linux-kernel - [PATCH 0/1] cgroup: avoid the unnecessary list_add(dying_tasks) in cgroup

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Message-ID: <20240617143129.GA10395@redhat.com>
Date: Mon, 17 Jun 2024 16:31:29 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Tejun Heo <tj@...nel.org>
Cc: Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/1] cgroup: avoid the unnecessary list_add(dying_tasks) in
 cgroup_exit()

Hello,

Sorry for delay and for confusing you in our previous discussion
here https://lore.kernel.org/all/20240610105028.GA21586@redhat.com/

No, cgroup_exit() can't rely on group_dead, this is racy.

And no, we can't shift css_set_skip_task_iters/etc from cgroup_release()
to cgroup_exit(), an execing sub-thread can change the group leader.

Let me at least send the simple patch which looks "obviously good" to me.

I would really like to remove the usage of signal->live in cgroup.c, but
so far I do not see a simple solution.

With or without this change cgroup.procs can be empty but cgroup.threads
is not. But at least the exiting sub-threads which have already passed
atomic_dec_and_test() should call cgroup_exit() "soon".

Oleg.