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