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 11:24:59 -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 Fri, Jul 29, 2016 at 06:55:21PM -0400, Steven Rostedt wrote:
> > @@ -108,18 +97,23 @@ print_context_stack(struct task_struct *task,
> >  		stack = (unsigned long *)task_stack_page(task);
> >  
> >  	while (valid_stack_ptr(task, stack, sizeof(*stack), end)) {
> > -		unsigned long addr;
> > +		unsigned long addr = *stack;
> >  
> >  		addr = *stack;
> >  		if (__kernel_text_address(addr)) {
> > +			int reliable = 0;
> > +			unsigned long real_addr;
> > +
> >  			if ((unsigned long) stack == bp + sizeof(long)) {
> > -				ops->address(data, addr, 1);
> > +				reliable = 1;
> >  				frame = frame->next_frame;
> >  				bp = (unsigned long) frame;
> > -			} else {
> > -				ops->address(data, addr, 0);
> >  			}
> > -			print_ftrace_graph_addr(addr, data, ops, task, graph);
> > +
> > +			real_addr = ftrace_graph_ret_addr(task, graph, addr);
> > +			if (addr != real_addr)
> > +				ops->address(data, addr, 0);
> > +			ops->address(data, real_addr, reliable);
> 
> Note this changes behavior, as the original code had the ret_to_handler
> first. This makes it second. (I fixed this below).

Hm, as far as I can tell this actually keeps the original behavior.  The
"unreliable" ret_to_handler is still printed first, no?

-- 
Josh