From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raghavendra K T Subject: Re: [PATCH RFC V10 15/18] kvm : Paravirtual ticketlocks support for linux guests running on KVM hypervisor Date: Wed, 17 Jul 2013 00:19:42 +0530 Message-ID: <51E595C6.9020708@linux.vnet.ibm.com> References: <20130624124014.27508.8906.sendpatchset@codeblue.in.ibm.com> <20130624124342.27508.44656.sendpatchset@codeblue.in.ibm.com> <20130714131241.GA11772@redhat.com> <51E3C5CE.7000009@linux.vnet.ibm.com> <20130715103648.GN11772@redhat.com> <51E4C011.4060803@linux.vnet.ibm.com> <20130716060215.GE11772@redhat.com> <20130716154852.GN23818@dyad.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130716154852.GN23818@dyad.programming.kicks-ass.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Peter Zijlstra Cc: jeremy@goop.org, gregkh@suse.de, kvm@vger.kernel.org, linux-doc@vger.kernel.org, drjones@redhat.com, virtualization@lists.linux-foundation.org, andi@firstfloor.org, hpa@zytor.com, stefano.stabellini@eu.citrix.com, xen-devel@lists.xensource.com, x86@kernel.org, mingo@redhat.com, habanero@linux.vnet.ibm.com, riel@redhat.com, konrad.wilk@oracle.com, ouyang@cs.pitt.edu, avi.kivity@gmail.com, tglx@linutronix.de, chegu_vinod@hp.com, linux-kernel@vger.kernel.org, srivatsa.vaddagiri@gmail.com, attilio.rao@citrix.com, pbonzini@redhat.com, torvalds@linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On 07/16/2013 09:18 PM, Peter Zijlstra wrote: > On Tue, Jul 16, 2013 at 09:02:15AM +0300, Gleb Natapov wrote: >> BTW can NMI handler take spinlocks? > > No -- that is, yes you can using trylock, but you still shouldn't. Thanks Peter for the clarification. I had started checking few of nmi handlers code to confirm. Did saw a raw spinlock in drivers/acpi/apei/ghes.c, but then stopped. > >> If it can what happens if NMI is >> delivered in a section protected by local_irq_save()/local_irq_restore()? > > You deadlock. > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933662Ab3GPSqZ (ORCPT ); Tue, 16 Jul 2013 14:46:25 -0400 Received: from e23smtp07.au.ibm.com ([202.81.31.140]:40678 "EHLO e23smtp07.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933306Ab3GPSqX (ORCPT ); Tue, 16 Jul 2013 14:46:23 -0400 Message-ID: <51E595C6.9020708@linux.vnet.ibm.com> Date: Wed, 17 Jul 2013 00:19:42 +0530 From: Raghavendra K T Organization: IBM User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121029 Thunderbird/16.0.2 MIME-Version: 1.0 To: Peter Zijlstra CC: Gleb Natapov , mingo@redhat.com, jeremy@goop.org, x86@kernel.org, konrad.wilk@oracle.com, hpa@zytor.com, pbonzini@redhat.com, linux-doc@vger.kernel.org, habanero@linux.vnet.ibm.com, xen-devel@lists.xensource.com, mtosatti@redhat.com, stefano.stabellini@eu.citrix.com, andi@firstfloor.org, attilio.rao@citrix.com, ouyang@cs.pitt.edu, gregkh@suse.de, agraf@suse.de, chegu_vinod@hp.com, torvalds@linux-foundation.org, avi.kivity@gmail.com, tglx@linutronix.de, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, riel@redhat.com, drjones@redhat.com, virtualization@lists.linux-foundation.org, srivatsa.vaddagiri@gmail.com Subject: Re: [PATCH RFC V10 15/18] kvm : Paravirtual ticketlocks support for linux guests running on KVM hypervisor References: <20130624124014.27508.8906.sendpatchset@codeblue.in.ibm.com> <20130624124342.27508.44656.sendpatchset@codeblue.in.ibm.com> <20130714131241.GA11772@redhat.com> <51E3C5CE.7000009@linux.vnet.ibm.com> <20130715103648.GN11772@redhat.com> <51E4C011.4060803@linux.vnet.ibm.com> <20130716060215.GE11772@redhat.com> <20130716154852.GN23818@dyad.programming.kicks-ass.net> In-Reply-To: <20130716154852.GN23818@dyad.programming.kicks-ass.net> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13071618-0260-0000-0000-000003518AB5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/16/2013 09:18 PM, Peter Zijlstra wrote: > On Tue, Jul 16, 2013 at 09:02:15AM +0300, Gleb Natapov wrote: >> BTW can NMI handler take spinlocks? > > No -- that is, yes you can using trylock, but you still shouldn't. Thanks Peter for the clarification. I had started checking few of nmi handlers code to confirm. Did saw a raw spinlock in drivers/acpi/apei/ghes.c, but then stopped. > >> If it can what happens if NMI is >> delivered in a section protected by local_irq_save()/local_irq_restore()? > > You deadlock. >