netdev - Re: [PATCH v2] wireguard: queueing: simplify wg_cpumask_next

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Message-ID: <CAHmME9qLiyWEhU6DrK+QWu5wo7Hmq-YjftmqGagCmEp3bjy4DQ@mail.gmail.com>
Date: Mon, 30 Jun 2025 20:20:45 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Tejun Heo <tj@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, wireguard@...ts.zx2c4.com, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] wireguard: queueing: simplify wg_cpumask_next_online()

On Mon, Jun 30, 2025 at 8:15 PM Yury Norov <yury.norov@...il.com> wrote:
>
> > > > From fbdce972342437fb12703cae0c3a4f8f9e218a1b Mon Sep 17 00:00:00 2001
> > > > From: Yury Norov (NVIDIA) <yury.norov@...il.com>
> > > > Date: Mon, 30 Jun 2025 13:47:49 -0400
> > > > Subject: [PATCH] workqueue: relax condition in __queue_work()
> > > >
> > > > Some cpumask search functions may return a number greater than
> > > > nr_cpu_ids when nothing is found. Adjust __queue_work() to it.
> > > >
> > > > Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
> > > > ---
> > > >  kernel/workqueue.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> > > > index 9f9148075828..abacfe157fe6 100644
> > > > --- a/kernel/workqueue.c
> > > > +++ b/kernel/workqueue.c
> > > > @@ -2261,7 +2261,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
> > > >         rcu_read_lock();
> > > >  retry:
> > > >         /* pwq which will be used unless @work is executing elsewhere */
> > > > -       if (req_cpu == WORK_CPU_UNBOUND) {
> > > > +       if (req_cpu >= WORK_CPU_UNBOUND) {
> > > >                 if (wq->flags & WQ_UNBOUND)
> > > >                         cpu = wq_select_unbound_cpu(raw_smp_processor_id());
> > > >                 else
> > > >
> > >
> > > Seems reasonable to me... Maybe submit this to Tejun and CC me?
> >
> > Sure, no problem.
>
> Hmm... So, actually WORK_CPU_UNBOUND is NR_CPUS, which is not the same
> as nr_cpu_ids. For example, on my Ubuntu machine, the CONFIG_NR_CPUS
> is 8192, and nr_cpu_ids is 8.
>
> So, for the wg_cpumask_next_online() to work properly, we need to
> return the WORK_CPU_UNBOUND in case of nothing is found.

Or just try again? Could just make your if into a while.