From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH 01/15] blk-cgroup: don't defer blkg_free to a workqueue
Date: Sat, 28 Jan 2023 23:12:13 +0800
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References: <20230124065716.152286-1-hch@lst.de>
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To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>, linux-block@vger.kernel.org, cgroups@vger.kernel.org, Andreas Herrmann <aherrmann@suse.de>, ming.lei@redhat.com

On Tue, Jan 24, 2023 at 07:57:01AM +0100, Christoph Hellwig wrote:
> Now that blk_put_queue can be called from process context, there is no

s/process/atomic?

> need for the asynchronous execution.
> 
> This effectively reverts commit d578c770c85233af592e54537f93f3831bde7e9a.

blkg_free() can be called with ->queue_lock, and:

- del_timer_sync(&tg->service_queue.pending_timer) is called from throtl_pd_free().

- queue_lock is required by throtl_pending_timer_fn

So there is deadlock risk if the above commit is reverted.

Thanks,
Ming