Re: [PATCH 1/2] mmc: core: fix permanent sleep of mmcqd during card removal

[Subhash Jadavani <subhashj@codeaurora.org>]

On 1/30/2013 12:00 PM, Seungwon Jeon wrote:
> Hi Konstantin.
>
> Could you check this patch with [2/2]?
> [PATCH 2/2] mmc: block: don't start new request when the card is removed
>
> mmcqd is often sleeping with acquiring the claim(mmc_claim_host) when a card is removed.
> As a result, mmc_rescan can be blocked for the insertion of a card newly. It's a dead lock.
>
> Thanks,
> Seungwon Jeon
>
> On Tuesday, January 22, 2013, Seungwon Jeon wrote:
>> This patch is derived from 'mmc: fix async request mechanism ...'.
>> According as async transfer, a request is handled with twice mmc_start_req.
>> When the card is removed, the request is actually not issued in the first
>> mmc_start_req [__mmc_start_data_req]. And then mmc_wait_for_data_req_done
>> will come in the next mmc_start_req. But there is no event for completions.
>> wake_up_interruptible is needed in __mmc_start_data_req for the case of
>> removed card.

Hi Seungwon,

I looked at this again and i guess there is something wrong with
mmc_start_req() itself.
As per your commit text, first call to mmc_start_req() calls the
__mmc_start_data_req() function and __mmc_start_data_req() returns the
-ENOMEDIUM error (as card is removed) without starting the request on
host controller. so now in mmc_start_req(), "start_err" should be set.
But currently mmc_start_req() incorrectly marks the "host->areq" to
"areq" in even if the start_err is set which i guess is wrong. what do
you think about it?

So how about this fix? I guess this is better and it should fix the
deadlock issue as well. Do let me know you thoughts on this. If it looks
reasonable, i can post the formal patch.


diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
index 39f28af..1aa7dbe 100644
--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -546,7 +546,7 @@ struct mmc_async_req *mmc_start_req(struct mmc_host
*host,
if ((err || start_err) && areq)
mmc_post_req(host, areq->mrq, -EINVAL);

- if (err)
+ if (err || start_err)
host->areq = NULL;
else
host->areq = areq;

Regards,
Subhash

>>
>> Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
>> ---
>>  drivers/mmc/core/core.c |    1 +
>>  1 files changed, 1 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>> index 8b3a122..997b257 100644
>> --- a/drivers/mmc/core/core.c
>> +++ b/drivers/mmc/core/core.c
>> @@ -350,6 +350,7 @@ static int __mmc_start_data_req(struct mmc_host *host, struct mmc_request *mrq)
>>  	mrq->host = host;
>>  	if (mmc_card_removed(host->card)) {
>>  		mrq->cmd->error = -ENOMEDIUM;
>> +		mmc_wait_data_done(mrq);
>>  		return -ENOMEDIUM;
>>  	}
>>  	mmc_start_request(host, mrq);
>> --
>> 1.7.0.4
>
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