From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933092AbbDWJNf (ORCPT ); Thu, 23 Apr 2015 05:13:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58873 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932367AbbDWJNb (ORCPT ); Thu, 23 Apr 2015 05:13:31 -0400 Message-ID: <5538B7B3.2020009@redhat.com> Date: Thu, 23 Apr 2015 11:13:23 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: Marcelo Tosatti , Andy Lutomirski CC: Peter Zijlstra , Linus Torvalds , "linux-kernel@vger.kernel.org" , Gleb Natapov , kvm list , Ralf Baechle , Andrew Lutomirski Subject: Re: [GIT PULL] First batch of KVM changes for 4.1 References: <5530E28F.2030401@redhat.com> <20150417105506.GF5029@twins.programming.kicks-ass.net> <553100C1.5000408@redhat.com> <20150417131037.GG23123@twins.programming.kicks-ass.net> <55310CF2.6070107@redhat.com> <20150417190146.GA24395@amt.cnet> <55316598.908@redhat.com> <20150417201841.GA31302@amt.cnet> <55353058.2000008@redhat.com> <20150422212148.GA17494@amt.cnet> In-Reply-To: <20150422212148.GA17494@amt.cnet> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/04/2015 23:21, Marcelo Tosatti wrote: > On Mon, Apr 20, 2015 at 01:27:58PM -0700, Andy Lutomirski wrote: >> On Mon, Apr 20, 2015 at 9:59 AM, Paolo Bonzini wrote: >>> >>> >>> On 17/04/2015 22:18, Marcelo Tosatti wrote: >>>> The bug which this is fixing is very rare, have no memory of a report. >>>> >>>> In fact, its even difficult to create a synthetic reproducer. >>> >>> But then why was the task migration notifier even in Jeremy's original >>> code for Xen? Was it supposed to work even on non-synchronized TSC? >>> >>> If that's the case, then it could be reverted indeed; but then why did >>> you commit this patch to 4.1? Did you think of something that would >>> cause the seqcount-like protocol to fail, and that turned out not to be >>> the case later? I was only following the mailing list sparsely in March. >> >> I don't think anyone ever tried that hard to test this stuff. There >> was an infinte loop that Firefox was triggering as a KVM guest >> somewhat reliably until a couple months ago in the same vdso code. :( > > https://bugzilla.redhat.com/show_bug.cgi?id=1174664 That was the missing volatile in an asm. Older compilers didn't catch it. :( Paolo