ubuntu_kernel_selftests.ftrace:ftracetest fails with bionic:linux 4.15.0-168.176 on s390x

SRU Justification

[Impact]

There seems to have been a typo in Commit 85bf17b28f97
("recordmcount.pl: look for jgnop instruction as well as bcrl on s390")
that causes errors in finding mcount locations. This seems to cause problems with ftrace initialization leading to not being able to use ftrace
functions.

[Fix]

Fix the typo by changing it to the correct instruction.

[Test Case]

Ftrace files in /sys/kernel/debug/tracing should be able to be read from and written to with normal functionality. Ftrace selftests should now pass.

[Where things could go wrong]

Its a simple typo fix so none really.

-------------------------------------------------------
All ftrace tests from selftests are failing with bionic:linux 4.15.0-168.176 on s390x:

https://autopkgtest.ubuntu.com/results/autopkgtest-bionic/bionic/s390x/l/linux/20220201_190955_5689e@/log.gz

==========================================================================
selftests: ftracetest
========================================
=== Ftrace unit tests ===
[1] Basic trace file check [FAIL]
[2] Basic test for tracers [FAIL]
[3] Basic trace clock test [FAIL]
[4] Basic event tracing check [FAIL]
[5] Snapshot and tracing setting [FAIL]
[6] event tracing - enable/disable with event level files [FAIL]
[7] event tracing - restricts events based on pid [FAIL]
[8] event tracing - enable/disable with subsystem level files [FAIL]
[9] event tracing - enable/disable with top level files [FAIL]
[10] ftrace - function graph filters with stack tracer [FAIL]
[11] ftrace - function graph filters [FAIL]
[12] ftrace - function pid filters [FAIL]
[13] ftrace - test for function event triggers [FAIL]
[14] ftrace - function profiler with function tracing [FAIL]
[15] ftrace - test reading of set_ftrace_filter [FAIL]
[16] ftrace - test for function traceon/off triggers [FAIL]
[17] Test creation and deletion of trace instances while setting an event [FAIL]
[18] Test creation and deletion of trace instances [FAIL]
[19] Kprobe dynamic event - adding and removing [FAIL]
[20] Kprobe dynamic event - busy event check [FAIL]
[21] Kprobe dynamic event with arguments [FAIL]
[22] Kprobe event string type argument [FAIL]
[23] Kprobe event argument syntax [FAIL]
[24] Kprobes event arguments with types [FAIL]
[25] Kprobe event auto/manual naming [FAIL]
[26] Kprobe dynamic event with function tracer [FAIL]
[27] Kretprobe dynamic event with arguments [FAIL]
[28] Kretprobe dynamic event with maxactive [FAIL]
[29] Register/unregister many kprobe events [FAIL]
[30] event trigger - test multiple actions on hist trigger [FAIL]
[31] event trigger - test synthetic_events syntax parser [FAIL]
[32] event trigger - test event enable/disable trigger [FAIL]
[33] event trigger - test trigger filter [FAIL]
[34] event trigger - test histogram modifiers [FAIL]
[35] event trigger - test multiple histogram triggers [FAIL]
[36] event trigger - test snapshot-trigger [FAIL]
[37] event trigger - test stacktrace-trigger [FAIL]
[38] event trigger - test traceon/off trigger [FAIL]
[39] (instance) Basic test for tracers [FAIL]
[40] (instance) Basic trace clock test [FAIL]
[41] (instance) Snapshot and tracing setting [FAIL]
[42] (instance) event tracing - enable/disable with event level files [FAIL]
[43] (instance) event tracing - restricts events based on pid [FAIL]
[44] (instance) event tracing - enable/disable with subsystem level files [FAIL]
[45] (instance) ftrace - test for function event triggers [FAIL]
[46] (instance) ftrace - test for function traceon/off triggers [FAIL]
[47] (instance) event trigger - test event enable/disable trigger [FAIL]
[48] (instance) event trigger - test trigger filter [FAIL]
[49] (instance) event trigger - test histogram modifiers [FAIL]
[50] (instance) event trigger - test multiple histogram triggers [FAIL]

# of passed: 0
# of failed: 50
# of unresolved: 0
# of untested: 0
# of unsupported: 0
# of xfailed: 0
# of undefined(test bug): 0
not ok 1..1 selftests: ftracetest [FAIL]
==========================================================================

After some debugging I've found out that the testcases are not actually run, the failure happens while running 'tools/testing/selftests/ftrace/test.d/functions:initialize_ftrace()', on the following line:

[ -f set_ftrace_filter ] && echo | tee set_ftrace_*

After a reboot for clean ftrace state, with kernel 4.15.0-168-generic:

root@kleber-bionic:/sys/kernel/debug/tracing# head set_ftrace_*
head: cannot open 'set_ftrace_filter' for reading: No such device
head: cannot open 'set_ftrace_notrace' for reading: No such device
==> set_ftrace_pid <==
no pid

With kernel 4.15.0-167-generic:

root@kleber-bionic-2:/sys/kernel/debug/tracing# head set_ftrace_*
==> set_ftrace_filter <==
#### all functions enabled ####

==> set_ftrace_notrace <==
#### no functions disabled ####

==> set_ftrace_pid <==
no pid