linux-kernel - Re:Please review arch/x86/kernel/pvclock.c to fix Docker/Mono crashes in new Kernels

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Message-Id: <4696251463489989@web4g.yandex.ru>
Date:	Tue, 17 May 2016 15:59:49 +0300
From:	okhalzov@...m.vestbery.com
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Taloth Saldono <talothsaldono@...il.com>
Subject: Re:Please review arch/x86/kernel/pvclock.c to fix Docker/Mono crashes in new Kernels

Hi Paolo,

the crashes occure on bare-metal (3.13.0-49-generic) and Docker is inside of VMWare vCenter (4.2.0-35-generic).
On 3.19.0-25-generic with some highload (200 client requests simultaneously) in Docker inside of VMWare vCenter it doesn't crash.

--
Олег Хальзов
SDE
Vestbery

17.05.2016, 14:06, "Paolo Bonzini" <pbonzini@...hat.com>:

> On 16/05/2016 20:56, Linus Torvalds wrote:
>
>> On Mon, May 16, 2016 at 11:37 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>>> All of those fixes were intended to fix incorrect times being
>>> reported, not segfaults. Weird.
>>
>> I'm assuming it's "time going backwards". I can easily see that
>> causing segfaults.
>
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1450584 says the
> crashes occurs "more frequently on a vbox vm with multiple CPUs
> configured". If vbox tells the VM to use the vdso when it shouldn't
> (because the TSC is not stable on the host), bad things could happen.
>
> However, based on the Xamarin bug comments and
> http://lists.ximian.com/pipermail/mono-devel-list/2015-August/043181.html,
> it looks like vbox after all doesn't use pvclock and the trigger seems
> to be https://github.com/torvalds/linux/commit/c70e1b475f37:
>
> With __always_inline on vread_pvclock, mono crashed. With noinline on
> vread_pvclock, mono doesn't crash. Weirdest part is that the pvclock
> isn't even used during my tests.
>
> Oleg, what is your environment exactly? You mentioned Docker, but are
> you also virtualizing and if so what is your hypervisor?
>
> Taloth, do you know if it can it be reproduced under Xen or KVM or
> bare-metal? I'd trust them more than VirtualBox regarding timekeeping.
> I saw Amazon Linux mentioned in the mono mailing list archives which
> would point to Xen. Xen doesn't use the pvclock vdso code either, though.
>
> Thanks,
>
> Paolo