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Message-ID: <45e18c45-1c09-863a-65a0-3ae03ba4f859@quicinc.com>
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
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