Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759249AbZCCAcW (ORCPT ); Mon, 2 Mar 2009 19:32:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753409AbZCCAcO (ORCPT ); Mon, 2 Mar 2009 19:32:14 -0500 Received: from mx2.redhat.com ([66.187.237.31]:57523 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750882AbZCCAcN (ORCPT ); Mon, 2 Mar 2009 19:32:13 -0500 Message-ID: <49AC7A5F.7080009@redhat.com> Date: Mon, 02 Mar 2009 19:31:27 -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: <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> <49AC7453.8020307@redhat.com> <20090303002214.GA4147@elte.hu> In-Reply-To: <20090303002214.GA4147@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: 2503 Lines: 69 Ingo Molnar wrote: > * Masami Hiramatsu wrote: > >> >> 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. :-) > > yeah, but still the API is somewhat unsafe. Yeah, kprobe_mutex protects text_poke from other kprobes, but not from other text_poke() users... > In any case, you also answered your own question: > >>>> 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? > > kprobe_mutex does that. Anyway, text_edit_lock ensures that. By the way, I think set_fixmap/clear_fixmap seems simpler than kmap_atomic() variant. Would you think improving kmap_atomic_prot() is better? > > 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/ -- 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/