netdev - Re: [PATCH 03/33] memcg: Prepare to protect against concurrent isolated cpuset change

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Message-ID: <aXeZQoSHJ9QX7B6W@tiehlicka>
Date: Mon, 26 Jan 2026 17:41:38 +0100
From: Michal Hocko <mhocko@...e.com>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Michal Koutný <mkoutny@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
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Subject: Re: [PATCH 03/33] memcg: Prepare to protect against concurrent
 isolated cpuset change

On Sun 25-01-26 23:45:10, Frederic Weisbecker wrote:
> The HK_TYPE_DOMAIN housekeeping cpumask will soon be made modifiable at
> runtime. In order to synchronize against memcg workqueue to make sure
> that no asynchronous draining is pending or executing on a newly made
> isolated CPU, target and queue a drain work under the same RCU critical
> section.
> 
> Whenever housekeeping will update the HK_TYPE_DOMAIN cpumask, a memcg
> workqueue flush will also be issued in a further change to make sure
> that no work remains pending after a CPU has been made isolated.
> 
> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> ---
>  mm/memcontrol.c | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index be810c1fbfc3..2289a0299331 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2003,6 +2003,19 @@ static bool is_memcg_drain_needed(struct memcg_stock_pcp *stock,
>  	return flush;
>  }
>  
> +static void schedule_drain_work(int cpu, struct work_struct *work)
> +{
> +	/*
> +	 * Protect housekeeping cpumask read and work enqueue together
> +	 * in the same RCU critical section so that later cpuset isolated
> +	 * partition update only need to wait for an RCU GP and flush the
> +	 * pending work on newly isolated CPUs.
> +	 */
> +	guard(rcu)();
> +	if (!cpu_is_isolated(cpu))
> +		schedule_work_on(cpu, work);

Shouldn't this in the guarded rcu section?
-- 
Michal Hocko
SUSE Labs