linux-kernel - Re: [PATCH 1/3] cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO

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Message-ID: <20230403165523.aphsec2epqi72k27@blackpad>
Date:   Mon, 3 Apr 2023 18:55:23 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Christian Brauner <brauner@...nel.org>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        gscrivan@...hat.com
Subject: Re: [PATCH 1/3] cgroup/cpuset: Make cpuset_fork() handle
 CLONE_INTO_CGROUP properly

On Fri, Mar 31, 2023 at 10:50:43AM -0400, Waiman Long <longman@...hat.com> wrote:
> By default, the clone(2) syscall spawn a child process into the same
> cgroup as its parent. With the use of the CLONE_INTO_CGROUP flag
> introduced by commit ef2c41cf38a7 ("clone3: allow spawning processes
> into cgroups"), the child will be spawned into a different cgroup which
> is somewhat similar to writing the child's tid into "cgroup.threads".
> 
> The current cpuset_fork() method does not properly handle the
> CLONE_INTO_CGROUP case where the cpuset of the child may be different
> from that of its parent.  Update the cpuset_fork() method to treat the
> CLONE_INTO_CGROUP case similar to cpuset_attach().

Should .can_fork=cpuset_can_fork in analogy to cpuset_can_attach be also
devised? (Sorry if I missed that in the previous discussion.)

> 
> Since the newly cloned task has not been running yet, its actual
> memory usage isn't known. So it is not necessary to make change to mm
> in cpuset_fork().
> 
> Fixes: ef2c41cf38a7 ("clone3: allow spawning processes into cgroups")
> Signed-off-by: Waiman Long <longman@...hat.com>

Thanks,
Michal

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