selftests/ftrace: Improve kprobe on module testcase to load/unload module

Improve kprobe events on module testcase to check module
load/unload with disabled/enabled events. This also change
the target module to trace_printk.ko, so it depends on
CONFIG_SAMPLE_TRACE_PRINTK=m.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>

tools/testing/selftests/ftrace/config

@@ -7,3 +7,7 @@ CONFIG_HIST_TRIGGERS=y
 CONFIG_PREEMPT_TRACER=y
 CONFIG_IRQSOFF_TRACER=y
 CONFIG_PREEMPTIRQ_DELAY_TEST=m
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+CONFIG_SAMPLES=y
+CONFIG_SAMPLE_TRACE_PRINTK=m

tools/testing/selftests/ftrace/test.d/kprobe/kprobe_module.tc

@@ -4,11 +4,18 @@
 
 [ -f kprobe_events ] || exit_unsupported # this is configurable
 
+rmmod trace-printk ||:
+if ! modprobe trace-printk ; then
+  echo "No trace-printk sample module - please make CONFIG_SAMPLE_TRACE_PRINTK=
+m"
+  exit_unresolved;
+fi
+
+MOD=trace_printk
+FUNC=trace_printk_irq_work
+
 :;: "Add an event on a module function without specifying event name" ;:
 
-MOD=`lsmod | head -n 2 | tail -n 1 | cut -f1 -d" "`
-FUNC=`grep -m 1 ".* t .*\\[$MOD\\]" /proc/kallsyms | xargs | cut -f3 -d" "`
-[ "x" != "x$MOD" -a "y" != "y$FUNC" ] || exit_unresolved
 echo "p $MOD:$FUNC" > kprobe_events
 PROBE_NAME=`echo $MOD:$FUNC | tr ".:" "_"`
 test -d events/kprobes/p_${PROBE_NAME}_0 || exit_failure
@@ -22,3 +29,25 @@ test -d events/kprobes/event1 || exit_failure
 
 echo "p:kprobes1/event1 $MOD:$FUNC" > kprobe_events
 test -d events/kprobes1/event1 || exit_failure
+
+:;: "Remove target module, but event still be there" ;:
+if ! rmmod trace-printk ; then
+  echo "Failed to unload module - please enable CONFIG_MODULE_UNLOAD"
+  exit_unresolved;
+fi
+test -d events/kprobes1/event1
+
+:;: "Check posibility to defining events on unloaded module";:
+echo "p:event2 $MOD:$FUNC" >> kprobe_events
+
+:;: "Target is gone, but we can prepare for next time";:
+echo 1 > events/kprobes1/event1/enable
+
+:;: "Load module again, which means the event1 should be recorded";:
+modprobe trace-printk
+grep "event1:" trace
+
+:;: "Remove the module again and check the event is not locked"
+rmmod trace-printk
+echo 0 > events/kprobes1/event1/enable
+echo "-:kprobes1/event1" >> kprobe_events