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

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Message-id: <001301ced16e$f2695480$d73bfd80$%jun@samsung.com>
Date:	Fri, 25 Oct 2013 19:42:48 +0900
From:	Seungwon Jeon <tgih.jun@...sung.com>
To:	'Ray Jui' <rjui@...adcom.com>, 'Chris Ball' <cjb@...top.org>
Cc:	linux-kernel@...r.kernel.org
Subject: RE: [PATCH] mmc: fix host release issue after discard operation

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

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