linux-kernel - Re: [PATCH] cgroup/cpuset: update parent subparts cpumask while holding css refcnt

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Message-ID: <ag6ed2ebb3azrienshnvn775ejp6jsftx66we7mwcavv74q4s7@xm5djhor7bjl>
Date:   Mon, 10 Jul 2023 17:51:24 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Miaohe Lin <linmiaohe@...wei.com>, tj@...nel.org,
        hannes@...xchg.org, lizefan.x@...edance.com,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup/cpuset: update parent subparts cpumask while
 holding css refcnt

On Mon, Jul 10, 2023 at 11:40:36AM -0400, Waiman Long <longman@...hat.com> wrote:
> I believe the primary reason is because update_parent_subparts_cpumask() can
> potential run for quite a while. So we don't want to hold the rcu_read_lock
> for too long.

But holding cpuset_mutex is even worse than rcu_read_lock()? IOW is the
relieve with this reason worth it?

> There may also be a potential that schedule() may be called.

Do you mean the spinlocks with PREEMPT_RT or anything else? (That seems
like the actual reason IIUC.)

Thanks,
Michal

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