linux-kernel - Re: [PATCH] mmc: fix host release issue after discard operation

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Date:	Fri, 25 Oct 2013 17:40:32 -0700
From:	"Ray Jui" <rjui@...adcom.com>
To:	"Seungwon Jeon" <tgih.jun@...sung.com>,
	"'Chris Ball'" <cjb@...top.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: fix host release issue after discard operation

On 10/25/2013 3:42 AM, Seungwon Jeon wrote:
> Hi Ray,
>
> On Fri, October 25, 2013, Ray Jui wrote:
>> Under function mmc_blk_issue_rq, after an MMC discard operation,
>> the MMC request data structure may be freed in memory. Later in
>> the same function, the check of req->cmd_flags & MMC_REQ_SPECIAL_MASK
>> is dangerous and invalid. It causes the MMC host not being released
>> when it should
>>
>> This patch fixes the issue by marking the special request down before
>> the discard/flush operation
>>
>> Reported by: Harold (SoonYeal) Yang <haroldsy@...adcom.com>
>> Signed-off-by: Ray Jui <rjui@...adcom.com>
>> ---
>>   drivers/mmc/card/block.c |    8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
>> index 1a3163f..9e8e970 100644
>> --- a/drivers/mmc/card/block.c
>> +++ b/drivers/mmc/card/block.c
>> @@ -1954,7 +1954,7 @@ static int mmc_blk_issue_rw_rq(struct mmc_queue *mq, struct request *rqc)
>>
>>   static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
>>   {
>> -	int ret;
>> +	int ret, req_is_special = 0;
> It would be better to use boolean?
>
> Either, in a different way, I considered to save the cmd_flags like below.
> unsigned int cmd_flags = req ? req->cmd_flags : 0;
>
> Then, we could replace several 'if statement' without dereference.
> if (req && req->cmd_flags & REQ_DISCARD) -> if (cmd_flags & REQ_DISCARD)
>
> Just my suggestion.
>
> Thanks,
> Seungwon Jeon
>>   	struct mmc_blk_data *md = mq->data;
>>   	struct mmc_card *card = md->queue.card;
>>   	struct mmc_host *host = card->host;
>> @@ -1973,6 +1973,10 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
>>   		goto out;
>>   	}
>>
>> +	/* mark special request here since req may be freed later */
>> +	if (req && (req->cmd_flags & MMC_REQ_SPECIAL_MASK))
>> +		req_is_special = 1;
>> +
>>   	mq->flags &= ~MMC_QUEUE_NEW_REQUEST;
>>   	if (req && req->cmd_flags & REQ_DISCARD) {
>>   		/* complete ongoing async transfer before issuing discard */
>> @@ -1999,7 +2003,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
>>
>>   out:
>>   	if ((!req && !(mq->flags & MMC_QUEUE_NEW_REQUEST)) ||
>> -	     (req && (req->cmd_flags & MMC_REQ_SPECIAL_MASK)))
>> +	     req_is_special)
>>   		/*
>>   		 * Release host when there are no more requests
>>   		 * and after special request(discard, flush) is done.
>> --
>> 1.7.9.5
>
>
Hi Seungwon,

I like your suggestion. It makes the code simpler. I'll make the change 
and submit patch v2.

Thanks,

Ray Jui

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