From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753551AbaB0Qhi (ORCPT ); Thu, 27 Feb 2014 11:37:38 -0500 Received: from mail-we0-f171.google.com ([74.125.82.171]:57213 "EHLO mail-we0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752677AbaB0Qhg (ORCPT ); Thu, 27 Feb 2014 11:37:36 -0500 Date: Thu, 27 Feb 2014 17:37:32 +0100 From: Frederic Weisbecker To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Peter Zijlstra , Mathieu Desnoyers , stable@vger.kernel.org, Petr Mladek Subject: Re: [RFA][PATCH 2/5] ftrace/x86: One more missing sync after fixup of function modification failure Message-ID: <20140227163731.GC19580@localhost.localdomain> References: <20140227154616.703252665@goodmis.org> <20140227154923.103932155@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140227154923.103932155@goodmis.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 27, 2014 at 10:46:18AM -0500, Steven Rostedt wrote: > [Request for Ack] > > From: Petr Mladek > > If a failure occurs while modifying ftrace function, it bails out and will > remove the tracepoints to be back to what the code originally was. > > There is missing the final sync run across the CPUs after the fix up is done > and before the ftrace int3 handler flag is reset. So IIUC the risk is that other CPUs may spuriously ignore non-ftrace traps if we don't sync the other cores after reverting the int3 before decrementing the modifying_ftrace_code counter? > > Link: http://lkml.kernel.org/r/1393258342-29978-2-git-send-email-pmladek@suse.cz > > Fixes: 8a4d0a687a5 "ftrace: Use breakpoint method to update ftrace caller" > Cc: stable@vger.kernel.org # 3.5+ > Signed-off-by: Petr Mladek > Signed-off-by: Steven Rostedt > --- > arch/x86/kernel/ftrace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 6b566c8..69885e2 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -660,8 +660,8 @@ ftrace_modify_code(unsigned long ip, unsigned const char *old_code, > ret = -EPERM; > goto out; > } > - run_sync(); > out: > + run_sync(); > return ret; > > fail_update: This could be further optimized by rather calling run_sync() in the end of the fail_update block (after the probe_kernel_write revert) otherwise even failure on setting the break will result in run_sync(), which doesn't appear to be needed. But that's really just nitpicking as it's a rare failure codepath and shouldn't hurt. In any case, the fix looks correct. Acked-by: Frederic Weisbecker > -- > 1.8.5.3 > >