Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758771AbZCCAGz (ORCPT ); Mon, 2 Mar 2009 19:06:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751491AbZCCAGq (ORCPT ); Mon, 2 Mar 2009 19:06:46 -0500 Received: from mx2.redhat.com ([66.187.237.31]:35974 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751447AbZCCAGp (ORCPT ); Mon, 2 Mar 2009 19:06:45 -0500 Message-ID: <49AC7453.8020307@redhat.com> Date: Mon, 02 Mar 2009 19:05:39 -0500 From: Masami Hiramatsu User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Ingo Molnar CC: Mathieu Desnoyers , Andrew Morton , Nick Piggin , Steven Rostedt , Andi Kleen , linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" , Steven Rostedt Subject: Re: [RFC][PATCH] x86: make text_poke() atomic References: <49A83237.40604@redhat.com> <20090227185316.GA19811@Krystal> <49A853CD.3020607@redhat.com> <49AC10E9.1090102@redhat.com> <20090302171914.GB21735@Krystal> <49AC5A87.7000604@redhat.com> <20090302222254.GA31962@elte.hu> <49AC63FA.70801@redhat.com> <20090302230915.GA11626@elte.hu> <49AC6DEA.2050304@redhat.com> <20090302234910.GA17956@elte.hu> In-Reply-To: <20090302234910.GA17956@elte.hu> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1954 Lines: 59 Ingo Molnar wrote: > * Masami Hiramatsu wrote: > >> Ingo Molnar wrote: >>>>> So perhaps another approach to (re-)consider would be to go back >>>>> to atomic fixmaps here. It spends 3 slots but that's no big >>>>> deal. >>>> Oh, it's a good idea! fixmaps must make it simpler. >>>> >>>>> In exchange it will be conceptually simpler, and will also scale >>>>> much better than a global spinlock. What do you think? >>>> I think even if I use fixmaps, we have to use a spinlock to protect >>>> the fixmap area from other threads... >>> that's why i suggested to use an atomic-kmap, not a fixmap. >> Even if the mapping is atomic, text_poke() has to protect pte >> from other text_poke()s while changing code. >> AFAIK, atomic-kmap itself doesn't ensure that, does it? > > Well, but text_poke() is not a serializing API to begin with. > It's normally used in code patching sequences when we 'know' > that there cannot be similar parallel activities. The kprobes > usage of text_poke() looks unsafe - and that needs to be fixed. Oh, kprobes already prohibited parallel arming/disarming by using kprobe_mutex. :-) > So indeed a new global lock is needed there. > > It's fixable and we'll fixit, but text_poke() is really more > complex than i'd like it to be. > > stop_machine_run() is essentially instantaneous in practice and > obviously serializing so it warrants a second look at least. > Have you tried to use it in kprobes? No, but it seems that cost high for incremental use(registration) of kprobes... Thank you, > > Ingo -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division e-mail: mhiramat@redhat.com -- 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/