From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andre Przywara Subject: Re: 2.6.35-rc1 regression with pvclock and smp guests Date: Mon, 26 Jul 2010 10:47:07 +0200 Message-ID: <4C4D4B8B.80006@amd.com> References: <4C483F67.1010007@amd.com> <4C4BF96B.7010005@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: "glommer@redhat.com" , Zachary Amsden , KVM list To: Avi Kivity Return-path: Received: from tx2ehsobe004.messaging.microsoft.com ([65.55.88.14]:7313 "EHLO TX2EHSOBE007.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752715Ab0GZIsV (ORCPT ); Mon, 26 Jul 2010 04:48:21 -0400 In-Reply-To: <4C4BF96B.7010005@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > On 07/22/2010 03:53 PM, Andre Przywara wrote: >> Hi, >> >> I found a regression with pvclock and SMP KVM _guests_. >> PVCLOCK enabled guest kernels boot with qemu-kvm.git and with smp=1, >> but with smp=2 halt at: >> >> Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled >> (last line shown) >> >> I bisected this down to: >> commit 489fb490dbf8dab0249ad82b56688ae3842a79e8 >> Author: Glauber Costa >> Date: Tue May 11 12:17:40 2010 -0400 >> >> x86, paravirt: Add a global synchronization point for pvclock >> >> One commit before works, smp=1 always works, disabling PVCLOCK works. >> Using qemu-kvm-0.12.4 works, too. >> Having PVCLOCK enabled and with smp=2 the kernel halts without any >> further message. >> This is still the case with the lastest tip. >> Even pinning both VCPU threads to the same host core show the bug. >> The bug triggers on all hosts I tested, an single socket quadcore >> Athlon, a dual socket dualcore K8-Opteron and a quad socket 12core >> Opteron. >> >> Please note that this is the guest kernel, the host kernel does not >> matter. >> >> I have no idea (and don't feel like ;-) debugging this, so I hope >> someone will find and fix the bug. > > > Does this go away with CONFIG_DEBUG_RODATA=n? If so, it's a known bug > in the atomic_*() clobber lists. > Unfortunately the bug persists even with CONFIG_DEBUG_RODATA disabled. The debug options I had enabled now are: CONFIG_DEBUG_DEVRES=y CONFIG_DEBUG_FS=y CONFIG_DEBUG_KERNEL=y CONFIG_DEBUG_BUGVERBOSE=y CONFIG_DEBUG_MEMORY_INIT=y CONFIG_DEBUG_STACKOVERFLOW=y CONFIG_DEBUG_BOOT_PARAMS=y I even disabled all kernel debug options, that does not help, too. Regards, Andre. -- Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany Tel: +49 351 448-3567-12