Re: [PATCH -v2] cgroup: fix deadlock caused by cgroup_mutex and cpu_hotplug_lock

[Roman Gushchin <roman.gushchin@linux.dev>]

On Wed, Aug 07, 2024 at 03:32:59PM +0200, Michal Koutny wrote:
> Hello.
> 
> On Sat, Jul 27, 2024 at 06:21:55PM GMT, chenridong <chenridong@huawei.com> wrote:
> > Yes, I have offered the scripts in Link(V1).
> 
> Thanks (and thanks for patience).
> There is no lockdep complain about a deadlock (i.e. some circular
> locking dependencies). (I admit the multiple holders of cgroup_mutex
> reported there confuse me, I guess that's an artifact of this lockdep
> report and they could be also waiters.)
>
> ...
>
> The change on its own (deferred cgroup bpf progs removal via
> cgroup_destroy_wq instead of system_wq) is sensible by collecting
> related objects removal together (at the same time it shouldn't cause
> problems by sharing one cgroup_destroy_wq).
> 
> But the reasoning in the commit message doesn't add up to me. There
> isn't obvious deadlock, I'd say that system is overloaded with repeated
> calls of __lockup_detector_reconfigure() and it is not in deadlock
> state -- i.e. when you stop the test, it should eventually recover.

Thanks, Michal! I've exactly same feelings about this change.