Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750811AbWISXqq (ORCPT ); Tue, 19 Sep 2006 19:46:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750819AbWISXqq (ORCPT ); Tue, 19 Sep 2006 19:46:46 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:54167 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S1750811AbWISXqp (ORCPT ); Tue, 19 Sep 2006 19:46:45 -0400 Subject: Re: [PATCH] Linux Kernel Markers From: Alan Cox To: Mathieu Desnoyers Cc: Martin Bligh , prasanna@in.ibm.com, Andrew Morton , "Frank Ch. Eigler" , Ingo Molnar , Paul Mundt , linux-kernel , Jes Sorensen , Tom Zanussi , Richard J Moore , Michel Dagenais , Christoph Hellwig , Greg Kroah-Hartman , Thomas Gleixner , William Cohen , ltt-dev@shafik.org, systemtap@sources.redhat.com In-Reply-To: <20060919175405.GC26339@Krystal> References: <20060918234502.GA197@Krystal> <20060919081124.GA30394@elte.hu> <451008AC.6030006@google.com> <20060919154612.GU3951@redhat.com> <4510151B.5070304@google.com> <20060919093935.4ddcefc3.akpm@osdl.org> <45101DBA.7000901@google.com> <20060919063821.GB23836@in.ibm.com> <45102641.7000101@google.com> <20060919175405.GC26339@Krystal> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 20 Sep 2006 01:08:45 +0100 Message-Id: <1158710925.32598.120.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.2 (2.6.2-1.fc5.5) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1025 Lines: 24 Ar Maw, 2006-09-19 am 13:54 -0400, ysgrifennodd Mathieu Desnoyers: > Very good idea.. However, overwriting the second instruction with a jump could > be dangerous on preemptible and SMP kernels, because we never know if a thread > has an IP in any of its contexts that would return exactly at the middle of the > jump. No: on x86 it is the *same* case for all of these even writing an int3. One byte or a megabyte, You MUST ensure that every CPU executes a serializing instruction before it hits code that was modified by another processor. Otherwise you get CPU errata and the CPU produces results which vendors like to describe as "undefined". Thus you have to serialize, and if you are serializing it really doesn't matter if you write a byte, a paragraph or a page. Alan - 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/