linux-kernel - Re: Bisected oops regression between v3.7-rc8 and v3.7: nmi

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Date:	Sun, 16 Dec 2012 20:41:32 +0100
From:	Maciej Rutecki <maciej.rutecki@...il.com>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	linux-kernel@...r.kernel.org,
	Norbert Warmuth <nwarmuth@...nline.de>,
	Joseph Salisbury <joseph.salisbury@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Bisected oops regression between v3.7-rc8 and v3.7: nmi_watchdog

On piątek, 14 grudnia 2012 o 10:33:33 Bjørn Mork wrote:
> Hello,
> 
> I was a bit surprised by v3.7 hanging "all the time", usually just
> freezing but sometimes with a stack dump pointing to timerqueue_del
> calling rb_erase and oopsing there. Of course I could never make it dump
> anything when prepared to capture it via netconsole, so the best I have
> is this picture: http://www.mork.no/~bjorn/20121213_203557.jpg
> 
> I discovered that the freeze was related to plugging AC power and
> started bisecting from v3.7-rc3, which I had been running for quite a
> while and therefore was confident did not have this problem.  The bisect
> log ended up as this:
> 
> bjorn@...ardo:/usr/local/src/build-tmp/linux$ git bisect log
> # bad: [29594404d7fe73cd80eaa4ee8c43dcc53970c60e] Linux 3.7
> # good: [8f0d8163b50e01f398b14bcd4dc039ac5ab18d64] Linux 3.7-rc3
> git bisect start 'v3.7' 'v3.7-rc3'
> # good: [29282fde80d44e587f8c152b10049a56e61659f0] KVM: x86: Fix invalid
> secondary exec controls in vmx_cpuid_update() git bisect good
> 29282fde80d44e587f8c152b10049a56e61659f0
> # good: [2654ad44b5f7a5f1b12d722a37d9b9df69d57899] Merge branch
> 'x86-urgent-for-linus' of
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip git bisect good
> 2654ad44b5f7a5f1b12d722a37d9b9df69d57899
> # good: [086486e46e4206cfa1140fb9682ad67c8a4502fb] Merge branch 'for-linus'
> of git://git.samba.org/sfrench/cifs-2.6 git bisect good
> 086486e46e4206cfa1140fb9682ad67c8a4502fb
> # good: [25a3bc6bd1ca03ab504b8c55c98f8d0135644d53] [parisc] open(2) compat
> bug git bisect good 25a3bc6bd1ca03ab504b8c55c98f8d0135644d53
> # bad: [cfd1f032f98e5ab3a04f23a0adbd53ff8744827d] Merge branch
> 'core-urgent-for-linus' of
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip git bisect bad
> cfd1f032f98e5ab3a04f23a0adbd53ff8744827d
> # good: [b69f0859dc8e633c5d8c06845811588fe17e68b3] Linux 3.7-rc8
> git bisect good b69f0859dc8e633c5d8c06845811588fe17e68b3
> # good: [ca50496eb487b639de1f502e77a48dde84152fb9] Merge branch
> 'for-3.7-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq git
> bisect good ca50496eb487b639de1f502e77a48dde84152fb9
> # good: [70dcc535bdf30ffaef58b867fbde45c0287f34c6] Merge tag
> 'upstream-3.7-rc9' of git://git.infradead.org/linux-ubi git bisect good
> 70dcc535bdf30ffaef58b867fbde45c0287f34c6
> # good: [df2fc246c8ee8b6067af1fa55d3bc23107457f61] Merge branch 'fixes' of
> git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux git bisect good
> df2fc246c8ee8b6067af1fa55d3bc23107457f61
> # bad: [8d4516904b39507458bee8115793528e12b1d8dd] watchdog: Fix CPU hotplug
> regression git bisect bad 8d4516904b39507458bee8115793528e12b1d8dd
> 
> 
> and I can confirm that reverting 8d451690 does fix the problem.  After
> having found this, it became clearer to me why the freeze was related to
> plugging AC power: I use laptop-mode-tools in its default Debian
> configuration, which will disable the nmi_watchdog on battery power and
> enable it on AC power.
> 
> So the simple test case which will hang my (and presumably also your) PC
> on plain v3.7 is:
> 
>  echo 0 > /proc/sys/kernel/nmi_watchdog
>  echo 1 > /proc/sys/kernel/nmi_watchdog
> 
> without any cmdline nmi_watchdog parameters, i.e. enabled.
> 
> I'll followup with a proposed revert patch, but I guess you will want to
> come up with something which fixes the original problem as well.  But
> given the serious effect of the bug, causing a 100% reproducable freeze
> on a standard distro laptop setup, I hope that the revert will go into
> v3.7.1 unless a real fix can be prepared in time.
> 
> 
> Thanks,
> Bjørn

Confirm similar behaviour (I didn't do bisection): kernel sometimes opps when 
plug in AC adapter.

Regards

-- 
Maciej Rutecki
http://www.mrutecki.pl
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