From: Tejun Heo <tj@kernel.org>
To: Roman Gushchin <roman.gushchin@linux.dev>
Cc: "Chen Ridong" <chenridong@huaweicloud.com>,
"Michal Koutný" <mkoutny@suse.com>,
"Chen Ridong" <chenridong@huawei.com>,
martin.lau@linux.dev, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org, eddyz87@gmail.com, song@kernel.org,
yonghong.song@linux.dev, john.fastabend@gmail.com,
kpsingh@kernel.org, sdf@google.com, haoluo@google.com,
jolsa@kernel.org, lizefan.x@bytedance.com, hannes@cmpxchg.org,
bpf@vger.kernel.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 1/1] cgroup: fix deadlock caused by cgroup_mutex and cpu_hotplug_lock
Date: Tue, 10 Sep 2024 11:17:49 -1000 [thread overview]
Message-ID: <ZuC3femqBNufgX1D@slm.duckdns.org> (raw)
In-Reply-To: <ZuC0A98pxYc3TODM@google.com>
On Tue, Sep 10, 2024 at 09:02:59PM +0000, Roman Gushchin wrote:
...
> > > By that reasoning any holder of cgroup_mutex on system_wq makes system
> > > susceptible to a deadlock (in presence of cpu_hotplug_lock waiting
> > > writers + cpuset operations). And the two work items must meet in same
> > > worker's processing hence probability is low (zero?) with less than
> > > WQ_DFL_ACTIVE items.
>
> Right, I'm on the same page. Should we document then somewhere that
> the cgroup mutex can't be locked from a system wq context?
>
> I think thus will also make the Fixes tag more meaningful.
I think that's completely fine. What's not fine is saturating system_wq.
Anything which creates a large number of concurrent work items should be
using its own workqueue. If anything, workqueue needs to add a warning for
saturation conditions and who are the offenders.
Thanks.
--
tejun
next prev parent reply other threads:[~2024-09-10 21:17 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-17 9:33 [PATCH v3 0/1] Fix deadlock caused by cgroup_mutex and cpu_hotplug_lock Chen Ridong
2024-08-17 9:33 ` [PATCH v3 1/1] cgroup: fix " Chen Ridong
2024-08-22 0:57 ` Chen Ridong
2024-08-30 2:08 ` Chen Ridong
2024-09-09 14:19 ` Michal Koutný
2024-09-10 1:31 ` Chen Ridong
2024-09-10 21:02 ` Roman Gushchin
2024-09-10 21:17 ` Tejun Heo [this message]
2024-09-12 1:33 ` Chen Ridong
2024-09-12 5:59 ` Tejun Heo
2024-09-11 11:15 ` Hillf Danton
2024-09-26 12:53 ` Michal Koutný
2024-09-27 11:25 ` Hillf Danton
2024-09-27 14:03 ` Michal Koutný
2024-09-28 8:11 ` Tetsuo Handa
2024-09-29 1:30 ` Chen Ridong
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