From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zachary Amsden Subject: Re: [PATCH 1/2] KVM: take kvm_lock for hardware_disable() during cpu hotplug Date: Wed, 17 Nov 2010 19:45:34 -1000 Message-ID: <4CE4BD7E.3040406@redhat.com> References: <20101116173244.c5d2e812.yoshikawa.takuya@oss.ntt.co.jp> <20101116173502.96ff13f3.yoshikawa.takuya@oss.ntt.co.jp> <4CE4889A.7010808@redhat.com> <4CE489A6.4010100@oss.ntt.co.jp> <4CE4908F.3050209@redhat.com> <4CE49264.8020103@oss.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: avi@redhat.com, mtosatti@redhat.com, kvm@vger.kernel.org, takuya.yoshikawa@gmail.com To: Takuya Yoshikawa Return-path: Received: from mx1.redhat.com ([209.132.183.28]:16548 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751254Ab0KRFpk (ORCPT ); Thu, 18 Nov 2010 00:45:40 -0500 In-Reply-To: <4CE49264.8020103@oss.ntt.co.jp> Sender: kvm-owner@vger.kernel.org List-ID: On 11/17/2010 04:41 PM, Takuya Yoshikawa wrote: > (2010/11/18 11:33), Zachary Amsden wrote: >> On 11/17/2010 04:04 PM, Takuya Yoshikawa wrote: >>> (2010/11/18 10:59), Zachary Amsden wrote: >>>> On 11/15/2010 10:35 PM, Takuya Yoshikawa wrote: >>>>> In kvm_cpu_hotplug(), only CPU_STARTING case is protected by >>>>> kvm_lock. >>>>> This patch adds missing protection for CPU_DYING case. >>>>> >>>>> Signed-off-by: Takuya Yoshikawa >>>>> --- >>>>> virt/kvm/kvm_main.c | 2 ++ >>>>> 1 files changed, 2 insertions(+), 0 deletions(-) >>>>> >>>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c >>>>> index 339dd43..0fdd911 100644 >>>>> --- a/virt/kvm/kvm_main.c >>>>> +++ b/virt/kvm/kvm_main.c >>>>> @@ -2148,7 +2148,9 @@ static int kvm_cpu_hotplug(struct >>>>> notifier_block *notifier, unsigned long val, >>>>> case CPU_DYING: >>>>> printk(KERN_INFO "kvm: disabling virtualization on CPU%d\n", >>>>> cpu); >>>>> + spin_lock(&kvm_lock); >>>>> hardware_disable(NULL); >>>>> + spin_unlock(&kvm_lock); >>>>> break; >>>>> case CPU_STARTING: >>>>> printk(KERN_INFO "kvm: enabling virtualization on CPU%d\n", >>>> >>>> I believe this is correct. >>> >>> You mean lock is not necessary? >> >> No, I believe your patch is correct and the lock should be there. Did >> you test with spinlock debugging just to be sure? >> > > Sorry but no. > > I have no experience with cpu hotplug. > > So I thought it would take too much time to do real test by myself and > reported like this this time. > > Any easy way to test? Yes, quite easy. Some systems may not let cpu0 go offline, but you can manually disable and re-enable the other processors: [root@mysore ~]# echo "0" > /sys/devices/system/cpu/cpu1/online [root@mysore ~]# echo "1" > /sys/devices/system/cpu/cpu1/online Cheers, Zach