linux-kernel - Re: [PATCH 1/1] cgroup: Fix race condition at rebind

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Date:   Tue, 23 Aug 2022 13:03:58 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Jing-Ting Wu <Jing-Ting.Wu@...iatek.com>,
        Michal Koutný <mkoutny@...e.com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthias Brugger <matthias.bgg@...il.com>
CC:     <Jonathan.JMChen@...iatek.com>, <Lixiong.Liu@...iatek.com>,
        <wsd_upstream@...iatek.com>, <Wenju.Xu@...iatek.com>,
        <cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH 1/1] cgroup: Fix race condition at rebind_subsystems()



On 8/23/2022 11:11 AM, Jing-Ting Wu wrote:
> Root cause:
> The rebind_subsystems() is no lock held when move css object from A
> list to B list,then let B's head be treated as css node at
> list_for_each_entry_rcu().
> 
> Solution:
> Add grace period before invalidating the removed rstat_css_node.
> 
> Reported-by: Jing-Ting Wu <jing-ting.wu@...iatek.com>
> Suggested-by: Michal Koutný <mkoutny@...e.com>
> Signed-off-by: Jing-Ting Wu <jing-ting.wu@...iatek.com>
> Tested-by: Jing-Ting Wu <jing-ting.wu@...iatek.com>
> Link: https://lore.kernel.org/linux-arm-kernel/d8f0bc5e2fb6ed259f9334c83279b4c011283c41.camel@mediatek.com/T/
> ---
>   kernel/cgroup/cgroup.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index ffaccd6373f1..0d0c959966ed 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -1820,6 +1820,7 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
>   
>   		if (ss->css_rstat_flush) {
>   			list_del_rcu(&css->rstat_css_node);
> +			synchronize_rcu();
>   			list_add_rcu(&css->rstat_css_node,
>   				     &dcgrp->rstat_css_list);
>   		}

Good catch.

Acked-by: Mukesh Ojha <quic_mojha@...cinc.com>

-Mukesh