linux-kernel - Re: [PATCH v5 0/6] arm64: ftrace: fix incorrect output from stack tracer

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Date:	Mon, 9 Nov 2015 23:24:13 +0900
From:	Jungseok Lee <jungseoklee85@...il.com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	catalin.marinas@....com, will.deacon@....com, rostedt@...dmis.org,
	broonie@...nel.org, david.griego@...aro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/6] arm64: ftrace: fix incorrect output from stack tracer

On Nov 6, 2015, at 3:44 PM, AKASHI Takahiro wrote:

Hi Akashi,

> This is the fifth patch series for fixing stack tracer on arm64.
> The original issue was reported by Jungseok[1], and then I found more
> issues[2].
> 
> We don't have to care about the original issue because the root cause
> (patch "ARM64: unwind: Fix PC calculation") has been reverted in v4.3.
> 
> I address here all the issues and implement fixes described in [2] except
> for interrupt-triggered problems(II-3) and leaf function(II-5).  Recent
> discussions[3] about introducing a dedicated interrupt stack suggests that
> we may avoid walking through from an interrupt stack to a process stack.
> (So interrupt-stack patch is a prerequisite.)
> 
> Basically,
> patch1 is a proactive improvement of function_graph tracer. 
> patch2 corresponds to II-4(functions under function_graph tracer).
> patch3, 4 and 5 correspond to II-1(slurping stack) and II-2(differences
> between x86 and arm64).
> patch6 is a function prologue analyzer test. This won't attest
> the correctness of the functionality, but it can suggest that all
> the traced functions are treated properly by this function.
> (Please note that patch3 has already been queued in Steven's for-next.)
> 
> I tested the code with v4.3 + Jungseok's patch v5[4].

I've played this series with IRQ stack patch and it works well at least
on my system! In addition to this condition, I've run these changes without
IRQ stack since it is in progress. I could observe a single strange behavior,
minus stack size around elX_irq. Am I missing something?

My reproduction scenario is simple.

  $ sudo echo 1 > /proc/sys/kernel/stack_trace_enabled
  $ sudo echo function_graph > /sys/kernel/debug/tracing/current_tracer
  $ [ Run any workload ]
  $ sudo cat /sys/kernel/debug/tracing/stack_trace

Best Regards
Jungseok Lee
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