scripts/tracing/ftrace-bisect.sh

   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
  75 if [ $# -ne 3 ]; then
  76   echo 'usage: ftrace-bisect full-file test-file  non-test-file'
  77   exit
  78 fi
  79
  80 full=$1
  81 test=$2
  82 nontest=$3
  83
  84 x=`cat $full | wc -l`
  85 if [ $x -eq 1 ]; then
  86         echo "There's only one function left, must be the bad one"
  87         cat $full
  88         exit 0
  89 fi
  90
  91 let x=$x/2
  92 let y=$x+1
  93
  94 if [ ! -f $full ]; then
  95         echo "$full does not exist"
  96         exit 1
  97 fi
  98
  99 if [ -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
 105 fi
 106
 107 if [ -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
 113 fi
 114
 115 sed -ne "1,${x}p" $full > $test
 116 sed -ne "$y,\$p" $full > $nontest