From dcf6e2e38a1c7ccbc535de5e1d9b14998847499d Mon Sep 17 00:00:00 2001 From: Zachary Hays Date: Thu, 7 Feb 2019 10:03:08 -0500 Subject: [PATCH] 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 Fixes: 81196976ed94 ("mmc: block: Add blk-mq support") Cc: Signed-off-by: Ulf Hansson --- drivers/mmc/core/block.c | 10 +++++++++- include/linux/mmc/card.h | 1 + 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c index aef1185f383d..14f3fdb8c6bb 100644 --- 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 de7377815b6b..8ef330027b13 100644 --- 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) -- 2.45.2