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Date:   Wed, 2 Aug 2023 08:05:08 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Roy Hopkins <rhopkins@suse.de>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Pavel Machek <pavel@denx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, patches@lists.linux.dev,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        akpm@linux-foundation.org, shuah@kernel.org, patches@kernelci.org,
        lkft-triage@lists.linaro.org, jonathanh@nvidia.com,
        f.fainelli@gmail.com, sudipm.mukherjee@gmail.com,
        srw@sladewatkins.net, rwarsow@gmx.de, conor@kernel.org,
        rcu@vger.kernel.org, Ingo Molnar <mingo@kernel.org>
Subject: Re: scheduler problems in -next (was: Re: [PATCH 6.4 000/227]
 6.4.7-rc1 review)
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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