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Message-ID: <9244d968-b25a-066f-2ff3-1281bf03983e@redhat.com>
Date:   Sat, 1 Jul 2023 19:38:57 -0400
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Subject: Re: [PATCH] cgroup/cpuset: update parent subparts cpumask while
 holding css refcnt
Content-Language: en-US
To:     Miaohe Lin <linmiaohe@huawei.com>, tj@kernel.org,
        hannes@cmpxchg.org, lizefan.x@bytedance.com
Cc:     cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20230701065049.1758266-1-linmiaohe@huawei.com>
From:   Waiman Long <longman@redhat.com>
In-Reply-To: <20230701065049.1758266-1-linmiaohe@huawei.com>
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On 7/1/23 02:50, Miaohe Lin wrote:
> update_parent_subparts_cpumask() is called outside RCU read-side critical
> section without holding extra css refcnt of cp. In theroy, cp could be
> freed at any time. Holding extra css refcnt to ensure cp is valid while
> updating parent subparts cpumask.
>
> Fixes: d7c8142d5a55 ("cgroup/cpuset: Make partition invalid if cpumask change violates exclusivity rule")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
>   kernel/cgroup/cpuset.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 58e6f18f01c1..632a9986d5de 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1806,9 +1806,12 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   		cpuset_for_each_child(cp, css, parent)
>   			if (is_partition_valid(cp) &&
>   			    cpumask_intersects(trialcs->cpus_allowed, cp->cpus_allowed)) {
> +				if (!css_tryget_online(&cp->css))
> +					continue;
>   				rcu_read_unlock();
>   				update_parent_subparts_cpumask(cp, partcmd_invalidate, NULL, &tmp);
>   				rcu_read_lock();
> +				css_put(&cp->css);
>   			}
>   		rcu_read_unlock();
>   		retval = 0;

Thanks for finding that. It looks good to me.

Reviewed-by: Waiman Long <longman@redhat.com>