From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755985AbYDZL7E (ORCPT ); Sat, 26 Apr 2008 07:59:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751555AbYDZL6v (ORCPT ); Sat, 26 Apr 2008 07:58:51 -0400 Received: from mx1.redhat.com ([66.187.233.31]:55192 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751445AbYDZL6u (ORCPT ); Sat, 26 Apr 2008 07:58:50 -0400 Date: Sat, 26 Apr 2008 08:56:34 -0300 From: Arnaldo Carvalho de Melo To: Jeremy Fitzhardinge Cc: Masami Hiramatsu , Mathieu Desnoyers , Linus Torvalds , "H. Peter Anvin" , Andi Kleen , Ingo Molnar , Jiri Slaby , David Miller , zdenek.kabelac@gmail.com, rjw@sisk.pl, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, linux-ext4@vger.kernel.org, herbert@gondor.apana.org.au, penberg@cs.helsinki.fi, clameter@sgi.com, linux-kernel@vger.kernel.org, pageexec@freemail.hu, "Frank Ch. Eigler" , systemtap@sources.redhat.com Subject: Re: [PATCH 1/1] x86: fix text_poke Message-ID: <20080426115634.GH16635@ghostprotocols.net> Mail-Followup-To: Arnaldo Carvalho de Melo , Jeremy Fitzhardinge , Masami Hiramatsu , Mathieu Desnoyers , Linus Torvalds , "H. Peter Anvin" , Andi Kleen , Ingo Molnar , Jiri Slaby , David Miller , zdenek.kabelac@gmail.com, rjw@sisk.pl, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, linux-ext4@vger.kernel.org, herbert@gondor.apana.org.au, penberg@cs.helsinki.fi, clameter@sgi.com, linux-kernel@vger.kernel.org, pageexec@freemail.hu, "Frank Ch. Eigler" , systemtap@sources.redhat.com References: <48123C9B.9020306@zytor.com> <20080425203717.GB25950@Krystal> <481241DC.3070601@zytor.com> <20080425211205.GC25950@Krystal> <20080425230028.GC31226@Krystal> <481265B7.9040505@goop.org> <48126A80.4000203@redhat.com> <4812CA02.8040705@goop.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4812CA02.8040705@goop.org> X-Url: http://oops.ghostprotocols.net:81/blog User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Fri, Apr 25, 2008 at 11:21:54PM -0700, Jeremy Fitzhardinge escreveu: > Masami Hiramatsu wrote: >> Jeremy Fitzhardinge wrote: >> >>> Mathieu Desnoyers wrote: >>> >>>> This idea has been considered a few years ago at OLS in the tracing BOF >>>> if I remember well. The results were this : First, there is no way to >>>> guarantee that no code path, nor any return address from any function, >>>> interrupt, sleeping thread, will return to the "old" version of the >>>> function. Nor is it possible to determine when a quiescent state is >>>> reached. Therefore, we couldn't see how we can do the teardown. >>>> >>> Does that matter? The new function is semantically identical to the old >>> one, and the old code will remain in place. If there's still users in >>> the old function it may take a while for them to get flushed out (and >>> won't be traced in the meantime), but you have to expect some missed >>> events if you're shoving any kind of dynamic marker into the code. The >>> main problem is if there's something still depending on the first 5 bytes >>> of the function (most likely if there's a loop head somewhere near the >>> top of the function). >>> >> >> I think we have to ensure no threads sleeping or being interrupted on >> the function when removing new function. How would you check it? >> > > Not sure I follow you. You'd never remove any code. But you'd only start You do, when you decide to stop tracing. He is not talking about the old function, that one, indeed will always be there, but what about the new one? When tracing stops we want to remove it and revert to using the old one... But perhaps you are suggesting that the new one, once loaded, stays there forever, that would work, but after several tracing sessions one would have to eventually reboot the machine due to many modules left loaded. - Arnaldo