Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753855AbYJDOoq (ORCPT ); Sat, 4 Oct 2008 10:44:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753025AbYJDOoi (ORCPT ); Sat, 4 Oct 2008 10:44:38 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:41217 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752850AbYJDOoh (ORCPT ); Sat, 4 Oct 2008 10:44:37 -0400 Date: Sat, 4 Oct 2008 16:44:23 +0200 From: Ingo Molnar To: Steven Rostedt Cc: LKML , Thomas Gleixner , Peter Zijlstra , Andrew Morton , Linus Torvalds , Mathieu Desnoyers , Arjan van de Ven Subject: Re: [PATCH 0/3] ring-buffer: less locking and only disable preemption Message-ID: <20081004144423.GA14918@elte.hu> References: <20081004060057.660306328@goodmis.org> <20081004084002.GE27624@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1386 Lines: 30 * Steven Rostedt wrote: > The dynamic function tracer is another issue. The problem with NMIs > has nothing to do with locking, or corrupting the buffers. It has to > do with the dynamic code modification. Whenever we modify code, we > must guarantee that it will not be executed on another CPU. > > Kstop_machine serves this purpose rather well. We can modify code > without worrying it will be executed on another CPU, except for NMIs. > The problem now comes where an NMI can come in and execute the code > being modified. That's why I put in all the notrace, lines. But it > gets difficult because of nmi_notifier can call all over the kernel. > Perhaps, we can simply disable the nmi-notifier when we are doing the > kstop_machine call? that would definitely be one way to reduce the cross section, but not enough i'm afraid. For example in the nmi_watchdog=2 case we call into various lapic functions and paravirt lapic handlers which makes it all spread to 3-4 paravirtualization flavors ... sched_clock()'s notrace aspects were pretty manageable, but this in its current form is not. Ingo -- 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/