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

[Ray Jui]

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@xxxxxxxxxxxx>
> > Signed-off-by: Ray Jui <rjui@xxxxxxxxxxxx>
> > ---
> >   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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