From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755085AbZIMRrb (ORCPT ); Sun, 13 Sep 2009 13:47:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754951AbZIMRr1 (ORCPT ); Sun, 13 Sep 2009 13:47:27 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:45689 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751429AbZIMRr0 (ORCPT ); Sun, 13 Sep 2009 13:47:26 -0400 Subject: Re: [PATCH 2/4] tracing/function-graph: x86_64 stack allocation cleanup From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Peter Zijlstra , Li Zefan , Jiri Olsa In-Reply-To: <20090913170517.GB4859@nowhere> References: <20090913030543.204871396@goodmis.org> <20090913030616.992539807@goodmis.org> <20090913170517.GB4859@nowhere> Content-Type: text/plain Organization: Kihon Technologies Inc. Date: Sun, 13 Sep 2009 13:47:27 -0400 Message-Id: <1252864047.26049.923.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.26.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2009-09-13 at 19:05 +0200, Frederic Weisbecker wrote: > On Sat, Sep 12, 2009 at 11:05:45PM -0400, Steven Rostedt wrote: > > From: Jiri Olsa > > > > Only 24 bytes needs to be reserved on the stack for the function graph > > tracer on x86_64. > > > > Signed-off-by: Jiri Olsa > > LKML-Reference: <20090729085837.GB4998@jolsa.lab.eng.brq.redhat.com> > > Signed-off-by: Steven Rostedt > > --- > > arch/x86/kernel/entry_64.S | 6 +++--- > > 1 files changed, 3 insertions(+), 3 deletions(-) > > > > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > > index c251be7..d59fe32 100644 > > --- a/arch/x86/kernel/entry_64.S > > +++ b/arch/x86/kernel/entry_64.S > > @@ -146,7 +146,7 @@ ENTRY(ftrace_graph_caller) > > END(ftrace_graph_caller) > > > > GLOBAL(return_to_handler) > > - subq $80, %rsp > > + subq $24, %rsp > > > That's theoretically a good fix. > > But Steve, do you remember the weird issues we had while only > saving the theoretically strict needed stack space here? > > It made the function graph tracer crashing in x86-64, and we > never found out why we needed to save more stack than needed. > > Sorry that may sound like a FUD message but I can't explain > the reason of this, and I fear we may met it again. > > Well, at least that may help us finding out the real resons of > such crashes, but... I did not forget about them, and that's the reason that I did not apply them in the beginning. But that was long ago, and we fixed lots of issues. I remember hitting crashes with the patch too, but I've applied this and ran it on those same machines and I no longer get those crashes. Thus, my thinking is that we already fixed the bug that was causing it. Only way to know for sure is to apply it and let it out into the wild ;-) -- Steve