From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755481AbaCCWph (ORCPT ); Mon, 3 Mar 2014 17:45:37 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.228]:26608 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753236AbaCCWpg (ORCPT ); Mon, 3 Mar 2014 17:45:36 -0500 Date: Mon, 3 Mar 2014 17:45:32 -0500 From: Steven Rostedt To: Greg Kroah-Hartman Cc: Linus Torvalds , LKML Subject: Re: Question about -rc and stable patches Message-ID: <20140303174532.7cb8f31e@gandalf.local.home> In-Reply-To: <20140303224104.GA26031@kroah.com> References: <20140303172806.4486f65a@gandalf.local.home> <20140303224104.GA26031@kroah.com> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 3 Mar 2014 14:41:04 -0800 Greg Kroah-Hartman wrote: > On Mon, Mar 03, 2014 at 05:28:06PM -0500, Steven Rostedt wrote: > > Hi Linus and Greg, > > > > Recently I have been sent patches that fix a bug in the enabling of > > ftrace function tracer, where if something goes wrong with the > > enabling (or disabling), it can cause a crash of the computer. > > > > Now, my question is, the bug requires something to go wrong at a point > > where I've never seen it go wrong before. But if you inject a problem > > (code that makes it fail on the 1000th iteration), sure enough, the > > recovery is not correct and the machine crashes. > > What exactly do you mean by "inject a problem"? What kind of > permissions does that require to do? Modify kernel source ;-) Basically, I added this patch to the kernel, compiled it, enabled function tracing, and it crashed: diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 8cabf63..9f354e5 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -586,6 +586,9 @@ void ftrace_replace_code(int enable) for_ftrace_rec_iter(iter) { rec = ftrace_rec_iter_record(iter); + if (count == 1000) + ret = -EPERM; + else ret = add_breakpoints(rec, enable); if (ret) goto remove_breakpoints; Not something that can be done from normal operations. -- Steve