linux-kernel - Re: [PATCH RFC] rcu: torture: shorten the time between forward-progress tests

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Message-ID: <795ab1ed-de92-4f31-9483-b1800b597405@paulmck-laptop>
Date:   Wed, 23 Aug 2023 14:15:43 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     zhouzhouyi@...il.com
Cc:     rcu@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, lance@...osl.org
Subject: Re: [PATCH RFC] rcu: torture: shorten the time between
 forward-progress tests

On Tue, May 02, 2023 at 11:06:02PM +0800, zhouzhouyi@...il.com wrote:
> From: Zhouyi Zhou <zhouzhouyi@...il.com>
> 
> Currently, default time between rcu torture forward-progress tests is 60HZ,
> Under this configuration, false positive caused by __stack_chk_fail [1] is
> difficult to reproduce (needs average 5*420 seconds for SRCU-P),
> which means one has to invoke [2] 5 times in average to make [1] appear.
> 
> With time between rcu torture forward-progress tests be 1 HZ, above
> phenomenon will be reproduced within 3 minutes, which means we can
> reproduce [1] everytime we invoke [2].
> 
> Although [1] is a false positive, this change will make possible future
> true bugs easier to be discovered.            
>                    
> [1] Link: https://lore.kernel.org/lkml/CAABZP2yS5=ZUwEZQ7iHkV0wDm_HgO8K-TeAhyJrZhavzKDa44Q@mail.gmail.com/T/
> [2] tools/testing/selftests/rcutorture/bin/torture.sh
> 
> Tested in PPC VM of Opensource Lab of Oregon State Univerisity.
>         
> Signed-off-by: Zhouyi Zhou <zhouzhouyi@...il.com>        

Please accept my apologies for being ridiculously slow to reply!

In recent -rcu, module parameters such as this one that simply set a
value can be overridden on the command line.  So you could get the effect
(again, in recent kernels) in your testing by adding:

	--bootargs "rcutorture.fwd_progress_holdoff=1"

The reason that I am reluctant to accept this patch is that we sometimes
have trouble with this forward-progress testing exhausting memory, and
making in happen could therefore cause trouble with generic rcutorture
testing.

Or am I missing the point of this change?

							Thanx, Paul

> ---
>  tools/testing/selftests/rcutorture/configs/rcu/SRCU-N.boot  | 1 +
>  tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot  | 1 +
>  tools/testing/selftests/rcutorture/configs/rcu/TRACE02.boot | 1 +
>  tools/testing/selftests/rcutorture/configs/rcu/TREE02.boot  | 1 +
>  tools/testing/selftests/rcutorture/configs/rcu/TREE10.boot  | 1 +
>  5 files changed, 5 insertions(+)
> 
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N.boot b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N.boot
> index ce0694fd9b92..982582bff041 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N.boot
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-N.boot
> @@ -1,2 +1,3 @@
>  rcutorture.torture_type=srcu
>  rcutorture.fwd_progress=3
> +rcutorture.fwd_progress_holdoff=1
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot
> index 2db39f298d18..18f5d7361d8a 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/SRCU-P.boot
> @@ -1,4 +1,5 @@
>  rcutorture.torture_type=srcud
>  rcupdate.rcu_self_test=1
>  rcutorture.fwd_progress=3
> +rcutorture.fwd_progress_holdoff=1
>  srcutree.big_cpu_lim=5
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TRACE02.boot b/tools/testing/selftests/rcutorture/configs/rcu/TRACE02.boot
> index c70b5db6c2ae..b86bc7df7603 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/TRACE02.boot
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/TRACE02.boot
> @@ -1,2 +1,3 @@
>  rcutorture.torture_type=tasks-tracing
>  rcutorture.fwd_progress=2
> +rcutorture.fwd_progress_holdoff=1
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE02.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE02.boot
> index dd914fa8f690..933302f885df 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE02.boot
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE02.boot
> @@ -1 +1,2 @@
>  rcutorture.fwd_progress=2
> +rcutorture.fwd_progress_holdoff=1
> diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE10.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE10.boot
> index dd914fa8f690..933302f885df 100644
> --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE10.boot
> +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE10.boot
> @@ -1 +1,2 @@
>  rcutorture.fwd_progress=2
> +rcutorture.fwd_progress_holdoff=1
> -- 
> 2.34.1
>