Comment 1 for bug 1946220

When testing this manually with 4.15.0-159 on node appleton-kernel, I can see this hang issue after step 15.

Test output:
ubuntu@appleton-kernel:~/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests$ sudo make run_tests TARGETS=ftrace
make[1]: Entering directory '/home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/ftrace'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/ftrace'
make[1]: Entering directory '/home/ubuntu/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/ftrace'
TAP version 13
selftests: ftracetest
========================================
=== Ftrace unit tests ===
[1] Basic trace file check [PASS]
[2] Basic test for tracers [PASS]
[3] Basic trace clock test [PASS]
[4] Basic event tracing check [PASS]
[5] Snapshot and tracing setting [PASS]
[6] event tracing - enable/disable with event level files [PASS]
[7] event tracing - restricts events based on pid [PASS]
[8] event tracing - enable/disable with subsystem level files [PASS]
[9] event tracing - enable/disable with top level files [PASS]
[10] ftrace - function graph filters with stack tracer [PASS]
[11] ftrace - function graph filters [PASS]
[12] ftrace - function pid filters [PASS]
[13] ftrace - test for function event triggers [PASS]
[14] ftrace - function profiler with function tracing [PASS]
[15] ftrace - test reading of set_ftrace_filter [PASS]
[16] ftrace - test for function traceon/off triggers
(stopped here)

syslog output:
Oct 7 10:09:50 appleton-kernel systemd[1]: Started Session 4 of user ubuntu.
Oct 7 10:10:09 appleton-kernel kernel: [ 219.291897] Scheduler tracepoints stat_sleep, stat_iowait, stat_blocked and stat_runtime require the kernel parameter schedstats=enable or kernel.sched_schedstats=1
(stopped here)

dmesg output:
[ 219.291897] Scheduler tracepoints stat_sleep, stat_iowait, stat_blocked and stat_runtime require the kernel parameter schedstats=enable or kernel.sched_schedstats=1
[ 280.782083] Unable to handle kernel read from unreadable memory at virtual address 00000050
[ 280.790429] Mem abort info:
[ 280.793211] ESR = 0x96000004
[ 280.796287] Exception class = DABT (current EL), IL = 32 bits
[ 280.802225] SET = 0, FnV = 0
[ 280.805274] EA = 0, S1PTW = 0
[ 280.808421] Data abort info:
[ 280.811308] ISV = 0, ISS = 0x00000004
[ 280.815149] CM = 0, WnR = 0
[ 280.818123] user pgtable: 4k pages, 48-bit VAs, pgd = 0000000075661ca7
[ 280.824658] [0000000000000050] *pgd=0000000000000000
[ 280.829628] Internal error: Oops: 96000004 [#1] SMP
(stopped here)