linux-kernel - Re: [PATCH] acpi: fix incompatibility with mcount-based function graph tracing

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Message-ID: <20170327140843.fx5y32rnc3mqiyke@treble>
Date:   Mon, 27 Mar 2017 09:08:43 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] acpi: fix incompatibility with mcount-based function
 graph tracing

On Sat, Mar 25, 2017 at 02:20:11PM +0100, Rafael J. Wysocki wrote:
> On Friday, March 24, 2017 02:41:14 PM Steven Rostedt wrote:
> > On Fri, 24 Mar 2017 13:12:54 -0500
> > Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > 
> > 
> > > Instead I was able to "fix" it by ignoring ftrace calls in real mode:
> > > 
> > > -----
> > > index 8f3d9cf..5c0d0c6 100644
> > > --- a/arch/x86/kernel/ftrace.c
> > > +++ b/arch/x86/kernel/ftrace.c
> > > @@ -983,6 +983,9 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
> > >  	unsigned long return_hooker = (unsigned long)
> > >  				&return_to_handler;
> > >  
> > > +	if (__builtin_return_address(0) < TASK_SIZE_MAX)
> > > +		return;
> > > +
> > >  	if (unlikely(ftrace_graph_is_dead()))
> > >  		return;
> > > ---------------
> > > 
> > > I'm not sure what the best fix should really be.  A few ideas off the
> > > top of my head:
> > > 
> > > - A real mode check similar to the above (except it should probably be
> > >   more precise)
> > 
> > The real mode check hack may be good enough for now. Make sure that
> > it's commented well.
> 
> Agreed.

Just to clarify, there are two bugs related to function graph tracing
and suspend/resume.  The original patch in this thread (which removes
'-Os' from the acpi Makefile) is still needed.

-- 
Josh