linux-kernel - Re: Prototype patch to avoid TREE07 rcu_torture

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Message-ID: <127b057c-446e-4b3f-bb04-d1c4efdded0f@paulmck-laptop>
Date: Sat, 6 Jan 2024 16:49:49 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: linux-kernel@...r.kernel.org
Subject: Re: Prototype patch to avoid TREE07 rcu_torture_writer() stalls

On Sat, Jan 06, 2024 at 11:36:03PM +0100, Frederic Weisbecker wrote:
> Le Sat, Jan 06, 2024 at 06:55:14AM -0800, Paul E. McKenney a écrit :
> > > Is this related?
> > > 
> > > But then the system picks itself up, dusts itself off, and goes along
> > > as if nothing had happened.
> > > 
> > > Maybe a long-running IRQ, NMI, or SMI?
> > 
> > Or, based on a recent bug chase of another type, high contention on
> > an IRQ-disabled spinlock?
> 
> Before checking the guest's dmesg, I should probably have checked the host's.
> It seems to report some softlockups, perhaps due to too many instances
> in parallel where memory is not that generous.

That would do it!

> Let me try to run as much time (250 hours) but with fewer instances in
> parallel.

I just today saw an extended stall on one instance of TREE03, also
RCU grace-period kthread starvation.  But this was in -next, which
is also having other yet-as-unanalyzed issues.

							Thanx, Paul