linux-kernel - Re: [PATCH 15/19] x86/dumpstack: convert show_trace_log

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Message-ID: <20160721214901.GT2279@X58A-UD3R>
Date:	Fri, 22 Jul 2016 06:49:01 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
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>,
	Steven Rostedt <rostedt@...dmis.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 15/19] x86/dumpstack: convert show_trace_log_lvl() to the
 new unwinder

On Thu, Jul 21, 2016 at 04:21:52PM -0500, Josh Poimboeuf wrote:
> Convert show_trace_log_lvl() to the new unwinder.  dump_trace() has been
> deprecated.
> 
> show_trace_log_lvl() is special compared to other users of the unwinder.
> It's the only place where both reliable *and* unreliable addresses are
> needed.  With frame pointers enabled, most stack walking code doesn't
> want to know about unreliable addresses.  But in this case, when we're
> dumping the stack to the console because something presumably went
> wrong, the unreliable addresses are useful:
> 
> - They show stale data on the stack which can provide useful clues.
> 
> - If something goes wrong with the unwinder, or if frame pointers are
>   corrupt or missing, all the stack addresses still get shown.
> 
> So in order to show all addresses on the stack, and at the same time
> figure out which addresses are reliable, we have to do the scanning and
> the unwinding in parallel.
> 
> The scanning is done with the help of get_stack_info() to traverse the
> stacks.  The unwinding is done separately by the new unwinder.
> 
> In theory we could simplify show_trace_log_lvl() by instead pushing some
> of this logic into the unwind code.  But then we would need some kind of
> "fake" frame logic in the unwinder which would add a lot of complexity
> and wouldn't be worth it in order to support only one user.
> 
> Another benefit of this approach is that once we have a DWARF unwinder,
> we should be able to just plug it in with minimal impact to this code.
> 
> Another change here is that callers of show_trace_log_lvl() don't need
> to provide the 'bp' argument.  The unwinder already finds the relevant
> frame pointer by unwinding until it reaches the first frame after the
> provided stack pointer.

Hello,

You seem to have changed a lot of code with which I dealt in another patch.
I might be supposed to wait until yours will be done. I need to check yours
at first anyway.