linux-kernel - Re: [PATCH 2/2] rcu: Don't dump the stalled CPU on where RCU GP kthread last ran twice

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Message-ID: <39430021-dc0d-4abd-8266-642e4e2dc7df@paulmck-laptop>
Date:   Mon, 10 Jul 2023 12:05:58 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rcu: Don't dump the stalled CPU on where RCU GP
 kthread last ran twice

On Wed, Jul 05, 2023 at 03:30:20PM +0800, Zhen Lei wrote:
> The stacks of all stalled CPUs will be dumped. If the CPU on where RCU GP
> kthread last ran is stalled, its stack does not need to be dumped again.
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>

This one looks good.  Please feel free to rebase it before 1/2 and repost.

							Thanx, Paul

> ---
>  kernel/rcu/tree_stall.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index dcfaa3d5db2cbc7..cc884cd49e026a3 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -534,12 +534,14 @@ static void rcu_check_gp_kthread_starvation(void)
>  		       data_race(READ_ONCE(rcu_state.gp_state)),
>  		       gpk ? data_race(READ_ONCE(gpk->__state)) : ~0, cpu);
>  		if (gpk) {
> +			struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> +
>  			pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name);
>  			pr_err("RCU grace-period kthread stack dump:\n");
>  			sched_show_task(gpk);
>  			if (cpu_is_offline(cpu)) {
>  				pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu);
> -			} else  {
> +			} else if (!(data_race(READ_ONCE(rdp->mynode->qsmask)) & rdp->grpmask)) {
>  				pr_err("Stack dump where RCU GP kthread last ran:\n");
>  				dump_cpu_task(cpu);
>  			}
> -- 
> 2.25.1
>