Re: [PATCH v2 2/3] clone3: allow spawning processes into cgroups

From: "Michal Koutný" <mkoutny@suse.com>
To: Christian Brauner <christian.brauner@ubuntu.com>
Cc: linux-api@vger.kernel.org, linux-kernel@vger.kernel.org,
	Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Li Zefan <lizefan@huawei.com>,
	Peter Zijlstra <peterz@infradead.org>,
	cgroups@vger.kernel.org
Subject: Re: [PATCH v2 2/3] clone3: allow spawning processes into cgroups
Date: Wed, 8 Jan 2020 17:01:02 +0100	[thread overview]
Message-ID: <20200108160102.GA17415@blackbody.suse.cz> (raw)
In-Reply-To: <20191223061504.28716-3-christian.brauner@ubuntu.com>

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On Mon, Dec 23, 2019 at 07:15:03AM +0100, Christian Brauner <christian.brauner@ubuntu.com> wrote:
> This adds support for creating a process in a different cgroup than its
> parent.
Binding fork and migration together looks useful.

> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -5882,21 +5882,176 @@ void cgroup_fork(struct task_struct *child)
>  	INIT_LIST_HEAD(&child->cg_list);
Just a nitpick, I noticed the comment for cgroup_fork should be updated
too (generic migration happens in cgroup_post_fork).

> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> [...]
> @@ -2279,8 +2278,7 @@ static __latent_entropy struct task_struct *copy_process(
>  	write_unlock_irq(&tasklist_lock);
>  
>  	proc_fork_connector(p);
> -	cgroup_post_fork(p);
> -	cgroup_threadgroup_change_end(current);
> +	cgroup_post_fork(current, p, args);
I can see that when CLONE_INTO_CGROUP | CLONE_NEWCGROUP is passed, then
the child's cgroup NS will be rooted at parent's css set
(copy_namespaces precedes cgroup_post_fork).

Wouldn't it make better sense if this flags combination resulted in
child's NS rooted in its css set?

Michal

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