linux-kernel - Re: [PATCH 02/10] workqueue: use cpu_possible_mask instead of cpu_active

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Message-ID: <20201215084021.GQ3092@hirez.programming.kicks-ass.net>
Date:   Tue, 15 Dec 2020 09:40:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Tejun Heo <tj@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 02/10] workqueue: use cpu_possible_mask instead of
 cpu_active_mask to break affinity

On Mon, Dec 14, 2020 at 06:25:34PM +0100, Peter Zijlstra wrote:
> On Mon, Dec 14, 2020 at 11:54:49PM +0800, Lai Jiangshan wrote:
> > From: Lai Jiangshan <laijs@...ux.alibaba.com>
> > 
> > There might be other CPU online. The workers losing binding on its CPU
> > should have chance to work on those later onlined CPUs.
> > 
> > Fixes: 06249738a41a ("workqueue: Manually break affinity on hotplug")
> > Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> > ---
> >  kernel/workqueue.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > index aba71ab359dd..1f5b8385c0cf 100644
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -4909,8 +4909,9 @@ static void unbind_workers(int cpu)
> >  
> >  		raw_spin_unlock_irq(&pool->lock);
> >  
> > +		/* don't rely on the scheduler to force break affinity for us. */
> >  		for_each_pool_worker(worker, pool)
> > -			WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_active_mask) < 0);
> > +			WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
> 
> Please explain this one.. it's not making sense. Also the Changelog
> doesn't seem remotely related to the actual change.
> 
> Afaict this is actively wrong.

I think I was too tired, I see what you're doing now and it should work
fine, I still think the changelog could use help though.