selftests/tracing: Fix event filter test to retry up to 10 times

Commit eb50d0f250e9 ("selftests/ftrace: Choose target function for filter
test from samples") choose the target function from samples, but sometimes
this test failes randomly because the target function does not hit at the
next time. So retry getting samples up to 10 times.

Fixes: eb50d0f250e9 ("selftests/ftrace: Choose target function for filter test from samples")
Signed-off-by: Masami Hiramatsu (Google) <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/ftrace/test.d/filter/event-filter-function.tc

···
 }
 
 sample_events() {
-    echo > trace
     echo 1 > events/kmem/kmem_cache_free/enable
     echo 1 > tracing_on
     ls > /dev/null
···
 echo 0 > events/enable
 
 echo "Get the most frequently calling function"
+echo > trace
 sample_events
 
 target_func=`cat trace | grep -o 'call_site=\([^+]*\)' | sed 's/call_site=//' | sort | uniq -c | sort | tail -n 1 | sed 's/^[ 0-9]*//'`
···
 
 echo "Test event filter function name"
 echo "call_site.function == $target_func" > events/kmem/kmem_cache_free/filter
+
 sample_events
+max_retry=10
+while [ `grep kmem_cache_free trace| wc -l` -eq 0 ]; do
+sample_events
+max_retry=$((max_retry - 1))
+if [ $max_retry -eq 0 ]; then
+	exit_fail
+fi
+done
 
 hitcnt=`grep kmem_cache_free trace| grep $target_func | wc -l`
 misscnt=`grep kmem_cache_free trace| grep -v $target_func | wc -l`
···
 
 echo "Test event filter function address"
 echo "call_site.function == 0x$address" > events/kmem/kmem_cache_free/filter
+echo > trace
 sample_events
+max_retry=10
+while [ `grep kmem_cache_free trace| wc -l` -eq 0 ]; do
+sample_events
+max_retry=$((max_retry - 1))
+if [ $max_retry -eq 0 ]; then
+	exit_fail
+fi
+done
 
 hitcnt=`grep kmem_cache_free trace| grep $target_func | wc -l`
 misscnt=`grep kmem_cache_free trace| grep -v $target_func | wc -l`