Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934397Ab3JPNhQ (ORCPT ); Wed, 16 Oct 2013 09:37:16 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.226]:12604 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1760554Ab3JPNhO (ORCPT ); Wed, 16 Oct 2013 09:37:14 -0400 Date: Wed, 16 Oct 2013 09:37:12 -0400 From: Steven Rostedt To: Frederic Weisbecker Cc: LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , "paulmck@linux.vnet.ibm.com" , Peter Zijlstra , "x86@kernel.org" , "Wang, Xiaoming" , "Li, Zhuangzhi" , "Liu, Chuansheng" Subject: Re: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc_fault Message-ID: <20131016093712.0d258870@gandalf.local.home> In-Reply-To: <20131016132813.GB14938@localhost.localdomain> References: <20131015163906.342d8ffa@gandalf.local.home> <20131016114036.GB12773@localhost.localdomain> <20131016084518.44eaf61a@gandalf.local.home> <20131016130856.GE12773@localhost.localdomain> <20131016091437.146cb9d4@gandalf.local.home> <20131016132813.GB14938@localhost.localdomain> X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.20; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.130:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1925 Lines: 44 On Wed, 16 Oct 2013 15:28:15 +0200 Frederic Weisbecker wrote: > On Wed, Oct 16, 2013 at 09:14:37AM -0400, Steven Rostedt wrote: > > On Wed, 16 Oct 2013 15:08:57 +0200 > > Frederic Weisbecker wrote: > > > > > > > Faults can call rcu_user_exit() / rcu_user_enter(). This is not supposed to happen > > > between rcu_nmi_enter() and rcu_nmi_exit(). rdtp->dynticks would be incremented in the > > > wrong way. > > > > > > Ah but we have an in_interrupt() check in context_tracking_user_enter() that protects > > > us against that. > > > > I will say that we should probably warn if it's any fault other than a > > vmalloc fault. A vmalloc fault should only happen in kernel space, and > > should not be happening from user code. > > The NMI can interrupt userspace. When the fault happens, it sees that context tracking > state is set to userspace (NMIs and interrupts in general don't exit that state, hence > the in_interrupt() check that returns when user_exit/enter is called) so it calls user_enter(). > But anyway we should be protected against that. IIRC, NMI itself is safe to use rcu_read_lock(), at least I remember Paul making sure that stuff was lockless and NMI safe. > > The WARN_ON() that I removed is from vmalloc fault. I don't see an > > issue with NMIs faulting via vmalloc. For any other page fault, sure, I > > would be concerned about it. But what's wrong with an NMI running > > module code? > > I won't argue further as none of us is going to change his opinion on this :) Sure sure, yet another argument continues with two sides stubbornly refusing to negotiate about a looming future (de)fault! -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/