linux-kernel - Re: BUG: unable to handle kernel paging request in __switch

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Message-ID: <alpine.DEB.2.20.1712151047400.1702@nanos>
Date:   Fri, 15 Dec 2017 10:49:43 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dmitry Vyukov <dvyukov@...gle.com>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        syzbot 
        <bot+1f445b1009b8eeededa30fe62ccf685f2ec9d155@...kaller.appspotmail.com>,
        Borislav Petkov <bp@...e.de>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Peter Anvin <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kyle Huey <me@...ehuey.com>, Ingo Molnar <mingo@...hat.com>,
        syzkaller-bugs@...glegroups.com,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: BUG: unable to handle kernel paging request in __switch_to

On Fri, 15 Dec 2017, Dmitry Vyukov wrote:
> I've built this exact kernel and here is __switch_to disasm:
> https://gist.githubusercontent.com/dvyukov/8137559f7da08fbe32f9018972a4498c/raw/0ef2abf723b117f0d0f0306fd50e216d50c5cecb/gistfile1.txt
> 
> __switch_to+0x95b seems to point to (?):
> 
> ffffffff81252f6b: 0f 1f 44 00 00        nopl   0x0(%rax,%rax,1)
> 
> which is branch target alignment nop.

Which is a place holder for a trace point as Linus pointed out and the
'faulting' instruction which is int3 shows that there is a tracepoint
install/remove in progress. Are your test cases fiddling with tracepoints?

Thanks,

	tglx