Re: [PATCH] blk-mq: put driver tag when this request is completed

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hi Ming,

On 02.07.2020 03:22, Ming Lei wrote:
> On Wed, Jul 01, 2020 at 04:16:32PM +0200, Marek Szyprowski wrote:
>> On 01.07.2020 15:45, Ming Lei wrote:
>>> On Wed, Jul 01, 2020 at 03:01:03PM +0200, Marek Szyprowski wrote:
>>>> On 29.06.2020 11:47, Ming Lei wrote:
>>>>> It is natural to release driver tag when this request is completed by
>>>>> LLD or device since its purpose is for LLD use.
>>>>>
>>>>> One big benefit is that the released tag can be re-used quicker since
>>>>> bio_endio() may take too long.
>>>>>
>>>>> Meantime we don't need to release driver tag for flush request.
>>>>>
>>>>> Cc: Christoph Hellwig <hch@lst.de>
>>>>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>>>> This patch landed recently in linux-next as commit 36a3df5a4574. Sadly
>>>> it causes a regression on one of my test systems (ARM 32bit, Samsung
>>>> Exynos5422 SoC based Odroid XU3 board with eMMC). The system boots fine
>>>> and then after a few seconds every executed command hangs. No
>>>> panic/ops/any other message. I will try to provide more information asap
>>>> I find something to share. Simple reverting it in linux-next is not
>>>> possible due to dependencies.
>>> What is the exact eMMC's driver code(include the host driver)?
>> dwmmc-exynos (drivers/mmc/host/dw_mmc-exynos.c)
> Hi,
>
> Just take a quick look at mmc code, there are only two req->tag
> consumers:
>
> 1) cqhci_tag
> cqhci_tag
> 	cqhci_request
> 		host->cqe_ops->cqe_request
> 			mmc_cqe_start_req
> 	cqhci_timeout
>
> 2) mmc_hsq_request
> mmc_hsq_request
> 	host->cqe_ops->cqe_request
> 		mmc_cqe_start_req
>
> mmc_cqe_start_req() is called before issuing this request to hardware,
> so completion won't happen when the tag is used in mmc_cqe_start_req().
>
> cqhci_timeout() may race with normal completion, however looks the
> following code can handle the race correctly:
>
>          spin_lock_irqsave(&cq_host->lock, flags);
>          timed_out = slot->mrq == mrq;
>
> So still no idea why the commit causes the trouble for mmc.
>
> Do you know it is cqhci or mmc_hsh which works for dw_mmc-exynos?
> And can you apply the following patch and see if warning can be
> triggered?
>
> diff --git a/drivers/mmc/host/cqhci.c b/drivers/mmc/host/cqhci.c
> index 75934f3c117e..2cb49ecfbf34 100644
> --- a/drivers/mmc/host/cqhci.c
> +++ b/drivers/mmc/host/cqhci.c
> @@ -612,6 +612,7 @@ static int cqhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>   		goto out_unlock;
>   	}
>   
> +	WARN_ON_ONCE(cq_host->slot[tag].mrq);
>   	cq_host->slot[tag].mrq = mrq;
>   	cq_host->slot[tag].flags = 0;
>   
> diff --git a/drivers/mmc/host/mmc_hsq.c b/drivers/mmc/host/mmc_hsq.c
> index a5e05ed0fda3..11a4c1f3a970 100644
> --- a/drivers/mmc/host/mmc_hsq.c
> +++ b/drivers/mmc/host/mmc_hsq.c
> @@ -227,6 +227,7 @@ static int mmc_hsq_request(struct mmc_host *mmc, struct mmc_request *mrq)
>   		return -EBUSY;
>   	}
>   
> +	WARN_ON_ONCE(hsq->slot[tag].mrq);
>   	hsq->slot[tag].mrq = mrq;
>   
>   	/*

None of the above is even compiled for my system (I'm using 
arm/exynos_defconfig), so this must be something else.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland