linux-kernel - Re: [PATCH 05/19] x86/dumpstack: fix function graph tracing stack dump reliability issues

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Date:	Mon, 1 Aug 2016 11:19:07 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Byungchul Park <byungchul.park@....com>
Subject: Re: [PATCH 05/19] x86/dumpstack: fix function graph tracing stack
 dump reliability issues

On Mon, Aug 01, 2016 at 12:05:41PM -0400, Steven Rostedt wrote:
> On Mon, 1 Aug 2016 10:59:03 -0500
> Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> > On Fri, Jul 29, 2016 at 06:55:21PM -0400, Steven Rostedt wrote:
> > > Here's my patch that should be applied on top.
> > > 
> > > Maybe add a Signed-off-by: Steven Rostedt <rostedt@...dmis.org> along
> > > with your SOB. But you should remain Author.  
> > 
> > [...]
> > 
> > > @@ -123,13 +124,16 @@ print_context_stack_bp(struct task_struc
> > >  
> > >  	while (valid_stack_ptr(task, ret_addr, sizeof(*ret_addr), end)) {
> > >  		unsigned long addr = *ret_addr;
> > > +		unsigned long real_addr;
> > >  
> > >  		if (!__kernel_text_address(addr))
> > >  			break;
> > >  
> > > -		addr = ftrace_graph_ret_addr(task, graph, addr);
> > > -		if (ops->address(data, addr, 1))
> > > +		real_addr = ftrace_graph_ret_addr(task, graph, addr);
> > > +		if (ops->address(data, real_addr, 1))
> > >  			break;
> > > +		if (real_addr != addr)
> > > +			ops->address(data, addr, 0);
> > >  		frame = frame->next_frame;
> > >  		ret_addr = &frame->return_address;
> > >  	}  
> > 
> > Actually this hunk isn't needed because all users of
> > print_context_stack_bp() only care about "reliable" addresses.  With
> > frame pointers enabled, the only place "unreliable" addresses are used
> > is in show_trace_log_lvl() -- and it uses the print_context_stack()
> > callback.
> > 
> > I rely on that fact in the new frame pointer unwind code: it only
> > reports reliable addresses.
> > 
> 
> Can you make this a separate patch then. Before this one, and explain
> why it isn't needed in the change log. I rather have the current patch
> not make such a change in logic.

Sure, I'll do that.

-- 
Josh