Re: [RFC PATCH 1/3] mmc: sdio: Don't use abort-able claim host method from SDIO IRQ thread

[Ulf Hansson <ulf.hansson@linaro.org>]

On 12 May 2017 at 09:42, Adrian Hunter <adrian.hunter@intel.com> wrote:
> On 11/05/17 15:39, Ulf Hansson wrote:
>> In a step to simplify the use of the lock, mmc_claim|release_host(), let's
>> change the SDIO IRQ thread to move away from using the abort-able claim
>> host method.
>>
>> In the SDIO IRQ thread case, we can instead check the numbers of SDIO IRQs
>> that are currently claimed via host->sdio_irqs, as this field is protected
>> from updates unless the host is claimed. When host->sdio_irqs has become
>> zero, it means the SDIO func driver(s) has released the SDIO IRQ, then we
>> can bail out and stop running the SDIO IRQ thread.
>
> Does that work?  It looks a like kthread_stop() will wait on the thread,
> which is waiting to claim the host, which is claimed by the caller of
> sdio_card_irq_put() which called kthread_stop() i.e. deadlock.

Adrian, you are right and thanks for your analyze!

Maybe it's better that I first continue with my other series,
converting the kthread to a work/work-queue. As that makes it easier
to move away from using the abort-able claim host API.

Kind regards
Uffe

>
>>
>> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>> ---
>>  drivers/mmc/core/sdio_irq.c | 10 ++++++----
>>  include/linux/mmc/host.h    |  1 -
>>  2 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/mmc/core/sdio_irq.c b/drivers/mmc/core/sdio_irq.c
>> index 6d4b720..95f7a09 100644
>> --- a/drivers/mmc/core/sdio_irq.c
>> +++ b/drivers/mmc/core/sdio_irq.c
>> @@ -137,9 +137,13 @@ static int sdio_irq_thread(void *_host)
>>                * holding of the host lock does not cover too much work
>>                * that doesn't require that lock to be held.
>>                */
>> -             ret = __mmc_claim_host(host, &host->sdio_irq_thread_abort);
>> -             if (ret)
>> +             mmc_claim_host(host);
>> +             if (!host->sdio_irqs) {
>> +                     ret = 1;
>> +                     mmc_release_host(host);
>>                       break;
>> +             }
>> +
>>               ret = process_sdio_pending_irqs(host);
>>               host->sdio_irq_pending = false;
>>               mmc_release_host(host);
>> @@ -195,7 +199,6 @@ static int sdio_card_irq_get(struct mmc_card *card)
>>
>>       if (!host->sdio_irqs++) {
>>               if (!(host->caps2 & MMC_CAP2_SDIO_IRQ_NOTHREAD)) {
>> -                     atomic_set(&host->sdio_irq_thread_abort, 0);
>>                       host->sdio_irq_thread =
>>                               kthread_run(sdio_irq_thread, host,
>>                                           "ksdioirqd/%s", mmc_hostname(host));
>> @@ -223,7 +226,6 @@ static int sdio_card_irq_put(struct mmc_card *card)
>>
>>       if (!--host->sdio_irqs) {
>>               if (!(host->caps2 & MMC_CAP2_SDIO_IRQ_NOTHREAD)) {
>> -                     atomic_set(&host->sdio_irq_thread_abort, 1);
>>                       kthread_stop(host->sdio_irq_thread);
>>               } else if (host->caps & MMC_CAP_SDIO_IRQ) {
>>                       host->ops->enable_sdio_irq(host, 0);
>> diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h
>> index 21385ac..8a4131f 100644
>> --- a/include/linux/mmc/host.h
>> +++ b/include/linux/mmc/host.h
>> @@ -359,7 +359,6 @@ struct mmc_host {
>>       unsigned int            sdio_irqs;
>>       struct task_struct      *sdio_irq_thread;
>>       bool                    sdio_irq_pending;
>> -     atomic_t                sdio_irq_thread_abort;
>>
>>       mmc_pm_flag_t           pm_flags;       /* requested pm features */
>>
>>
>