mmc: card: fix race with shutdown handler

There could be 2 different race conditions possible with current shutdown
handler:
1. Shutdown handler sees that there is no request in queue but mmc-cmdqd
   might have fetched the request from queue and about to issue it to
   driver.
2. Shutdown handler keeps looping in the while(1) loop as it sees request
   being pending in the request queue. But mmc-cmdqd thread doesn't wake up
   to fetch the requests from the request queue. mmc-cmdqd thread isn't
   waking up because shutdown path has stopped queue and request came into
   the queue after that. Once queue is stopped, block layer won't invoke
   the queue's ->request_fn() callback to notify driver about pending
   request.

Remedy to fix both these race condition is simple. In shutdown handler,
make sure that we drain (& complete) all the outstanding requests from the
queue and then don't allow any new requests to be queued. Block layer API
blk_cleanup_queue() precisely does what we want and this change basically
use the same API in shutdown handler.

Change-Id: I761ba6a2e2974d955bb72ff993b1cc2c32c9ec29
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>

3 files changed, 6 insertions, 34 deletions

diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
index 1ca30a1bb75d..bfd877cdb6e2 100644
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -3204,8 +3204,6 @@ out:
 	if (!ctx_info->active_reqs)
 		wake_up_interruptible(&host->cmdq_ctx.queue_empty_wq);
 
-	if (blk_queue_stopped(mq->queue) && !ctx_info->active_reqs)
-		complete(&mq->cmdq_shutdown_complete);
 	return;
 }
 
diff --git a/drivers/mmc/card/queue.c b/drivers/mmc/card/queue.c
index 05f456b0d1c1..fdbfdc0f4e3a 100644
--- a/drivers/mmc/card/queue.c
+++ b/drivers/mmc/card/queue.c
@@ -655,7 +655,6 @@ int mmc_cmdq_init(struct mmc_queue *mq, struct mmc_card *card)
 
 	blk_queue_softirq_done(mq->queue, mmc_cmdq_softirq_done);
 	INIT_WORK(&mq->cmdq_err_work, mmc_cmdq_error_work);
-	init_completion(&mq->cmdq_shutdown_complete);
 	init_completion(&mq->cmdq_pending_req_done);
 
 	blk_queue_rq_timed_out(mq->queue, mmc_cmdq_rq_timed_out);
@@ -704,7 +703,6 @@ int mmc_queue_suspend(struct mmc_queue *mq, int wait)
 	int rc = 0;
 	struct mmc_card *card = mq->card;
 	struct request *req;
-	#define SLEEP_TIME_BETWEEN_BLK_REQ_CHECK	100 /* microseconds */
 
 	if (card->cmdq_init && blk_queue_tagged(q)) {
 		struct mmc_host *host = card->host;
@@ -712,44 +710,21 @@ int mmc_queue_suspend(struct mmc_queue *mq, int wait)
 		if (test_and_set_bit(MMC_QUEUE_SUSPENDED, &mq->flags))
 			goto out;
 
-		spin_lock_irqsave(q->queue_lock, flags);
-		blk_stop_queue(q);
-		spin_unlock_irqrestore(q->queue_lock, flags);
-
-		wake_up(&host->cmdq_ctx.wait);
-
 		if (wait) {
-			while (1) {
-				spin_lock_irqsave(q->queue_lock, flags);
-				req = blk_peek_request(q);
-				spin_unlock_irqrestore(q->queue_lock, flags);
-
-				if (!req)
-					break;
-
-				/* sleep for some time before rechecking */
-				usleep_range(SLEEP_TIME_BETWEEN_BLK_REQ_CHECK,
-					SLEEP_TIME_BETWEEN_BLK_REQ_CHECK + 10);
-			}
-
-			/* Wait for already issued requests to complete */
-			if (host->cmdq_ctx.active_reqs)
-				wait_for_completion(
-						&mq->cmdq_shutdown_complete);
-
+			blk_cleanup_queue(q);
 			mq->cmdq_shutdown(mq);
 		} else {
 			spin_lock_irqsave(q->queue_lock, flags);
+			blk_stop_queue(q);
+			wake_up(&host->cmdq_ctx.wait);
 			req = blk_peek_request(q);
-			spin_unlock_irqrestore(q->queue_lock, flags);
-
-			if (req || host->cmdq_ctx.active_reqs) {
+			if (req || mq->cmdq_req_peeked ||
+			    host->cmdq_ctx.active_reqs) {
 				clear_bit(MMC_QUEUE_SUSPENDED, &mq->flags);
-				spin_lock_irqsave(q->queue_lock, flags);
 				blk_start_queue(q);
-				spin_unlock_irqrestore(q->queue_lock, flags);
 				rc = -EBUSY;
 			}
+			spin_unlock_irqrestore(q->queue_lock, flags);
 		}
 
 		goto out;
diff --git a/drivers/mmc/card/queue.h b/drivers/mmc/card/queue.h
index e67d0546346a..964262f0eb79 100644
--- a/drivers/mmc/card/queue.h
+++ b/drivers/mmc/card/queue.h
@@ -70,7 +70,6 @@ struct mmc_queue {
 	int			num_wr_reqs_to_start_packing;
 	bool			no_pack_for_random;
 	struct work_struct	cmdq_err_work;
-	struct completion	cmdq_shutdown_complete;
 
 	struct completion	cmdq_pending_req_done;
 	struct request		*cmdq_req_peeked;