um: time: fix initialization in time-travel mode

In time-travel mode, since my previous patch, the start time was
initialized too late, so that the system would read it before we
set it, thus always starting system time at 0 (1970-01-01). This
happens because timekeeping_init() reads the time and is called
before time_init().

Unfortunately, I didn't see this before because I was testing it
only with the RTC patch applied (and enabled), and then the time
is read again by the RTC a little - after time_init() this time.

Fix this by just doing the initialization whenever necessary.

Fixes: 2701c1bd ("um: time: Fix read_persistent_clock64() in time-travel")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/kernel/time.c

@@ -535,6 +535,31 @@ static int time_travel_connect_external(const char *socket)
 
 	return 1;
 }
+
+static void time_travel_set_start(void)
+{
+	if (time_travel_start_set)
+		return;
+
+	switch (time_travel_mode) {
+	case TT_MODE_EXTERNAL:
+		time_travel_start = time_travel_ext_req(UM_TIMETRAVEL_GET_TOD, -1);
+		/* controller gave us the *current* time, so adjust by that */
+		time_travel_ext_get_time();
+		time_travel_start -= time_travel_time;
+		break;
+	case TT_MODE_INFCPU:
+	case TT_MODE_BASIC:
+		if (!time_travel_start_set)
+			time_travel_start = os_persistent_clock_emulation();
+		break;
+	case TT_MODE_OFF:
+		/* we just read the host clock with os_persistent_clock_emulation() */
+		break;
+	}
+
+	time_travel_start_set = true;
+}
 #else /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
 #define time_travel_start_set 0
 #define time_travel_start 0
@@ -553,6 +578,10 @@ static void time_travel_set_interval(unsigned long long interval)
 {
 }
 
+static inline void time_travel_set_start(void)
+{
+}
+
 /* fail link if this actually gets used */
 extern u64 time_travel_ext_req(u32 op, u64 time);
 
@@ -731,6 +760,8 @@ void read_persistent_clock64(struct timespec64 *ts)
 {
 	long long nsecs;
 
+	time_travel_set_start();
+
 	if (time_travel_mode != TT_MODE_OFF)
 		nsecs = time_travel_start + time_travel_time;
 	else
@@ -742,25 +773,6 @@ void read_persistent_clock64(struct timespec64 *ts)
 
 void __init time_init(void)
 {
-#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
-	switch (time_travel_mode) {
-	case TT_MODE_EXTERNAL:
-		time_travel_start = time_travel_ext_req(UM_TIMETRAVEL_GET_TOD, -1);
-		/* controller gave us the *current* time, so adjust by that */
-		time_travel_ext_get_time();
-		time_travel_start -= time_travel_time;
-		break;
-	case TT_MODE_INFCPU:
-	case TT_MODE_BASIC:
-		if (!time_travel_start_set)
-			time_travel_start = os_persistent_clock_emulation();
-		break;
-	case TT_MODE_OFF:
-		/* we just read the host clock with os_persistent_clock_emulation() */
-		break;
-	}
-#endif
-
 	timer_set_signal_handler();
 	late_time_init = um_timer_setup;
 }