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

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Message-ID: <CAABZP2zfSmeLO=DRTKP7wPg2zFc4a2AOx31oWTK-xLubqYvS0g@mail.gmail.com>
Date:   Thu, 24 Aug 2023 10:29:49 +0800
From:   Zhouyi Zhou <zhouzhouyi@...il.com>
To:     paulmck@...nel.org
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 Thu, Aug 24, 2023 at 5:15 AM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> 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!
Never mind. I have made a lot of self improvement during the study of
RCU and RCU torture and your book ;-)
>
> 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.
Agree, false positives can disrupt our judgement in many cases.

Thanx Zhouyi
>
> 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
> >