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Date: Thu, 19 Mar 2015 15:55:26 +0100
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From: Takashi Iwai <tiwai@suse.de>
To: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
        Andy Lutomirski <luto@amacapital.net>, Jiri Kosina <jkosina@suse.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Stefan Seyfried <stefan.seyfried@googlemail.com>,
        X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>
Subject: Re: PANIC: double fault, error_code: 0x0 in 4.0.0-rc3-2, kvm related?
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At Thu, 19 Mar 2015 14:47:12 +0100,
Takashi Iwai wrote:
> 
> At Thu, 19 Mar 2015 13:48:56 +0100,
> Denys Vlasenko wrote:
> > 
> > Having no more ideas at the moment, here is a tarball of 13 patches
> > of commits touching entry_64.S up to 4.0.0-rc1.
> > 
> > x0001.patch is the latest, x0015.patch is the oldest.
> > 
> > Patches 0003 and 0008 are not there since 0003 is empty merge patch
> > and 0008 does some PCI fixup.
> > 
> > If this breakage is recent, it ought to be one of these.
> > Most of them do some non-trivial surgery.
> > 
> > Even though I did not spot anything suspicious in them,
> > entry.S is notorious for subtle breakage.
> > 
> > Try reverting them in sequence starting from x0001.patch
> > and see reverting which one makes crash disappear.
> 
> OK, I'm going to check these git series.

Reverting the commit
96b6352c12711d5c0bb7157f49c92580248e8146
    x86_64, entry: Remove the syscall exit audit and schedule optimizations

seems enough.  After reverting this one, the machine runs stable with
the kvm stress test.

(I'll keep test running for a while; at the previous bisection, I hit
 the bug right after posting the mail ;)

BTW, I also tried to reproduce this on another machine (a Haswell
laptop), but I failed, even with the very same kernel.  So the bug
really seems depending on CPU.


Takashi