scripts/tracing/ftrace-bisect.sh

0001 #!/bin/bash
0002 # SPDX-License-Identifier: GPL-2.0
0003 #
0004 # Here's how to use this:
0005 #
0006 # This script is used to help find functions that are being traced by function
0007 # tracer or function graph tracing that causes the machine to reboot, hang, or
0008 # crash. Here's the steps to take.
0009 #
0010 # First, determine if function tracing is working with a single function:
0011 #
0012 #   (note, if this is a problem with function_graph tracing, then simply
0013 #    replace "function" with "function_graph" in the following steps).
0014 #
0015 #  # cd /sys/kernel/debug/tracing
0016 #  # echo schedule > set_ftrace_filter
0017 #  # echo function > current_tracer
0018 #
0019 # If this works, then we know that something is being traced that shouldn't be.
0020 #
0021 #  # echo nop > current_tracer
0022 #
0023 #  # cat available_filter_functions > ~/full-file
0024 #  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
0025 #  # cat ~/test-file > set_ftrace_filter
0026 #
0027 # *** Note *** this will take several minutes. Setting multiple functions is
0028 # an O(n^2) operation, and we are dealing with thousands of functions. So go
0029 # have  coffee, talk with your coworkers, read facebook. And eventually, this
0030 # operation will end.
0031 #
0032 #  # echo function > current_tracer
0033 #
0034 # If it crashes, we know that ~/test-file has a bad function.
0035 #
0036 #   Reboot back to test kernel.
0037 #
0038 #     # cd /sys/kernel/debug/tracing
0039 #     # mv ~/test-file ~/full-file
0040 #
0041 # If it didn't crash.
0042 #
0043 #     # echo nop > current_tracer
0044 #     # mv ~/non-test-file ~/full-file
0045 #
0046 # Get rid of the other test file from previous run (or save them off somewhere).
0047 #  # rm -f ~/test-file ~/non-test-file
0048 #
0049 # And start again:
0050 #
0051 #  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
0052 #
0053 # The good thing is, because this cuts the number of functions in ~/test-file
0054 # by half, the cat of it into set_ftrace_filter takes half as long each
0055 # iteration, so don't talk so much at the water cooler the second time.
0056 #
0057 # Eventually, if you did this correctly, you will get down to the problem
0058 # function, and all we need to do is to notrace it.
0059 #
0060 # The way to figure out if the problem function is bad, just do:
0061 #
0062 #  # echo <problem-function> > set_ftrace_notrace
0063 #  # echo > set_ftrace_filter
0064 #  # echo function > current_tracer
0065 #
0066 # And if it doesn't crash, we are done.
0067 #
0068 # If it does crash, do this again (there's more than one problem function)
0069 # but you need to echo the problem function(s) into set_ftrace_notrace before
0070 # enabling function tracing in the above steps. Or if you can compile the
0071 # kernel, annotate the problem functions with "notrace" and start again.
0072 #
0073
0074
0075 if [ $# -ne 3 ]; then
0076   echo 'usage: ftrace-bisect full-file test-file  non-test-file'
0077   exit
0078 fi
0079
0080 full=$1
0081 test=$2
0082 nontest=$3
0083
0084 x=`cat $full | wc -l`
0085 if [ $x -eq 1 ]; then
0086         echo "There's only one function left, must be the bad one"
0087         cat $full
0088         exit 0
0089 fi
0090
0091 let x=$x/2
0092 let y=$x+1
0093
0094 if [ ! -f $full ]; then
0095         echo "$full does not exist"
0096         exit 1
0097 fi
0098
0099 if [ -f $test ]; then
0100         echo -n "$test exists, delete it? [y/N]"
0101         read a
0102         if [ "$a" != "y" -a "$a" != "Y" ]; then
0103                 exit 1
0104         fi
0105 fi
0106
0107 if [ -f $nontest ]; then
0108         echo -n "$nontest exists, delete it? [y/N]"
0109         read a
0110         if [ "$a" != "y" -a "$a" != "Y" ]; then
0111                 exit 1
0112         fi
0113 fi
0114
0115 sed -ne "1,${x}p" $full > $test
0116 sed -ne "$y,\$p" $full > $nontest