linux-kernel - Re: [PATCH-rcu] rcu-tasks: Use delayed_work to delay rcu_tasks_verify_self

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Date:   Tue, 14 Jun 2022 12:00:44 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        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>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>
Subject: Re: [PATCH-rcu] rcu-tasks: Use delayed_work to delay
 rcu_tasks_verify_self_tests()

On Tue, Jun 14, 2022 at 08:06:20AM -0400, Waiman Long wrote:
> Commit 2585014188d5 ("rcu-tasks: Be more patient for RCU Tasks
> boot-time testing") fixes false positive rcu_tasks verification check
> failure by repeating the test once every second until timeout using
> schedule_timeout_uninterruptible().
> 
> Since rcu_tasks_verify_selft_tests() is called from do_initcalls()
> as a late_initcall, this has the undesirable side effect of perhaps
> delaying other late_initcall's queued after it by a second or more.
> Fix this by using delayed_work to repeat the verification check instead.
> 
> Fixes: 2585014188d5 ("rcu-tasks: Be more patient for RCU Tasks boot-time testing")
> Signed-off-by: Waiman Long <longman@...hat.com>

Applied, thank you!

							Thanx, Paul

> ---
>  kernel/rcu/tasks.h | 35 ++++++++++++++++++++++++++++++++---
>  1 file changed, 32 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index fcbd0ec33c86..e151cd5ae2bc 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -1832,6 +1832,11 @@ static void rcu_tasks_initiate_self_tests(void)
>  #endif
>  }
>  
> +/*
> + * Return:  0 - test passed
> + *	    1 - test failed, but have not timed out yet
> + *	   -1 - test failed and timed out
> + */
>  static int rcu_tasks_verify_self_tests(void)
>  {
>  	int ret = 0;
> @@ -1847,16 +1852,40 @@ static int rcu_tasks_verify_self_tests(void)
>  				ret = -1;
>  				break;
>  			}
> -			schedule_timeout_uninterruptible(1);
> +			ret = 1;
> +			break;
>  		}
>  	}
>  
> -	if (ret)
> +	if (ret < 0)
>  		WARN_ON(1);
>  
>  	return ret;
>  }
> -late_initcall(rcu_tasks_verify_self_tests);
> +
> +/*
> + * Repeat the rcu_tasks_verify_self_tests() call once every second until the
> + * test passes or has timed out.
> + */
> +static struct delayed_work rcu_tasks_verify_work;
> +static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused)
> +{
> +	int ret = rcu_tasks_verify_self_tests();
> +
> +	if (ret <= 0)
> +		return;
> +
> +	/* Test fails but not timed out yet, reschedule another check */
> +	schedule_delayed_work(&rcu_tasks_verify_work, HZ);
> +}
> +
> +static int rcu_tasks_verify_schedule_work(void)
> +{
> +	INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn);
> +	rcu_tasks_verify_work_fn(NULL);
> +	return 0;
> +}
> +late_initcall(rcu_tasks_verify_schedule_work);
>  #else /* #ifdef CONFIG_PROVE_RCU */
>  static void rcu_tasks_initiate_self_tests(void) { }
>  #endif /* #else #ifdef CONFIG_PROVE_RCU */
> -- 
> 2.31.1
>