From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765483AbYFFQP4 (ORCPT ); Fri, 6 Jun 2008 12:15:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1765228AbYFFQOJ (ORCPT ); Fri, 6 Jun 2008 12:14:09 -0400 Received: from terminus.zytor.com ([198.137.202.10]:50603 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1765213AbYFFQOI (ORCPT ); Fri, 6 Jun 2008 12:14:08 -0400 Message-ID: <484961FC.5030800@zytor.com> Date: Fri, 06 Jun 2008 09:12:44 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, minyard@acm.org, dvhltc@us.ibm.com, niv@us.ibm.com Subject: Re: Recoverable MCA interrupts from NMI handlers? IPMI and RCU? References: <20080606152134.GA13641@linux.vnet.ibm.com> In-Reply-To: <20080606152134.GA13641@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul E. McKenney wrote: > Hello! > > A couple of questions about the x86 architecture... > > 1. Can recoverable machine-check exceptions occur from within > NMI handlers? If so, there is a bug in preemptable RCU's > CONFIG_NO_HZ handling that could be fixed by a patch something > like the one shown below (untested, probably does not even > compile). > In theory, recoverable #MC's can occur anywhere. It's an exception. > 2. Does the IPMI subsystem make use of RCU read-side primitives > from within SMI handlers? If so, we need the SMI handlers to > invoke rcu_irq_enter() upon entry and rcu_irq_exit() upon exit > when they are invoked from dynticks idle state. Or something > similar, depending on restrictions on code within SMI handlers. Not sure about that one. I clearly need to look carefully into this... SMI is quite "special" in that it sets up an entirely new environment; the concept of executing kernel code at SMI level makes me want to run away and hide. -hpa