Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754520AbYHSClS (ORCPT ); Mon, 18 Aug 2008 22:41:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752571AbYHSClE (ORCPT ); Mon, 18 Aug 2008 22:41:04 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:37821 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752527AbYHSClD (ORCPT ); Mon, 18 Aug 2008 22:41:03 -0400 Date: Mon, 18 Aug 2008 22:41:00 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Benjamin Herrenschmidt cc: Scott Wood , Eran Liberty , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Steven Rostedt , "Paul E. McKenney" Subject: Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3) In-Reply-To: <1219113549.8062.13.camel@pasglop> Message-ID: References: <48591941.4070408@extricom.com> <48A92E15.2080709@extricom.com> <48A9901B.1080900@redhat.com> <20080818154746.GA26835@Krystal> <48A9AFA7.8080508@freescale.com> <1219110814.8062.2.camel@pasglop> <1219113549.8062.13.camel@pasglop> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1383 Lines: 50 On Tue, 19 Aug 2008, Benjamin Herrenschmidt wrote: > > > Hmm, this was originally copied from x86, where we did a cmpxchg, but that > > is probably not needed since all of this is done in kstop_machine. Also, > > only the "get" is needed. If we don't fault there, we wont fault on the > > put (unless we have permissions wrong, and that would be a bug). > > Would it ? How do we make sure the kernel text is mapped writeable ? We map it writeable if FTRACE is enabled. > > > So are you recommending something like > > > > int cmd; > > > > if (__get_user(cmd, ip)) > > goto fault; > > > > if (cmd != old) > > goto not_same; > > > > WARN_ON_ONCE(__put_user(cmd, ip)); > > > > If we did this, we could probably put this into the generic code: > > That would work I suppose, I'll give it a try. > > > if (copy_from_user(cmd, ip, ARCH_CALL_SIZE)) > > goto fault; > > > > if (memcmp(cmd, old, ARCH_CALL_SIZE) != 0) > > goto not_same; > > > > WARN_ON_ONCE(copy_to_user(cmd, ip, ARCH_CALL_SIZE)); > > You need the __ variants or the access_ok() checks will bite > you bad. Ah, good point ;-) -- Steve -- 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/