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Date: Tue, 2 Jun 2015 22:34:57 -0400
From: Don Zickus <dzickus@redhat.com>
To: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>, Andrew Jones <drjones@redhat.com>,
        Ulrich Obergfell <uobergfe@redhat.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v10 1/3] smpboot: allow excluding cpus from the smpboot
 threads
Message-ID: <20150603023457.GH5847@redhat.com>
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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