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: 81196976ed94 ("mmc: block: Add blk-mq support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
index aef1185f383d42f3a3f7192b2003d521471acd18..14f3fdb8c6bb7aad30d3b9f1337afcb1f6e34f7e 100644 (file)
--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -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)

diff --git a/include/linux/mmc/card.h b/include/linux/mmc/card.h
index de7377815b6b4c9828beccd1c6a37932c8a29d0d..8ef330027b134eb9ea073f5d4e9ac82d1d1bfc29 100644 (file)
--- a/include/linux/mmc/card.h
+++ b/include/linux/mmc/card.h
@@ -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)