From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754228AbcHAQsB (ORCPT <rfc822;w@1wt.eu>);
	Mon, 1 Aug 2016 12:48:01 -0400
Received: from mx1.redhat.com ([209.132.183.28]:39422 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1754028AbcHAQrw (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 1 Aug 2016 12:47:52 -0400
Date: Mon, 1 Aug 2016 10:59:03 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>, Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Byungchul Park <byungchul.park@lge.com>
Subject: Re: [PATCH 05/19] x86/dumpstack: fix function graph tracing stack
 dump reliability issues
Message-ID: <20160801155903.wuclx6oys6v4sa66@treble>
References: <cover.1469136008.git.jpoimboe@redhat.com>
 <ee70f40bd7773f2bc77b9ce55869163cce2aa9f2.1469136008.git.jpoimboe@redhat.com>
 <20160729185521.62a5cd2a@gandalf.local.home>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20160729185521.62a5cd2a@gandalf.local.home>
User-Agent: Mutt/1.6.0.1 (2016-04-01)
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 01 Aug 2016 15:59:06 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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@goodmis.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.

-- 
Josh