linux-kernel - Re: general protection fault in finish_task

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Message-ID: <20180822090823.GT24124@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Aug 2018 11:08:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     syzbot <syzbot+1f56df64bfb3c29dde6f@...kaller.appspotmail.com>
Cc:     dvhart@...radead.org, hpa@...or.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        pbonzini@...hat.com, rkrcmar@...hat.com,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de, x86@...nel.org
Subject: Re: general protection fault in finish_task_switch (2)

On Tue, Aug 21, 2018 at 02:28:02PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    778a33959a8a Merge tag 'please-pull-noboot' of git://git.k..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a5385a400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=214e4990bd49329f
> dashboard link: https://syzkaller.appspot.com/bug?extid=1f56df64bfb3c29dde6f
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> userspace arch: i386
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=13ffa561400000

FWIW the lack of whitespace between "repro:" and the URL makes it hard
to copy paste.

> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10023961400000


> RIP: 0010:__fire_sched_in_preempt_notifiers kernel/sched/core.c:2481

That repro thing does something dodgy with KVM, which then corrupts the
premption notifier thing. I'm sufficiently KVM clueless to not really
know where to start looking though..