scripts/tracing/ftrace-bisect.sh

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