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

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Message-ID: <aXizUsfywjtIIN50@localhost.localdomain>
Date: Tue, 27 Jan 2026 13:45:06 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Michal Hocko <mhocko@...e.com>
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

Le Mon, Jan 26, 2026 at 05:41:38PM +0100, Michal Hocko a écrit :
> 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?

This is what guard(rcu)() does, right?
Or am I missing something?

Thanks.

-- 
Frederic Weisbecker
SUSE Labs