linux-kernel - Re: [PATCH] cgroup: replace global percpu_rwsem with signal_struct->group

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Message-ID: <rgjlqyeqcgi43crx4mqpwi7tqxqgy7bkmjbpv7t6eiqodreydm@6pag34zcnekp>
Date: Wed, 3 Sep 2025 22:03:39 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Tejun Heo <tj@...nel.org>
Cc: Yi Tao <escape@...ux.alibaba.com>, hannes@...xchg.org, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: replace global percpu_rwsem with
 signal_struct->group_rwsem when writing cgroup.procs/threads

On Wed, Sep 03, 2025 at 06:53:36AM -1000, Tejun Heo <tj@...nel.org> wrote:
> If you use CLONE_INTO_CGROUP, cgroup migration doesn't just become cold. It
> disappears completely and CLONE_INTO_CGROUP doesn't need any global locks
> from cgroup side.

CLONE_INTO_CGROUP uses cgroup_mutex and threadgroup rwsem like regular
migration, no? Its effect is atomicity wrt clone.
Or, Tejum, what do you mean that it disappears? (I think we cannot give
up cgroup_mutex as it ensures synchronization of possible parent's
migration.)

Michal

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