linux-kernel - Re: [tip:timers/urgent] [timers/migration] 8cdb61838e: WARNING:at_kernel/time/timer_migration.c:#tmigr_connect_child

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Message-ID: <75673424-69b3-4774-a647-d41a259f9a55@paulmck-laptop>
Date: Tue, 16 Jul 2024 06:41:47 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
	lkp@...el.com, linux-kernel@...r.kernel.org, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [tip:timers/urgent] [timers/migration]  8cdb61838e:
 WARNING:at_kernel/time/timer_migration.c:#tmigr_connect_child_parent

On Tue, Jul 16, 2024 at 09:36:47AM +0200, Anna-Maria Behnsen wrote:
> Hi Paul,
> 
> "Paul E. McKenney" <paulmck@...nel.org> writes:
> 
> > On Wed, Jul 10, 2024 at 04:37:00PM +0800, kernel test robot wrote:
> >> 
> >> 
> >> Hello,
> >> 
> >> kernel test robot noticed "WARNING:at_kernel/time/timer_migration.c:#tmigr_connect_child_parent" on:
> >> 
> >> commit: 8cdb61838ee5c63556773ea2eed24deab6b15257 ("timers/migration: Move hierarchy setup into cpuhotplug prepare callback")
> >> https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git timers/urgent
> >
> > For whatever it is worth, I am also seeing this on refscale runs on
> > recent -next.
> >
> > The reproducer is to clone perfbook [1] in your ~/git directory
> > (as in ~/git/perfboot), then run this from your Linux source tree,
> > preferably on a system with few CPUs:
> >
> > bash ~/git/perfbook/CodeSamples/defer/rcuscale.sh
> >
> > The output will have "FAIL" in it, which indicates that the corresponding
> > guest OS splatted.  If it would be useful, I would be happy to produce
> > a one-liner that runs the guest OS only once and leaves the console
> > output around.  Otherwise, I will continue being lazy.  ;-)
> 
> Thanks for the report. I found the root cause for it and I am working on
> a fix as the commit which triggers the warning also has another
> problem... And I already requested to drop the tip timers/urgent patches
> (at least my patches).
> 
> So, enjoy being lazy!

Glad that you are on it, thank you!

And yes, the option of being lazy seems to be increasingly attractive
as the years rush by...  ;-)

							Thanx, Paul