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Date: Thu, 5 Jan 2017 08:49:42 -0600
From: Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: x86: warning in unwind_get_return_address
Message-ID: <20170105144942.whqucdwmeqybng3s@treble>
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To: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>, syzkaller <syzkaller@googlegroups.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, kasan-dev <kasan-dev@googlegroups.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, "x86@kernel.org" <x86@kernel.org>, Kostya Serebryany <kcc@google.com>

On Tue, Dec 27, 2016 at 05:38:59PM +0100, Dmitry Vyukov wrote:
> On Thu, Dec 22, 2016 at 6:17 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > On Wed, Dec 21, 2016 at 01:46:36PM +0100, Andrey Konovalov wrote:
> >> On Wed, Dec 21, 2016 at 12:36 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >> >
> >> > Thanks.  Looking at the stack trace, my guess is that an interrupt hit
> >> > while running in generated BPF code, and the unwinder got confused
> >> > because regs->ip points to the generated code.  I may need to disable
> >> > that warning until we figure out a better solution.
> >> >
> >> > Can you share your .config file?
> >>
> >> Sure, attached.
> >
> > Ok, I was able to recreate with your config.  The culprit was generated
> > code, as I suspected, though it wasn't BPF, it was a kprobe (created by
> > dccpprobe_init()).
> >
> > I'll make a patch to disable the warning.
> 
> Hi,
> 
> I am also seeing the following warnings:
> 
> [  281.889259] WARNING: kernel stack regs at ffff8801c29a7ea8 in
> syz-executor8:1302 has bad 'bp' value ffff8801c29a7f28
> [  833.994878] WARNING: kernel stack regs at ffff8801c4e77ea8 in
> syz-executor1:13094 has bad 'bp' value ffff8801c4e77f28
> 
> Can it also be caused by bpf/kprobe?

This is a different warning.  I suspect it's due to unwinding the stack
of another CPU while it's running, which is still possible in a few
places.  I'm going to have to disable all these warnings for now.

-- 
Josh

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