Re: [PATCH -next v2] blk-mq: fix panic during blk_mq_run_work_fn()

From: "yukuai (C)" <yukuai3@huawei.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: <axboe@kernel.dk>, <linux-block@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
Subject: Re: [PATCH -next v2] blk-mq: fix panic during blk_mq_run_work_fn()
Date: Fri, 20 May 2022 20:01:31 +0800	[thread overview]
Message-ID: <8e6a806b-f42e-319b-e6c8-de1f07befce2@huawei.com> (raw)
In-Reply-To: <Yod93DOdYosa+SvS@T590>

在 2022/05/20 19:39, Ming Lei 写道:

> 
> In short:
> 
> 1) run queue can be in-progress during cleanup queue, or returns from
> cleanup queue; we drain it in both blk_cleanup_queue() and
> disk_release_mq(), see commit 2a19b28f7929 ("blk-mq: cancel blk-mq dispatch
> work in both blk_cleanup_queue and disk_release()")
I understand that, however, there is no garantee new 'hctx->run_work'
won't be queued after 'drain it', for this crash, I think this is how
it triggered:

assum that there is no io, while some bfq_queue is still busy:

blk_cleanup_queue
  blk_freeze_queue
  blk_mq_cancel_work_sync
  cancel_delayed_work_sync(hctx1)
				blk_mq_run_work_fn -> hctx2
				 __blk_mq_run_hw_queue
				  blk_mq_sched_dispatch_requests
				   __blk_mq_do_dispatch_sched
				    blk_mq_delay_run_hw_queues
				     blk_mq_delay_run_hw_queue
				      -> add hctx1->run_work again
  cancel_delayed_work_sync(hctx2)
> 
> 2) tagset can't be touched after blk_cleanup_queue returns because
> tagset lifetime is covered by driver, which is often released after
> blk_cleanup_queue() returns.
> 
> 
> Thanks,
> Ming
> 
> .
>