ftrace/scripts: Add helper script to bisect function tracing problem functions

[mirror_ubuntu-bionic-kernel.git] / scripts / tracing / ftrace-bisect.sh

diff --git a/scripts/tracing/ftrace-bisect.sh b/scripts/tracing/ftrace-bisect.sh
new file mode 100755 (executable)
index 0000000..9ff8ac5
--- /dev/null
+++ b/scripts/tracing/ftrace-bisect.sh
@@ -0,0 +1,115 @@
+#!/bin/bash
+#
+# Here's how to use this:
+#
+# This script is used to help find functions that are being traced by function
+# tracer or function graph tracing that causes the machine to reboot, hang, or
+# crash. Here's the steps to take.
+#
+# First, determine if function tracing is working with a single function:
+#
+#   (note, if this is a problem with function_graph tracing, then simply
+#    replace "function" with "function_graph" in the following steps).
+#
+#  # cd /sys/kernel/debug/tracing
+#  # echo schedule > set_ftrace_filter
+#  # echo function > current_tracer
+#
+# If this works, then we know that something is being traced that shouldn't be.
+#
+#  # echo nop > current_tracer
+#
+#  # cat available_filter_functions > ~/full-file
+#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
+#  # cat ~/test-file > set_ftrace_filter
+#
+# *** Note *** this will take several minutes. Setting multiple functions is
+# an O(n^2) operation, and we are dealing with thousands of functions. So go
+# have  coffee, talk with your coworkers, read facebook. And eventually, this
+# operation will end.
+#
+#  # echo function > current_tracer
+#
+# If it crashes, we know that ~/test-file has a bad function.
+#
+#   Reboot back to test kernel.
+#
+#     # cd /sys/kernel/debug/tracing
+#     # mv ~/test-file ~/full-file
+#
+# If it didn't crash.
+#
+#     # echo nop > current_tracer
+#     # mv ~/non-test-file ~/full-file
+#
+# Get rid of the other test file from previous run (or save them off somewhere).
+#  # rm -f ~/test-file ~/non-test-file
+#
+# And start again:
+#
+#  # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
+#
+# The good thing is, because this cuts the number of functions in ~/test-file
+# by half, the cat of it into set_ftrace_filter takes half as long each
+# iteration, so don't talk so much at the water cooler the second time.
+#
+# Eventually, if you did this correctly, you will get down to the problem
+# function, and all we need to do is to notrace it.
+#
+# The way to figure out if the problem function is bad, just do:
+#
+#  # echo <problem-function> > set_ftrace_notrace
+#  # echo > set_ftrace_filter
+#  # echo function > current_tracer
+#
+# And if it doesn't crash, we are done.
+#
+# If it does crash, do this again (there's more than one problem function)
+# but you need to echo the problem function(s) into set_ftrace_notrace before
+# enabling function tracing in the above steps. Or if you can compile the
+# kernel, annotate the problem functions with "notrace" and start again.
+#
+
+
+if [ $# -ne 3 ]; then
+  echo 'usage: ftrace-bisect full-file test-file  non-test-file'
+  exit
+fi
+
+full=$1
+test=$2
+nontest=$3
+
+x=`cat $full | wc -l`
+if [ $x -eq 1 ]; then
+       echo "There's only one function left, must be the bad one"
+       cat $full
+       exit 0
+fi
+
+let x=$x/2
+let y=$x+1
+
+if [ ! -f $full ]; then
+       echo "$full does not exist"
+       exit 1
+fi
+
+if [ -f $test ]; then
+       echo -n "$test exists, delete it? [y/N]"
+       read a
+       if [ "$a" != "y" -a "$a" != "Y" ]; then
+               exit 1
+       fi
+fi
+
+if [ -f $nontest ]; then
+       echo -n "$nontest exists, delete it? [y/N]"
+       read a
+       if [ "$a" != "y" -a "$a" != "Y" ]; then
+               exit 1
+       fi
+fi
+
+sed -ne "1,${x}p" $full > $test
+sed -ne "$y,\$p" $full > $nontest