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/include/linux/mmc/card.h b/include/linux/mmc/card.h
index de73778..8ef3300 100644
--- a/include/linux/mmc/card.h
+++ b/include/linux/mmc/card.h
@@ -308,6 +308,7 @@
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)