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