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Message-ID: <063a2eba-6b5e-40bc-afd4-7d26f12762e4@paulmck-laptop>
Date: Wed, 2 Aug 2023 08:05:08 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Roy Hopkins <rhopkins@...e.de>
Cc: Guenter Roeck <linux@...ck-us.net>,
Peter Zijlstra <peterz@...radead.org>,
Joel Fernandes <joel@...lfernandes.org>,
Pavel Machek <pavel@...x.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, patches@...ts.linux.dev,
linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
akpm@...ux-foundation.org, shuah@...nel.org, patches@...nelci.org,
lkft-triage@...ts.linaro.org, jonathanh@...dia.com,
f.fainelli@...il.com, sudipm.mukherjee@...il.com,
srw@...dewatkins.net, rwarsow@....de, conor@...nel.org,
rcu@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: scheduler problems in -next (was: Re: [PATCH 6.4 000/227]
6.4.7-rc1 review)
On Wed, Aug 02, 2023 at 02:57:56PM +0100, Roy Hopkins wrote:
> On Tue, 2023-08-01 at 12:11 -0700, Paul E. McKenney wrote:
> > On Tue, Aug 01, 2023 at 10:32:45AM -0700, Guenter Roeck wrote:
> >
> >
> > Please see below for my preferred fix. Does this work for you guys?
> >
> > Back to figuring out why recent kernels occasionally to blow up all
> > rcutorture guest OSes...
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> > index 7294be62727b..2d5b8385c357 100644
> > --- a/kernel/rcu/tasks.h
> > +++ b/kernel/rcu/tasks.h
> > @@ -570,10 +570,12 @@ static void rcu_tasks_one_gp(struct rcu_tasks *rtp, bool midboot)
> > if (unlikely(midboot)) {
> > needgpcb = 0x2;
> > } else {
> > + mutex_unlock(&rtp->tasks_gp_mutex);
> > set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
> > rcuwait_wait_event(&rtp->cbs_wait,
> > (needgpcb = rcu_tasks_need_gpcb(rtp)),
> > TASK_IDLE);
> > + mutex_lock(&rtp->tasks_gp_mutex);
> > }
> >
> > if (needgpcb & 0x2) {
>
> Your preferred fix looks good to me.
>
> With the original code I can quite easily reproduce the problem on my
> system every 10 reboots or so. With your fix in place the problem no
> longer occurs.
Very good, thank you! May I add your Tested-by?
Thanx, Paul
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