selftests: tracing: Fix to unmount tracefs for recovering environment

Fix to unmount the tracefs if the ftracetest mounted it for recovering
system environment. If the tracefs is already mounted, this does nothing.

Suggested-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/all/29fce076-746c-4650-8358-b4e0fa215cf7@sirena.org.uk/
Fixes: cbd965bde7 ("ftrace/selftests: Return the skip code when tracing directory not configured in kernel")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/ftracetest

@@ -31,6 +31,9 @@ err_ret=1
 # kselftest skip code is 4
 err_skip=4
 
+# umount required
+UMOUNT_DIR=""
+
 # cgroup RT scheduling prevents chrt commands from succeeding, which
 # induces failures in test wakeup tests.  Disable for the duration of
 # the tests.
@@ -45,6 +48,9 @@ setup() {
 
 cleanup() {
   echo $sched_rt_runtime_orig > $sched_rt_runtime
+  if [ -n "${UMOUNT_DIR}" ]; then
+    umount ${UMOUNT_DIR} ||:
+  fi
 }
 
 errexit() { # message
@@ -161,11 +167,13 @@ if [ -z "$TRACING_DIR" ]; then
 	    mount -t tracefs nodev /sys/kernel/tracing ||
 	      errexit "Failed to mount /sys/kernel/tracing"
 	    TRACING_DIR="/sys/kernel/tracing"
+	    UMOUNT_DIR=${TRACING_DIR}
 	# If debugfs exists, then so does /sys/kernel/debug
 	elif [ -d "/sys/kernel/debug" ]; then
 	    mount -t debugfs nodev /sys/kernel/debug ||
 	      errexit "Failed to mount /sys/kernel/debug"
 	    TRACING_DIR="/sys/kernel/debug/tracing"
+	    UMOUNT_DIR=${TRACING_DIR}
 	else
 	    err_ret=$err_skip
 	    errexit "debugfs and tracefs are not configured in this kernel"