Re: 4.8-rc1 REGRESSION mmc-blk triggers WARN_ON(!host->claimed), related to: "drivers: use req op accessor" ?

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 22-08-16 18:09, Mike Christie wrote:
> On 08/21/2016 10:15 AM, Hans de Goede wrote:
>> Hi All,
>>
>> With 4.8-rc1 I'm seeing WARN_ON(!host->claimed) triggering in both
>> mmc_start_request() as well as in mmc_release_host(). The first
>> indicating that we're executing mmc commands without doing
>> mmc_claim_host() and the second one indicating that we're
>> releasing the host without having claimed it first.
>>
>> The backtraces all point to mmc_blk_issue_rq(). I've done
>> a very naive hack / workaround:
>>
>> --- a/drivers/mmc/card/block.c
>> +++ b/drivers/mmc/card/block.c
>> @@ -2151,9 +2151,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq,
>> struct request *req)
>>      struct mmc_host *host = card->host;
>>      unsigned long flags;
>>
>> -    if (req && !mq->mqrq_prev->req)
>> -        /* claim host only for the first request */
>> -        mmc_get_card(card);
>> +    mmc_get_card(card);
>>
>>      ret = mmc_blk_part_switch(card, md);
>>      if (ret) {
>> @@ -2190,15 +2188,8 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq,
>> struct request *req)
>>      }
>>
>>  out:
>> -    if ((!req && !(mq->flags & MMC_QUEUE_NEW_REQUEST)) ||
>> -        mmc_req_is_special(req))
>> -        /*
>> -         * Release host when there are no more requests
>> -         * and after special request(discard, flush) is done.
>> -         * In case sepecial request, there is no reentry to
>> -         * the 'mmc_blk_issue_rq' with 'mqrq_prev->req'.
>> -         */
>> -        mmc_put_card(card);
>> +    mmc_put_card(card);
>> +
>>      return ret;
>>  }
>>
>>
>> Which fixes this, further pointing to the somewhat magical claim / release
>> code in mmc_blk_issue_rq() being the culprit.
>>
>> Looking at recent commits these 2 stand out as possible causes of this:
>>
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c2df40dfb8c015211ec55f4b1dd0587f875c7b34
>>
>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3a5e02ced11e22ecd9da3d6710afe15bcfee1d10
>>
>>
>> I've the feeling that one of these is making mmc_blk_issue_rq() not
>> claiming
>> the host while it should do so ...
>>
>
> There is a bug with those patches and the secure discard ones where when
> REQ_OP_SECURE_ERASE is sent, mmc_put_card above will not be called, and
> they will be treated as normal requests instead of special one so the
> drivers lists are not executed properly.

Actually the problem seems to be mmc_get_card not getting called while it
should at the top of mmc_blk_issue_rq, I first get a WARN_ON(!host->claimed)
triggering in mmc_start_request (so missing mmc_card_get) and then
in mmc_release_host (mmc_card_put called without mc_card_get being called
first).

> The patch in Jens's tree
> https://git.kernel.org/cgit/linux/kernel/git/axboe/linux-block.git/commit/?h=for-linus&id=7afafc8a44bf0ab841b17d450b02aedb3a138985
> fixes the issue.

I've tried 4.8-rc3 with my hack drop and this commit cherry-picked,
but the problem is still there, so this patch does not fix it.

Regards,

Hans