ftrace test in ubuntu_kernel_selftest failed on X/B/C s390x KVM

4 tests failed:
[11] ftrace - function glob filters [FAIL]
[23] Kprobe event argument syntax [FAIL]
[36] event trigger - test histogram trigger [FAIL]
[51] (instance) event trigger - test histogram trigger [FAIL]

With the test suite in the upstream kernel tree, 3 of these failures can be reproduced, except this one:
-e -n [34] Kprobe event argument syntax
-e [UNTESTED]

$ sudo make -C linux/tools/testing/selftests TARGETS=ftrace run_tests
make: Entering directory '/home/ubuntu/src/linux/tools/testing/selftests'
make[1]: Entering directory '/home/ubuntu/src/linux/tools/testing/selftests/ftrace'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/ubuntu/src/linux/tools/testing/selftests/ftrace'
make[1]: Entering directory '/home/ubuntu/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] event tracing - enable/disable with event level files [PASS]
[6] event tracing - restricts events based on pid [PASS]
[7] event tracing - enable/disable with subsystem level files [PASS]
[8] event tracing - enable/disable with top level files [PASS]
[9] ftrace - function graph filters with stack tracer [PASS]
[10] ftrace - function graph filters [PASS]
[11] ftrace - function glob filters [FAIL]
[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 [PASS]
[17] Test creation and deletion of trace instances while setting an event [PASS]
[18] Test creation and deletion of trace instances [PASS]
[19] Kprobe dynamic event - adding and removing [PASS]
[20] Kprobe dynamic event - busy event check [PASS]
[21] Kprobe dynamic event with arguments [PASS]
[22] Kprobe event string type argument [UNTESTED]
[23] Kprobe event argument syntax [FAIL]
[24] Kprobes event arguments with types [PASS]
[25] Kprobe event auto/manual naming [PASS]
[26] Kprobe dynamic event with function tracer [PASS]
[27] Kprobe dynamic event - probing module [PASS]
[28] Kretprobe dynamic event with arguments [PASS]
[29] Kretprobe dynamic event with maxactive [PASS]
[30] Register/unregister many kprobe events [PASS]
[31] Kprobe events - probe points [PASS]
[32] event trigger - test multiple actions on hist trigger [UNSUPPORTED]
[33] event trigger - test event enable/disable trigger [PASS]
[34] event trigger - test trigger filter [PASS]
[35] event trigger - test histogram modifiers [PASS]
[36] event trigger - test histogram trigger [FAIL]
[37] event trigger - test multiple histogram triggers [PASS]
[38] event trigger - test snapshot-trigger [PASS]
[39] event trigger - test stacktrace-trigger [PASS]
[40] event trigger - test traceon/off trigger [PASS]
[41] (instance) Basic test for tracers [PASS]
[42] (instance) Basic trace clock test [PASS]
[43] (instance) event tracing - enable/disable with event level files [PASS]
[44] (instance) event tracing - restricts events based on pid [PASS]
[45] (instance) event tracing - enable/disable with subsystem level files [PASS]
[46] (instance) ftrace - test for function event triggers [PASS]
[47] (instance) ftrace - test for function traceon/off triggers [PASS]
[48] (instance) event trigger - test event enable/disable trigger [PASS]
[49] (instance) event trigger - test trigger filter [PASS]
[50] (instance) event trigger - test histogram modifiers [PASS]
[51] (instance) event trigger - test histogram trigger [FAIL]
[52] (instance) event trigger - test multiple histogram triggers [PASS]

# of passed: 46
# of failed: 4
# of unresolved: 0
# of untested: 1
# of unsupported: 1
# of xfailed: 0
# of undefined(test bug): 0
not ok 1..1 selftests: ftracetest [FAIL]
make[1]: Leaving directory '/home/ubuntu/src/linux/tools/testing/selftests/ftrace'
make: Leaving directory '/home/ubuntu/src/linux/tools/testing/selftests'

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: linux-image-4.15.0-43-generic 4.15.0-43.46
ProcVersionSignature: Ubuntu 4.15.0-43.46-generic 4.15.18
Uname: Linux 4.15.0-43-generic s390x
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access '/dev/snd/': No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay': 'aplay'
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: s390x
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord': 'arecord'
CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
Date: Mon Dec 24 06:46:11 2018
HibernationDevice: RESUME=UUID=caaee9b2-6bc1-4c8e-b26c-69038c092091
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig': 'iwconfig'
Lspci:

Lsusb: Error: command ['lsusb'] failed with exit code 1:
PciMultimedia:

ProcFB: Error: [Errno 2] No such file or directory: '/proc/fb'
ProcKernelCmdLine: root=UUID=c7d7bbcb-a039-4ead-abfe-7672dea0add4 crashkernel=196M
RelatedPackageVersions:
 linux-restricted-modules-4.15.0-43-generic N/A
 linux-backports-modules-4.15.0-43-generic N/A
 linux-firmware 1.173.3
RfKill: Error: [Errno 2] No such file or directory: 'rfkill': 'rfkill'
SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)