linux-kernel - [PATCH] x86: don't save unreliable stack trace entries

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Date:	Fri, 22 Feb 2008 19:44:05 +0100
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>, Ingo Molnar <mingo@...e.hu>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86: don't save unreliable stack trace entries

I find the following patch to make saved stack traces so much easier to
decipher. There might be other uses of save_stack_trace() that I am not
aware of, though. Also, I suggest changing the underlying struct
stack_trace to include the reliable/unreliable information. This, however,
requires all users of save_stack_trace() and all arches saving this
information to change.

Kind regards,
Vegard Nossum

 From 5edfd896c5f0d728111df3d8cae729a375f29d3c Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum@...il.com>
Date: Fri, 22 Feb 2008 19:23:58 +0100
Subject: [PATCH] x86: don't save unreliable stack trace entries

Currently, there is no way for print_stack_trace() to determine whether a
given stack trace entry was deemed reliable or not, simply because
save_stack_trace() does not record this information. (Perhaps needless to
say, this makes the saved stack traces A LOT harder to read, and probably
with no other benefits, since debugging features that use
save_stack_trace() most likely also require frame pointers, etc.)

This patch reverts to the old behaviour of only recording the reliable trace
entries for saved stack traces.

Signed-off-by: Vegard Nossum <vegardno@....uio.no>
---
  arch/x86/kernel/stacktrace.c |    4 ++++
  1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 02f0f61..c28c342 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -25,6 +25,8 @@ static int save_stack_stack(void *data, char *name)
  static void save_stack_address(void *data, unsigned long addr, int reliable)
  {
  	struct stack_trace *trace = data;
+	if (!reliable)
+		return;
  	if (trace->skip > 0) {
  		trace->skip--;
  		return;
@@ -37,6 +39,8 @@ static void
  save_stack_address_nosched(void *data, unsigned long addr, int reliable)
  {
  	struct stack_trace *trace = (struct stack_trace *)data;
+	if (!reliable)
+		return;
  	if (in_sched_functions(addr))
  		return;
  	if (trace->skip > 0) {
-- 
1.5.3.8

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