linux-kernel - Re: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits with HZ/20

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Date:   Wed, 23 Aug 2023 14:07:55 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     linux-kernel@...r.kernel.org, Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        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
Subject: Re: [PATCH] rcutorture: Replace schedule_timeout*() 1 jiffie waits
 with HZ/20

On Wed, Aug 16, 2023 at 08:49:12PM +0000, Joel Fernandes (Google) wrote:
> In the past, we see that spinning on schedule_timeout* with a wait of 1
> jiffie can hang the kernel. See d52d3a2bf408 ("torture: Fix hang during
> kthread shutdown phase").
> 
> Recently again it showed up in torture's stutter code as well. The behavior is
> the the function may instantly return and never go to sleep preempting whatever
> was running under it.
> 
> To prevent future issues, apply the same fix mentioned in the above
> commit d52d3a2bf408 to more places.
> 
> I took care to only apply it to places where I thought it made sense.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>

Hearing no objections, I applied this for further review and testing.

In the future, should some of these become hrtimers?

						Thanx, Paul

> ---
>  kernel/rcu/rcutorture.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index 8dd52ea78b52..a31297f32a2a 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -1153,7 +1153,7 @@ static int rcu_torture_boost(void *arg)
>  				mutex_unlock(&boost_mutex);
>  				break;
>  			}
> -			schedule_timeout_uninterruptible(1);
> +			schedule_timeout_uninterruptible(HZ / 20);
>  		}
>  
>  		/* Go do the stutter. */
> @@ -1164,7 +1164,7 @@ checkwait:	if (stutter_wait("rcu_torture_boost"))
>  	/* Clean up and exit. */
>  	while (!kthread_should_stop()) {
>  		torture_shutdown_absorb("rcu_torture_boost");
> -		schedule_timeout_uninterruptible(1);
> +		schedule_timeout_uninterruptible(HZ / 20);
>  	}
>  	torture_kthread_stopping("rcu_torture_boost");
>  	return 0;
> @@ -1187,7 +1187,7 @@ rcu_torture_fqs(void *arg)
>  		fqs_resume_time = jiffies + fqs_stutter * HZ;
>  		while (time_before(jiffies, fqs_resume_time) &&
>  		       !kthread_should_stop()) {
> -			schedule_timeout_interruptible(1);
> +			schedule_timeout_interruptible(HZ / 20);
>  		}
>  		fqs_burst_remaining = fqs_duration;
>  		while (fqs_burst_remaining > 0 &&
> @@ -2903,7 +2903,7 @@ static int rcu_torture_fwd_prog(void *args)
>  			WRITE_ONCE(rcu_fwd_seq, rcu_fwd_seq + 1);
>  		} else {
>  			while (READ_ONCE(rcu_fwd_seq) == oldseq && !torture_must_stop())
> -				schedule_timeout_interruptible(1);
> +				schedule_timeout_interruptible(HZ / 20);
>  			oldseq = READ_ONCE(rcu_fwd_seq);
>  		}
>  		pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id);
> @@ -3204,7 +3204,7 @@ static int rcu_torture_read_exit_child(void *trsp_in)
>  	set_user_nice(current, MAX_NICE);
>  	// Minimize time between reading and exiting.
>  	while (!kthread_should_stop())
> -		schedule_timeout_uninterruptible(1);
> +		schedule_timeout_uninterruptible(HZ / 20);
>  	(void)rcu_torture_one_read(trsp, -1);
>  	return 0;
>  }
> @@ -3252,7 +3252,7 @@ static int rcu_torture_read_exit(void *unused)
>  	smp_mb(); // Store before wakeup.
>  	wake_up(&read_exit_wq);
>  	while (!torture_must_stop())
> -		schedule_timeout_uninterruptible(1);
> +		schedule_timeout_uninterruptible(HZ / 20);
>  	torture_kthread_stopping("rcu_torture_read_exit");
>  	return 0;
>  }
> -- 
> 2.41.0.694.ge786442a9b-goog
>