From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752462AbZIMRzK (ORCPT ); Sun, 13 Sep 2009 13:55:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751287AbZIMRzH (ORCPT ); Sun, 13 Sep 2009 13:55:07 -0400 Received: from fg-out-1718.google.com ([72.14.220.155]:58703 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750895AbZIMRzF (ORCPT ); Sun, 13 Sep 2009 13:55:05 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=GFp99faLMevuMsVXBp4vLR2NaqJtiAsmjQ2zcz3FFB4kniDCSHRr/omiybkOeLnKXt mLHJNclCQpGJILigrWOt7iP+1QXMN/g2dE+ne0HlD9AQ60mF9mi84JruCzg0EE930h6L Kz/z43BxdXLvi9ZWaUq0+c+YtCWg/bdXqdt2Y= Date: Sun, 13 Sep 2009 19:55:05 +0200 From: Frederic Weisbecker To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Peter Zijlstra , Li Zefan , Jiri Olsa Subject: Re: [PATCH 2/4] tracing/function-graph: x86_64 stack allocation cleanup Message-ID: <20090913175504.GC5030@nowhere> References: <20090913030543.204871396@goodmis.org> <20090913030616.992539807@goodmis.org> <20090913170517.GB4859@nowhere> <1252864047.26049.923.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1252864047.26049.923.camel@gandalf.stny.rr.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 13, 2009 at 01:47:27PM -0400, Steven Rostedt wrote: > 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 ;-) Ok, fine then :)