>>>> If blk_mq_try_issue_directly() returns BLK_STS*_RESOURCE that
>>>>> means that
>>>>> the request has not been queued and that the caller should
>>>>> retry to submit
>>>>> the request. Both blk_mq_request_bypass_insert() and
>>>>> blk_mq_sched_insert_request() guarantee that a request will be
>>>>> processed.
>>>>> Hence return BLK_STS_OK if one of these functions is called.
>>>>> This patch
>>>>> avoids that blk_mq_dispatch_rq_list() crashes when using dm-
>>>>> mpath.
>>>>
>>>> Sorry, I seem to miss the original mail list that reported this
>>>> issue.
>>>> As your comment, it looks like that the request is handled again
>>>> when
>>>> the blk_mq_try_issue_directly return BLK_STS*_RESOURCE, right ?
>>>>
>>>> The usage of this helper interface is,
>>>> if care about the return value and want to handle the request
>>>> yourself when
>>>> return BLK_STS*_RESOURCE, pass 'byass' as true.
>>>> otherwise, just pass 'bypass' as false, then
>>>> blk_mq_try_issue_directly would
>>>> take over all of the work including requeue or complete the
>>>> request.
>>>>
>>>> if dm-mpath case, the driver should only invoke
>>>> dm_dispatch_clone_request,
>>>> the 'bypass' parameter should only be true.
>>>> as the blk_mq_try_issue_directly,
>>>> it would return BLK_STS_OK when have to insert the request,
>>>> otherwise,
>>>> it would do nothing but return BLK_STS*_RESOURCE.
>>>>
>>>> Would you please show the cause that the dm-mpath driver invoke
>>>> blk_mq_try_issue_direclty
>>>> with 'bypass == false' ?
>>>>
>>>
>>> The issue seems to be here,
>>>
>>> blk_mq_try_issue_directly
>>>
>>>
>>>     if (unlikely(blk_mq_hctx_stopped(hctx) ||
>>> blk_queue_quiesced(q))) {
>>>         run_queue = false;
>>>         bypass = false;          //------> HERE !!!
>>>         goto out_unlock;
>>>     }
>>>
>>>
>>>     case BLK_STS_RESOURCE:
>>>         if (force) {
>>>             blk_mq_request_bypass_insert(rq, run_queue);
>>>             ret = bypass ? BLK_STS_OK : ret;
>>>         } else if (!bypass) {
>>>             blk_mq_sched_insert_request(rq, false,
>>>                             run_queue, false);
>>>         }
>>>         break;
>>>
>>> Then the request will be inserted and blk_mq_try_issue_dreictly
>>> returns BLK_STS_RESOURCE.
>>>
>>>
>>> Could following patch fix the issue ?
>>
>> Hi Laurence
>>
>> Would you please test this patch to see whether the issue could be
>> fixed ?
>>
>> Thanks
>> Jianchao
>>>
>>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>>> index a9c1816..a3394f2 100644
>>> --- a/block/blk-mq.c
>>> +++ b/block/blk-mq.c
>>> @@ -1813,7 +1813,7 @@ blk_status_t blk_mq_try_issue_directly(struct
>>> blk_mq_hw_ctx *hctx,
>>>          */
>>>         if (unlikely(blk_mq_hctx_stopped(hctx) ||
>>> blk_queue_quiesced(q))) {
>>>                 run_queue = false;
>>> -               bypass = false;
>>> +               force = true;
>>>                 goto out_unlock;
>>>         }
>>>
>>> Thanks
>>> Jianchao
>>>
...
> Hello Sir
> I think Jens already took the revert patch though.
> I will try this when I gat a chance.
> Need to wait until I can reboot the targetserver again.

Thanks so much for your help. Please share the test result here.
I will get the reverted patches back after that.

Thanks
Jianchao