Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.35 as permitted sender) client-ip=23.128.96.35;
Date:   Wed, 1 Nov 2023 15:38:14 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Z qiang <qiang.zhang1211@gmail.com>
Cc:     "Paul E. McKenney" <paulmck@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Valentin Schneider <vschneid@redhat.com>,
        linux-kernel@vger.kernel.org, Phil Auld <pauld@redhat.com>,
        kernel test robot <oliver.sang@intel.com>,
        aubrey.li@linux.intel.com, yu.c.chen@intel.com,
        frederic@kernel.org, quic_neeraju@quicinc.com,
        joel@joelfernandes.org, josh@joshtriplett.org,
        boqun.feng@gmail.com, mathieu.desnoyers@efficios.com,
        jiangshanlai@gmail.com
Subject: Re: [PATCH] rcu: Break rcu_node_0 --> &rq->__lock order
Message-ID: <20231101143814.GL15024@noisy.programming.kicks-ass.net>
References: <20231031001418.274187-1-longman@redhat.com>
 <20231031085308.GB35651@noisy.programming.kicks-ass.net>
 <a46f5614-53ec-49fb-86d0-fa5aea4d0a42@paulmck-laptop>
 <20231031200228.GG15024@noisy.programming.kicks-ass.net>
 <CALm+0cWuZZLWkwMPS6n1YyTWzkex9=c1E9CB-m6e_F38MNLVqw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALm+0cWuZZLWkwMPS6n1YyTWzkex9=c1E9CB-m6e_F38MNLVqw@mail.gmail.com>
Precedence: bulk

On Wed, Nov 01, 2023 at 07:21:09PM +0800, Z qiang wrote:

> >  static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
> >  {
> >         unsigned long jtsq;
> > +       int ret = 0;
> >         struct rcu_node *rnp = rdp->mynode;
> >
> >         /*
> > @@ -847,8 +852,8 @@ static int rcu_implicit_dynticks_qs(stru
> >             (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
> >              rcu_state.cbovld)) {
> >                 WRITE_ONCE(rdp->rcu_urgent_qs, true);
> > -               resched_cpu(rdp->cpu);
> >                 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
> > +               ret = -1;
> >         }
> >
> 
> 
> Maybe some modifications are missing here:
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index aa4c808978b8..77e7a0dc722a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -867,8 +867,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
>         if (time_after(jiffies, rcu_state.jiffies_resched)) {
>                 if (time_after(jiffies,
>                                READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
> -                       resched_cpu(rdp->cpu);
>                         WRITE_ONCE(rdp->last_fqs_resched, jiffies);
> +                       ret = -1;
>                 }
>                 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
>                     !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
> 
> 

Bah, you're quite right, I missed that there were two sites calling
resched_cpu().

Paul, do you want a fixed up version or will you fold in the fix?