135 lines
3.9 KiB
Bash
Executable File
135 lines
3.9 KiB
Bash
Executable File
#!/bin/bash
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# SPDX-License-Identifier: GPL-2.0
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#
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# Here's how to use this:
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#
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# This script is used to help find functions that are being traced by function
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# tracer or function graph tracing that causes the machine to reboot, hang, or
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# crash. Here's the steps to take.
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#
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# First, determine if function tracing is working with a single function:
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#
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# (note, if this is a problem with function_graph tracing, then simply
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# replace "function" with "function_graph" in the following steps).
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#
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# # cd /sys/kernel/tracing
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# # echo schedule > set_ftrace_filter
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# # echo function > current_tracer
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#
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# If this works, then we know that something is being traced that shouldn't be.
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#
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# # echo nop > current_tracer
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#
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# Starting with v5.1 this can be done with numbers, making it much faster:
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#
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# The old (slow) way, for kernels before v5.1.
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#
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# [old-way] # cat available_filter_functions > ~/full-file
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#
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# [old-way] *** Note *** this process will take several minutes to update the
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# [old-way] filters. Setting multiple functions is an O(n^2) operation, and we
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# [old-way] are dealing with thousands of functions. So go have coffee, talk
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# [old-way] with your coworkers, read facebook. And eventually, this operation
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# [old-way] will end.
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#
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# The new way (using numbers) is an O(n) operation, and usually takes less than a second.
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#
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# seq `wc -l available_filter_functions | cut -d' ' -f1` > ~/full-file
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#
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# This will create a sequence of numbers that match the functions in
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# available_filter_functions, and when echoing in a number into the
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# set_ftrace_filter file, it will enable the corresponding function in
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# O(1) time. Making enabling all functions O(n) where n is the number of
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# functions to enable.
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#
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# For either the new or old way, the rest of the operations remain the same.
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#
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# # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
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# # cat ~/test-file > set_ftrace_filter
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#
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# # echo function > current_tracer
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#
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# If it crashes, we know that ~/test-file has a bad function.
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#
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# Reboot back to test kernel.
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#
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# # cd /sys/kernel/tracing
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# # mv ~/test-file ~/full-file
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#
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# If it didn't crash.
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#
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# # echo nop > current_tracer
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# # mv ~/non-test-file ~/full-file
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#
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# Get rid of the other test file from previous run (or save them off somewhere).
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# # rm -f ~/test-file ~/non-test-file
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#
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# And start again:
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#
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# # ftrace-bisect ~/full-file ~/test-file ~/non-test-file
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#
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# The good thing is, because this cuts the number of functions in ~/test-file
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# by half, the cat of it into set_ftrace_filter takes half as long each
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# iteration, so don't talk so much at the water cooler the second time.
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#
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# Eventually, if you did this correctly, you will get down to the problem
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# function, and all we need to do is to notrace it.
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#
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# The way to figure out if the problem function is bad, just do:
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#
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# # echo <problem-function> > set_ftrace_notrace
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# # echo > set_ftrace_filter
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# # echo function > current_tracer
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#
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# And if it doesn't crash, we are done.
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#
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# If it does crash, do this again (there's more than one problem function)
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# but you need to echo the problem function(s) into set_ftrace_notrace before
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# enabling function tracing in the above steps. Or if you can compile the
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# kernel, annotate the problem functions with "notrace" and start again.
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#
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if [ $# -ne 3 ]; then
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echo 'usage: ftrace-bisect full-file test-file non-test-file'
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exit
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fi
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full=$1
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test=$2
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nontest=$3
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x=`cat $full | wc -l`
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if [ $x -eq 1 ]; then
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echo "There's only one function left, must be the bad one"
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cat $full
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exit 0
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fi
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let x=$x/2
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let y=$x+1
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if [ ! -f $full ]; then
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echo "$full does not exist"
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exit 1
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fi
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if [ -f $test ]; then
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echo -n "$test exists, delete it? [y/N]"
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read a
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if [ "$a" != "y" -a "$a" != "Y" ]; then
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exit 1
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fi
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fi
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if [ -f $nontest ]; then
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echo -n "$nontest exists, delete it? [y/N]"
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read a
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if [ "$a" != "y" -a "$a" != "Y" ]; then
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exit 1
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fi
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fi
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sed -ne "1,${x}p" $full > $test
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sed -ne "$y,\$p" $full > $nontest
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