linux-kernel - Re: [PATCH v10 1/3] smpboot: allow excluding cpus from the smpboot threads

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Message-ID: <20150603023457.GH5847@redhat.com>
Date:	Tue, 2 Jun 2015 22:34:57 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Jones <drjones@...hat.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ben Zhang <benzh@...omium.org>,
	Christoph Lameter <cl@...ux.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	linux-doc@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v10 1/3] smpboot: allow excluding cpus from the smpboot
 threads

On Mon, May 04, 2015 at 06:06:24PM -0400, Chris Metcalf wrote:
> On 5/1/2015 5:23 PM, Frederic Weisbecker wrote:
> >On Fri, May 01, 2015 at 03:57:51PM -0400, Chris Metcalf wrote:
> >
> >>For example, booting with only cpu 0 as a housekeeping core (and
> >>therefore all watchdogs 1-35 on my 36-core tilegx are parked), and
> >>immediately doing "echo 0 > /proc/sys/kernel/watchdog", I see
> >>(via SysRq ^O-l) the first parked watchdog, on cpu 1, hung with:
> >>
> >>   frame 0: 0xfffffff7000f2928 lock_hrtimer_base+0xb8/0xc0
> >>   frame 1: 0xfffffff7000f2a28 hrtimer_try_to_cancel+0x40/0x170
> >>   frame 2: 0xfffffff7000f2a28 hrtimer_try_to_cancel+0x40/0x170
> >>   frame 3: 0xfffffff7000f2b98 hrtimer_cancel+0x40/0x68
> >>   frame 4: 0xfffffff70014cce0 watchdog_disable+0x50/0x70
> >>   frame 5: 0xfffffff70008c2d0 smpboot_thread_fn+0x350/0x438
> >>   frame 6: 0xfffffff700084b28 kthread+0x160/0x178
> >Have you tried to do that before your patchset?
> 
> Yes, it works fine.  It requires the presence of the parked threads to trigger the issue.
> 
> >>The config does not have NO_HZ_FULL_ALL or NO_HZ_FULL_SYSIDLE
> >>set, and does have RCU_FAST_NO_HZ and RCU_NOCB_CPU_ALL.
> >>
> >>I don't really know how to start debugging this, but I do know that
> >>unparking the threads first avoids the issue :-)
> >Do you have CONFIG_PROVE_LOCKING=y ?
> 
> There seems to be some skew between the community version, which is throwing a
> bunch of errors when I enable PROVE_LOCKING, and our internal version where some
> things are not yet upstreamed but PROVE_LOCKING works :-)
> 
> I'll try to set aside some time to reconcile the two to figure it out.

Hi Chris,

I was digging this thread back up and wondered what happened.  It seems like
a v11 was going to materialize?

Cheers,
Don
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