Re: [PATCH V1 2/2] mmc: core: Fix recursive locking issue in CQE recovery path

[Adrian Hunter]

On 6/05/20 5:34 pm, Veerabhadrarao Badiganti wrote:
> From: Sarthak Garg <sartgarg@xxxxxxxxxxxxxx>
> 
> Consider the following stack trace
> 
> -001|raw_spin_lock_irqsave
> -002|mmc_blk_cqe_complete_rq
> -003|__blk_mq_complete_request(inline)
> -003|blk_mq_complete_request(rq)
> -004|mmc_cqe_timed_out(inline)
> -004|mmc_mq_timed_out
> 
> mmc_mq_timed_out acquires the queue_lock for the first
> time. The mmc_blk_cqe_complete_rq function also tries to acquire
> the same queue lock resulting in recursive locking where the task
> is spinning for the same lock which it has already acquired leading
> to watchdog bark.
> 
> Fix this issue with the lock only for the required critical section.
> 
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.19+
> Suggested-by: Sahitya Tummala <stummala@xxxxxxxxxxxxxx>
> Signed-off-by: Sarthak Garg <sartgarg@xxxxxxxxxxxxxx>
> ---
>  drivers/mmc/core/queue.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
> index 25bee3d..72bef39 100644
> --- a/drivers/mmc/core/queue.c
> +++ b/drivers/mmc/core/queue.c
> @@ -107,7 +107,7 @@ static enum blk_eh_timer_return mmc_cqe_timed_out(struct request *req)
>  	case MMC_ISSUE_DCMD:
>  		if (host->cqe_ops->cqe_timeout(host, mrq, &recovery_needed)) {
>  			if (recovery_needed)
> -				__mmc_cqe_recovery_notifier(mq);
> +				mmc_cqe_recovery_notifier(mrq);
>  			return BLK_EH_RESET_TIMER;
>  		}
>  		/* No timeout (XXX: huh? comment doesn't make much sense) */
> @@ -131,12 +131,13 @@ static enum blk_eh_timer_return mmc_mq_timed_out(struct request *req,
>  
>  	spin_lock_irqsave(&mq->lock, flags);
>  
> -	if (mq->recovery_needed || !mq->use_cqe || host->hsq_enabled)
> +	if (mq->recovery_needed || !mq->use_cqe || host->hsq_enabled) {
>  		ret = BLK_EH_RESET_TIMER;
> -	else
> +		spin_unlock_irqrestore(&mq->lock, flags);
> +	} else {
> +		spin_unlock_irqrestore(&mq->lock, flags);
>  		ret = mmc_cqe_timed_out(req);
> -
> -	spin_unlock_irqrestore(&mq->lock, flags);
> +	}

This looks good, but I think there needs to be another change also.  I will
send a patch for that, but in the meantime maybe you could straighten up the
code flow through the spinlock e.g.

	spin_lock_irqsave(&mq->lock, flags);
	ignore = mq->recovery_needed || !mq->use_cqe || host->hsq_enabled;
	spin_unlock_irqrestore(&mq->lock, flags);

	return ignore ? BLK_EH_RESET_TIMER : mmc_cqe_timed_out(req);

And add a fixes tag.

>  
>  	return ret;
>  }
>