Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750814AbWITBI6 (ORCPT ); Tue, 19 Sep 2006 21:08:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750817AbWITBI6 (ORCPT ); Tue, 19 Sep 2006 21:08:58 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:13739 "EHLO e31.co.us.ibm.com") by vger.kernel.org with ESMTP id S1750814AbWITBI5 (ORCPT ); Tue, 19 Sep 2006 21:08:57 -0400 Date: Wed, 20 Sep 2006 06:38:52 +0530 From: "S. P. Prasanna" To: Alan Cox Cc: Mathieu Desnoyers , Martin Bligh , 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 Subject: Re: [PATCH] Linux Kernel Markers Message-ID: <20060920010852.GA7469@in.ibm.com> Reply-To: prasanna@in.ibm.com References: <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> <1158710925.32598.120.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1158710925.32598.120.camel@localhost.localdomain> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1472 Lines: 40 Hi Alan, On Wed, Sep 20, 2006 at 01:08:45AM +0100, Alan Cox wrote: > 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". Are you referring to Intel erratum "unsynchronized cross-modifying code" - where it refers to the practice of modifying code on one processor where another has prefetched the unmodified version of the code. Thanks Prasanna > > 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. > -- Prasanna S.P. Linux Technology Center India Software Labs, IBM Bangalore Email: prasanna@in.ibm.com Ph: 91-80-41776329 - 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/