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

From: Ray Jui
Date: Fri Oct 25 2013 - 20:40:59 EST

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.

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)

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.

Hi Seungwon,

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


Ray Jui

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