linux-kernel - Re: [PATCH] rcutorture: Avoid soft lockup during cpu stall

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Date:   Tue, 9 Nov 2021 12:37:15 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     wander@...hat.com
Cc:     Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        "open list:TORTURE-TEST MODULES" <linux-kernel@...r.kernel.org>,
        "open list:READ-COPY UPDATE (RCU)" <rcu@...r.kernel.org>
Subject: Re: [PATCH] rcutorture: Avoid soft lockup during cpu stall

On Tue, Nov 09, 2021 at 02:46:02PM -0300, wander@...hat.com wrote:
> From: Wander Lairson Costa <wander@...hat.com>
> 
> If we use the module stall_cpu option, we may get a soft lockup warning
> if we also don't pass the stall_cpu_block option.
> 
> We introduce the stall_no_softlockup option to avoid a soft lockup on
> cpu stall even if we don't use the stall_cpu_block option.
> 
> Signed-off-by: Wander Lairson Costa <wander@...hat.com>

This looks plausible to me, though it would be good to hear others'
thoughts.  In the meantime, could you please forward-port this to
the "dev" branch of the -rcu tree?

https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html

							Thanx, Paul

> ---
>  kernel/rcu/rcutorture.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 40ef5417d954..0a2a9a6533d1 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -10,6 +10,7 @@
>   * See also:  Documentation/RCU/torture.rst
>   */
>  
> +#include "linux/nmi.h"
>  #define pr_fmt(fmt) fmt
>  
>  #include <linux/types.h>
> @@ -109,6 +110,8 @@ torture_param(int, shutdown_secs, 0, "Shutdown time (s), <= zero to disable.");
>  torture_param(int, stall_cpu, 0, "Stall duration (s), zero to disable.");
>  torture_param(int, stall_cpu_holdoff, 10,
>  	     "Time to wait before starting stall (s).");
> +torture_param(bool, stall_no_softlockup, false,
> +	     "Avoid softlockup warning during cpu stall.");
>  torture_param(int, stall_cpu_irqsoff, 0, "Disable interrupts while stalling.");
>  torture_param(int, stall_cpu_block, 0, "Sleep while stalling.");
>  torture_param(int, stall_gp_kthread, 0,
> @@ -2024,6 +2027,8 @@ static int rcu_torture_stall(void *args)
>  				    stop_at))
>  			if (stall_cpu_block)
>  				schedule_timeout_uninterruptible(HZ);
> +			else if (stall_no_softlockup)
> +				touch_softlockup_watchdog();
>  		if (stall_cpu_irqsoff)
>  			local_irq_enable();
>  		else if (!stall_cpu_block)
> -- 
> 2.27.0
>