From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754332AbaAaVns (ORCPT ); Fri, 31 Jan 2014 16:43:48 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:51773 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754033AbaAaVnr (ORCPT ); Fri, 31 Jan 2014 16:43:47 -0500 Date: Fri, 31 Jan 2014 13:43:45 -0800 From: Andrew Morton To: Michel Lespinasse Cc: =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker , Salman Qazi , LKML Subject: Re: Reverting warning for vmalloc and kmemcheck faults in NMI Message-Id: <20140131134345.0d63bce0fc19d5fe86541e13@linux-foundation.org> In-Reply-To: References: X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 30 Jan 2014 19:06:58 -0800 Michel Lespinasse wrote: > Hi, > > Way back in 2010, Frederic added commit > ebc8827f75954fe315492883eee5cb3f355d547d to warn us about cases where > faults were incorrectly firing during NMI handling on x86, as the IRET > from such faults would possibly trigger nested NMIs. > > Later (2012), Salman added commit > 28696f434fef0efa97534b59986ad33b9c4df7f8 to enable nested NMI > handling. See http://lwn.net/Articles/484932/ > > So, I believe such faults nesting under NMI are not an issue anymore, > and we could revert ebc8827f75954fe315492883eee5cb3f355d547d ? Seems logical. > Background: I'm asking this because at Google we like to dump memory > regions pointed by registers in our arch_trigger_all_cpu_backtrace > handler, and this occasionally causes the vmalloc_fault in_nmi() > warning to fire. > It seems odd that x86 arch_trigger_all_cpu_backtrace() uses NMI - why didn't it use the regular old IPI? If a CPU is stuck with interrupts disable, the NMI watchdog will provide the diagnostic?