linux-kernel - Re: [PATCH 2/2] rcu-tasks: add RCU-tasks self tests

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Date:   Fri, 12 Feb 2021 22:12:07 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>
Cc:     "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, RCU <rcu@...r.kernel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Axtens <dja@...ens.net>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>
Subject: Re: [PATCH 2/2] rcu-tasks: add RCU-tasks self tests

On Fri, Feb 12, 2021 at 08:20:59PM +0100, Sebastian Andrzej Siewior wrote:
> On 2020-12-09 21:27:32 [+0100], Uladzislau Rezki (Sony) wrote:
> > Add self tests for checking of RCU-tasks API functionality.
> > It covers:
> >     - wait API functions;
> >     - invoking/completion call_rcu_tasks*().
> > 
> > Self-tests are run when CONFIG_PROVE_RCU kernel parameter is set.
> 
> I just bisected to this commit. By booting with `threadirqs' I end up
> with:
> [    0.176533] Running RCU-tasks wait API self tests
> 
> No stall warning or so.
> It boots again with:
> 
> diff --git a/init/main.c b/init/main.c
> --- a/init/main.c
> +++ b/init/main.c
> @@ -1489,6 +1489,7 @@ void __init console_on_rootfs(void)
>  	fput(file);
>  }
>  
> +void rcu_tasks_initiate_self_tests(void);
>  static noinline void __init kernel_init_freeable(void)
>  {
>  	/*
> @@ -1514,6 +1515,7 @@ static noinline void __init kernel_init_freeable(void)
>  
>  	rcu_init_tasks_generic();
>  	do_pre_smp_initcalls();
> +	rcu_tasks_initiate_self_tests();
>  	lockup_detector_init();
>  
>  	smp_init();
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -1266,7 +1266,7 @@ static void test_rcu_tasks_callback(struct rcu_head *rhp)
>  	rttd->notrun = true;
>  }
>  
> -static void rcu_tasks_initiate_self_tests(void)
> +void rcu_tasks_initiate_self_tests(void)
>  {
>  	pr_info("Running RCU-tasks wait API self tests\n");
>  #ifdef CONFIG_TASKS_RCU
> @@ -1322,7 +1322,6 @@ void __init rcu_init_tasks_generic(void)
>  #endif
>  
>  	// Run the self-tests.
> -	rcu_tasks_initiate_self_tests();
>  }
>  
>  #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
> 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> 
> Sebastian
>
We should be able to use call_rcu_tasks() in the *initcall() callbacks.
The problem is that, ksoftirqd threads are not spawned by the time when
an rcu_init_tasks_generic() is invoked:

diff --git a/init/main.c b/init/main.c
index c68d784376ca..e6106bb12b2d 100644
--- a/init/main.c
+++ b/init/main.c
@@ -954,7 +954,6 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
 	rcu_init_nohz();
 	init_timers();
 	hrtimers_init();
-	softirq_init();
 	timekeeping_init();
 
 	/*
@@ -1512,6 +1511,7 @@ static noinline void __init kernel_init_freeable(void)
 
 	init_mm_internals();
 
+	softirq_init();
 	rcu_init_tasks_generic();
 	do_pre_smp_initcalls();
 	lockup_detector_init();
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 9d71046ea247..cafa55c496d0 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -630,6 +630,7 @@ void __init softirq_init(void)
 			&per_cpu(tasklet_hi_vec, cpu).head;
 	}
 
+	spawn_ksoftirqd();
 	open_softirq(TASKLET_SOFTIRQ, tasklet_action);
 	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 }
@@ -732,7 +733,6 @@ static __init int spawn_ksoftirqd(void)
 
 	return 0;
 }
-early_initcall(spawn_ksoftirqd);
 
 /*
  * [ These __weak aliases are kept in a separate compilation unit, so that

Any thoughts?

--
Vlad Rezki