linux-kernel - Re: [PATCH v4 0/3] Fix deadlock caused by cgroup_mutex and cpu_hotplug

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Message-ID: <07168cb9-7d26-4256-bcdc-0f261aba9d53@huaweicloud.com>
Date: Sat, 21 Sep 2024 10:06:30 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Tejun Heo <tj@...nel.org>
Cc: martin.lau@...ux.dev, ast@...nel.org, daniel@...earbox.net,
 andrii@...nel.org, eddyz87@...il.com, song@...nel.org,
 yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org,
 sdf@...gle.com, haoluo@...gle.com, jolsa@...nel.org,
 lizefan.x@...edance.com, hannes@...xchg.org, roman.gushchin@...ux.dev,
 Michal Koutný <mkoutny@...e.com>, bpf@...r.kernel.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/3] Fix deadlock caused by cgroup_mutex and
 cpu_hotplug_lock



On 2024/9/21 3:23, Tejun Heo wrote:
> On Wed, Sep 18, 2024 at 05:44:47PM +0800, Chen Ridong wrote:
> ...
>>>     cgroup: fix deadlock caused by cgroup_mutex and cpu_hotplug_lock
>>>     workqueue: doc: Add a note saturating the system_wq is not permitted
>>>     workqueue: Adjust WQ_MAX_ACTIVE from 512 to 2048
>>>
>>>    Documentation/core-api/workqueue.rst | 8 ++++++--
>>>    include/linux/workqueue.h            | 2 +-
>>>    kernel/bpf/cgroup.c                  | 2 +-
>>>    kernel/cgroup/cgroup-internal.h      | 1 +
>>>    kernel/cgroup/cgroup.c               | 2 +-
>>>    5 files changed, 10 insertions(+), 5 deletions(-)
>>>
>> Friendly ping.
> 
> I don't know why but this series isn't in my inbox for some reason. Here are
> some feedbacks after looking at the thread from lore:
> 
> - Can you create a separate workqueue for cgrp->bpf.release_work instead of
>    exporting cgroup_destroy_wq? Workqueues aren't that expensive. No reason
>    to share like this.
> 
> - The patch title is rather misleading. The deadlock isn't really caused
>    between cgroup_mutex and cpu_hotplug_lock. They're just victims of
>    system_wq concurrency depletion. Can you please update accordingly?
> 
> - Can you add a new line before the note paragraph? Also, I'd say "deadlock"
>    rather than "block" to properly convey the imapct of such saturation
>    events. I don't think "eg. cgroup release work" is adding much.
> 
> Thanks.
> 

Thanks, TJ, I will do that.

Best regards,
Ridong