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