Re: [PATCH] mmc: dw_mmc: enable MMC_CAP_DONE_COMPLETE

[Shawn Lin <shawn.lin@linux.dev>]

Hi Marek,

在 2026/11/11 星期三 3:28, Marek Szyprowski 写道:
> On 13.10.2026 09:24, Shawn Lin wrote:
>> All requests issued by dw_mmc are completed from dw_mci_work_func(),
>> which runs from the system_bh_wq workqueue. It is therefore preemptible
>> context and host->lock is dropped before the completion, see
>> mmc_request_done() in dw_mci_request_end().
>>
>> The dw_mci_interrupt and the dw_mci_watchdog_fn never call mmc_request_done()
>> directly. So every request is completed from a sleepable context with no
>> spinlock held.
>>
>> This is exactly the contract required by MMC_CAP_DONE_COMPLETE, which was
>> introduced for hosts that can complete requests within mmc_request_done()
>> without deferring to the core's complete_work.
>>
>> Without the flag, the core records the finished request in
>> mq->complete_req and queues mq->complete_work, i.e. a second workqueue
>> dispatch plus an extra context switch per request. With the flag,
>> mmc_blk_mq_req_done() completes the request directly via
>> mmc_blk_mq_post_req() -> blk_mq_complete_request(), and a following
>> request completes the previous one inline from mmc_blk_rw_wait().
>>
>> Measured on an RK3576 SD card (dw_mmc) with:
>>
>>    perf record -a -g -F 999 -- sleep 30
>>    perf report --stdio -g graph,0.5,caller
>>
>> fio: 4k randread, ioengine=libaio
>>
>> Without the flag, the completion hot path is:
>>
>>    mmc_request_done -> mmc_blk_mq_req_done -> queue_work_on      (~4.3%)
>>    ... -> mmc_blk_mq_complete_work            (kworker/5:1H-mm, ~18.4%)
>>         -> mmc_blk_mq_complete_prev_req -> mmc_blk_mq_post_req
>>
>> with the flag the workqueue round trip disappears completely: there is no
>> queue_work_on and no mmc_blk_mq_complete_work in the profile anymore, and
>> the previous request is completed inline:
>>
>>    mmc_blk_mq_issue_rq -> mmc_blk_mq_post_req -> mmc_blk_mq_complete_rq
>>                                                    -> __blk_mq_end_request
>>
>> This can remove a redundant workqueue dispatch and context switch per completed
>> request.
>>
>> Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
> 
> 
> This patch landed yesterday in linux-next as commit 80636b762eec ("mmc: dw_mmc:
> enable MMC_CAP_DONE_COMPLETE"). In my tests I found that it causes serious
> problems. I found that it is responsible for corrupting root filesystem and/or
> journal.
> Reverting this on top of linux-next fixes the issue. Unfortunately I didn't find
> what mmc access pattern causes the corruption, but running my tests and rebooting
> boards 2 or 3 times usually ended in breaking it.
> 
> 
> There must some corner case missed in the analysis behind this patch.
> 

Thansk for testing.

I have tested this patch in my local product environment for several
days and did not trigger the issue. Of course, I have also been keeping
an eye on whether the Linux-next branch can reproduce the problem on
other platforms, because frankly speaking, this is the first controller
that is about to enable this mmc block multi-queue internal mechanism,
meaning this mechanism has not undergone rigorous large-scale deployment
testing. Could you please help test the following patch to see if it
resolves your issue?

--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -2248,6 +2248,7 @@ static void mmc_blk_mq_req_done(struct mmc_request 
*mrq)

         /* Take the recovery path for errors or urgent background 
operations */
         if (mmc_blk_rq_error(&mqrq->brq) ||
+           mmc_blk_card_busy(mq->card, req) ||
             mmc_blk_urgent_bkops_needed(mq, mqrq)) {
                 spin_lock_irqsave(&mq->lock, flags);
                 mq->recovery_needed = true;


> 
> 
>> ---
>>
>>   drivers/mmc/host/dw_mmc.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index ff0b25d..bec777b 100644
>> --- a/drivers/mmc/host/dw_mmc.c
>> +++ b/drivers/mmc/host/dw_mmc.c
>> @@ -2945,6 +2945,8 @@ static int dw_mci_init_host_caps(struct dw_mci *host)
>>   	if (mmc->caps & MMC_CAP_SDIO_IRQ)
>>   		mmc->caps2 |= MMC_CAP2_SDIO_IRQ_NOTHREAD;
>>   
>> +	mmc->caps |= MMC_CAP_DONE_COMPLETE;
>> +
>>   	return 0;
>>   }
>>   
> 
> Best regards