Commit dcf6e2e3 authored Feb 07, 2019 by Zachary Hays Committed by Ulf Hansson Feb 08, 2019

mmc: block: handle complete_work on separate workqueue



The kblockd workqueue is created with the WQ_MEM_RECLAIM flag set.
This generates a rescuer thread for that queue that will trigger when
the CPU is under heavy load and collect the uncompleted work.

In the case of mmc, this creates the possibility of a deadlock when
there are multiple partitions on the device as other blk-mq work is
also run on the same queue. For example:

- worker 0 claims the mmc host to work on partition 1
- worker 1 attempts to claim the host for partition 2 but has to wait
  for worker 0 to finish
- worker 0 schedules complete_work to release the host
- rescuer thread is triggered after time-out and collects the dangling
  work
- rescuer thread attempts to complete the work in order starting with
  claim host
- the task to release host is now blocked by a task to claim it and
  will never be called

The above results in multiple hung tasks that lead to failures to
mount partitions.

Handling complete_work on a separate workqueue avoids this by keeping
the work completion tasks separate from the other blk-mq work. This
allows the host to be released without getting blocked by other tasks
attempting to claim the host.

Signed-off-by: Zachary Hays <zhays@lexmark.com>
Fixes: 81196976 ("mmc: block: Add blk-mq support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

parent d6f11e7d

drivers/mmc/core/block.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -2112,7 +2112,7 @@ static void mmc_blk_mq_req_done(struct mmc_request *mrq)
		if (waiting)
		wake_up(&mq->wait);
		else
		kblockd_schedule_work(&mq->complete_work);
		queue_work(mq->card->complete_wq, &mq->complete_work);

		return;
		}
		@@ -2924,6 +2924,13 @@ static int mmc_blk_probe(struct mmc_card *card)

		mmc_fixup_device(card, mmc_blk_fixups);

		card->complete_wq = alloc_workqueue("mmc_complete",
		WQ_MEM_RECLAIM \| WQ_HIGHPRI, 0);
		if (unlikely(!card->complete_wq)) {
		pr_err("Failed to create mmc completion workqueue");
		return -ENOMEM;
		}

		md = mmc_blk_alloc(card);
		if (IS_ERR(md))
		return PTR_ERR(md);
		@@ -2987,6 +2994,7 @@ static void mmc_blk_remove(struct mmc_card *card)
		pm_runtime_put_noidle(&card->dev);
		mmc_blk_remove_req(md);
		dev_set_drvdata(&card->dev, NULL);
		destroy_workqueue(card->complete_wq);
		}

		static int _mmc_blk_suspend(struct mmc_card *card)

include/linux/mmc/card.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -308,6 +308,7 @@ struct mmc_card {
		unsigned int nr_parts;

		unsigned int bouncesz; /* Bounce buffer size */
		struct workqueue_struct complete_wq; / Private workqueue */
		};

		static inline bool mmc_large_sector(struct mmc_card *card)