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

Adrian Hunter
2020-05-07T11:48:28Z

On 6/05/20 5:34 pm, Veerabhadrarao Badiganti wrote:
> From: Sarthak Garg <sartgarg@codeaurora.org>
>
> 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@vger.kernel.org> # v4.19+
> Suggested-by: Sahitya Tummala <stummala@codeaurora.org>
> Signed-off-by: Sarthak Garg <sartgarg@codeaurora.org>
> ---
> 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;
> }
>