name : ftrace-bisect.sh #!/bin/bash # SPDX-License-Identifier: GPL-2.0 # # 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/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 # # Starting with v5.1 this can be done with numbers, making it much faster: # # The old (slow) way, for kernels before v5.1. # # [old-way] # cat available_filter_functions > ~/full-file # # [old-way] *** Note *** this process will take several minutes to update the # [old-way] filters. Setting multiple functions is an O(n^2) operation, and we # [old-way] are dealing with thousands of functions. So go have coffee, talk # [old-way] with your coworkers, read facebook. And eventually, this operation # [old-way] will end. # # The new way (using numbers) is an O(n) operation, and usually takes less than a second. # # seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file # # This will create a sequence of numbers that match the functions in # available_filter_functions, and when echoing in a number into the # set_ftrace_filter file, it will enable the corresponding function in # O(1) time. Making enabling all functions O(n) where n is the number of # functions to enable. # # For either the new or old way, the rest of the operations remain the same. # # # ftrace-bisect ~/full-file ~/test-file ~/non-test-file # # cat ~/test-file > set_ftrace_filter # # # echo function > current_tracer # # If it crashes, we know that ~/test-file has a bad function. # # Reboot back to test kernel. # # # cd /sys/kernel/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