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/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# Starting with v5.1 this can be done with numbers, making it much faster:
24#
25# The old (slow) way, for kernels before v5.1.
26#
27# [old-way] # cat available_filter_functions > ~/full-file
28#
29# [old-way] *** Note ***  this process will take several minutes to update the
30# [old-way] filters. Setting multiple functions is an O(n^2) operation, and we
31# [old-way] are dealing with thousands of functions. So go have coffee, talk
32# [old-way] with your coworkers, read facebook. And eventually, this operation
33# [old-way] will end.
34#
35# The new way (using numbers) is an O(n) operation, and usually takes less than a second.
36#
37# seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file
38#
39# This will create a sequence of numbers that match the functions in
40# available_filter_functions, and when echoing in a number into the
41# set_ftrace_filter file, it will enable the corresponding function in
42# O(1) time. Making enabling all functions O(n) where n is the number of
43# functions to enable.
44#
45# For either the new or old way, the rest of the operations remain the same.
46#
47#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
48#  # cat ~/test-file > set_ftrace_filter
49#
50#  # echo function > current_tracer
51#
52# If it crashes, we know that ~/test-file has a bad function.
53#
54#   Reboot back to test kernel.
55#
56#     # cd /sys/kernel/tracing
57#     # mv ~/test-file ~/full-file
58#
59# If it didn't crash.
60#
61#     # echo nop > current_tracer
62#     # mv ~/non-test-file ~/full-file
63#
64# Get rid of the other test file from previous run (or save them off somewhere).
65#  # rm -f ~/test-file ~/non-test-file
66#
67# And start again:
68#
69#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
70#
71# The good thing is, because this cuts the number of functions in ~/test-file
72# by half, the cat of it into set_ftrace_filter takes half as long each
73# iteration, so don't talk so much at the water cooler the second time.
74#
75# Eventually, if you did this correctly, you will get down to the problem
76# function, and all we need to do is to notrace it.
77#
78# The way to figure out if the problem function is bad, just do:
79#
80#  # echo <problem-function> > set_ftrace_notrace
81#  # echo > set_ftrace_filter
82#  # echo function > current_tracer
83#
84# And if it doesn't crash, we are done.
85#
86# If it does crash, do this again (there's more than one problem function)
87# but you need to echo the problem function(s) into set_ftrace_notrace before
88# enabling function tracing in the above steps. Or if you can compile the
89# kernel, annotate the problem functions with "notrace" and start again.
90#
91
92
93if [ $# -ne 3 ]; then
94  echo 'usage: ftrace-bisect full-file test-file  non-test-file'
95  exit
96fi
97
98full=$1
99test=$2
100nontest=$3
101
102x=`cat $full | wc -l`
103if [ $x -eq 1 ]; then
104	echo "There's only one function left, must be the bad one"
105	cat $full
106	exit 0
107fi
108
109let x=$x/2
110let y=$x+1
111
112if [ ! -f $full ]; then
113	echo "$full does not exist"
114	exit 1
115fi
116
117if [ -f $test ]; then
118	echo -n "$test exists, delete it? [y/N]"
119	read a
120	if [ "$a" != "y" -a "$a" != "Y" ]; then
121		exit 1
122	fi
123fi
124
125if [ -f $nontest ]; then
126	echo -n "$nontest exists, delete it? [y/N]"
127	read a
128	if [ "$a" != "y" -a "$a" != "Y" ]; then
129		exit 1
130	fi
131fi
132
133sed -ne "1,${x}p" $full > $test
134sed -ne "$y,\$p" $full > $nontest
135