1#!/bin/bash
2# SPDX-License-Identifier: GPL-2.0
3#
4# Here's how to use this:
5#
6# This script is used to help find functions that are being traced by function
7# tracer or function graph tracing that causes the machine to reboot, hang, or
8# crash. Here's the steps to take.
9#
10# First, determine if function tracing is working with a single function:
11#
12#   (note, if this is a problem with function_graph tracing, then simply
13#    replace "function" with "function_graph" in the following steps).
14#
15#  # cd /sys/kernel/debug/tracing
16#  # echo schedule > set_ftrace_filter
17#  # echo function > current_tracer
18#
19# If this works, then we know that something is being traced that shouldn't be.
20#
21#  # echo nop > current_tracer
22#
23#  # cat available_filter_functions > ~/full-file
24#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
25#  # cat ~/test-file > set_ftrace_filter
26#
27# *** Note *** this will take several minutes. Setting multiple functions is
28# an O(n^2) operation, and we are dealing with thousands of functions. So go
29# have  coffee, talk with your coworkers, read facebook. And eventually, this
30# operation will end.
31#
32#  # echo function > current_tracer
33#
34# If it crashes, we know that ~/test-file has a bad function.
35#
36#   Reboot back to test kernel.
37#
38#     # cd /sys/kernel/debug/tracing
39#     # mv ~/test-file ~/full-file
40#
41# If it didn't crash.
42#
43#     # echo nop > current_tracer
44#     # mv ~/non-test-file ~/full-file
45#
46# Get rid of the other test file from previous run (or save them off somewhere).
47#  # rm -f ~/test-file ~/non-test-file
48#
49# And start again:
50#
51#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
52#
53# The good thing is, because this cuts the number of functions in ~/test-file
54# by half, the cat of it into set_ftrace_filter takes half as long each
55# iteration, so don't talk so much at the water cooler the second time.
56#
57# Eventually, if you did this correctly, you will get down to the problem
58# function, and all we need to do is to notrace it.
59#
60# The way to figure out if the problem function is bad, just do:
61#
62#  # echo <problem-function> > set_ftrace_notrace
63#  # echo > set_ftrace_filter
64#  # echo function > current_tracer
65#
66# And if it doesn't crash, we are done.
67#
68# If it does crash, do this again (there's more than one problem function)
69# but you need to echo the problem function(s) into set_ftrace_notrace before
70# enabling function tracing in the above steps. Or if you can compile the
71# kernel, annotate the problem functions with "notrace" and start again.
72#
73
74
75if [ $# -ne 3 ]; then
76  echo 'usage: ftrace-bisect full-file test-file  non-test-file'
77  exit
78fi
79
80full=$1
81test=$2
82nontest=$3
83
84x=`cat $full | wc -l`
85if [ $x -eq 1 ]; then
86	echo "There's only one function left, must be the bad one"
87	cat $full
88	exit 0
89fi
90
91let x=$x/2
92let y=$x+1
93
94if [ ! -f $full ]; then
95	echo "$full does not exist"
96	exit 1
97fi
98
99if [ -f $test ]; then
100	echo -n "$test exists, delete it? [y/N]"
101	read a
102	if [ "$a" != "y" -a "$a" != "Y" ]; then
103		exit 1
104	fi
105fi
106
107if [ -f $nontest ]; then
108	echo -n "$nontest exists, delete it? [y/N]"
109	read a
110	if [ "$a" != "y" -a "$a" != "Y" ]; then
111		exit 1
112	fi
113fi
114
115sed -ne "1,${x}p" $full > $test
116sed -ne "$y,\$p" $full > $nontest
117