Avoid assuming that time_t can fit in an int.

We had several places that used cast-to-unsigned-int as a substitute
for properly checking for overflow.  Coverity has started objecting
to that practice as likely introducing Y2038 bugs.  An extra
comparison is surely not much compared to the cost of time(NULL), nor
is this coding practice particularly readable.  Let's do it honestly,
with explicit logic covering the cases of first-time-through and
clock-went-backwards.

I don't feel a need to back-patch though: our released versions
will be out of support long before 2038, and besides which I think
the code would accidentally work anyway for another 70 years or so.

src/backend/postmaster/pgarch.c

@@ -185,8 +185,8 @@ PgArchShmemInit(void)
 /*
  * PgArchCanRestart
  *
- * Return true and archiver is allowed to restart if enough time has
- * passed since it was launched last to reach PGARCH_RESTART_INTERVAL.
+ * Return true, indicating archiver is allowed to restart, if enough time has
+ * passed since it was last launched to reach PGARCH_RESTART_INTERVAL.
  * Otherwise return false.
  *
  * This is a safety valve to protect against continuous respawn attempts if the
@@ -201,15 +201,18 @@ PgArchCanRestart(void)
 	time_t		curtime = time(NULL);
 
 	/*
-	 * Return false and don't restart archiver if too soon since last archiver
-	 * start.
+	 * If first time through, or time somehow went backwards, always update
+	 * last_pgarch_start_time to match the current clock and allow archiver
+	 * start.  Otherwise allow it only once enough time has elapsed.
 	 */
-	if ((unsigned int) (curtime - last_pgarch_start_time) <
-		(unsigned int) PGARCH_RESTART_INTERVAL)
-		return false;
-
-	last_pgarch_start_time = curtime;
-	return true;
+	if (last_pgarch_start_time == 0 ||
+		curtime < last_pgarch_start_time ||
+		curtime - last_pgarch_start_time >= PGARCH_RESTART_INTERVAL)
+	{
+		last_pgarch_start_time = curtime;
+		return true;
+	}
+	return false;
 }
 
 
@@ -332,7 +335,8 @@ pgarch_MainLoop(void)
 		 * SIGUSR2 arrives.  However, that means a random SIGTERM would
 		 * disable archiving indefinitely, which doesn't seem like a good
 		 * idea.  If more than 60 seconds pass since SIGTERM, exit anyway, so
-		 * that the postmaster can start a new archiver if needed.
+		 * that the postmaster can start a new archiver if needed.  Also exit
+		 * if time unexpectedly goes backward.
 		 */
 		if (ShutdownRequestPending)
 		{
@@ -340,8 +344,8 @@ pgarch_MainLoop(void)
 
 			if (last_sigterm_time == 0)
 				last_sigterm_time = curtime;
-			else if ((unsigned int) (curtime - last_sigterm_time) >=
-					 (unsigned int) 60)
+			else if (curtime < last_sigterm_time ||
+					 curtime - last_sigterm_time >= 60)
 				break;
 		}
 

src/backend/postmaster/postmaster.c

@@ -1557,13 +1557,21 @@ DetermineSleepTime(void)
 	{
 		if (AbortStartTime != 0)
 		{
+			time_t		curtime = time(NULL);
 			int			seconds;
 
-			/* time left to abort; clamp to 0 in case it already expired */
-			seconds = SIGKILL_CHILDREN_AFTER_SECS -
-				(time(NULL) - AbortStartTime);
+			/*
+			 * time left to abort; clamp to 0 if it already expired, or if
+			 * time goes backwards
+			 */
+			if (curtime < AbortStartTime ||
+				curtime - AbortStartTime >= SIGKILL_CHILDREN_AFTER_SECS)
+				seconds = 0;
+			else
+				seconds = SIGKILL_CHILDREN_AFTER_SECS -
+					(curtime - AbortStartTime);
 
-			return Max(seconds * 1000, 0);
+			return seconds * 1000;
 		}
 		else
 			return 60 * 1000;

src/backend/replication/logical/slotsync.c

@@ -1636,8 +1636,9 @@ ShutDownSlotSync(void)
 /*
  * SlotSyncWorkerCanRestart
  *
- * Returns true if enough time (SLOTSYNC_RESTART_INTERVAL_SEC) has passed
- * since it was launched last. Otherwise returns false.
+ * Return true, indicating worker is allowed to restart, if enough time has
+ * passed since it was last launched to reach SLOTSYNC_RESTART_INTERVAL_SEC.
+ * Otherwise return false.
  *
  * This is a safety valve to protect against continuous respawn attempts if the
  * worker is dying immediately at launch. Note that since we will retry to
@@ -1649,14 +1650,19 @@ SlotSyncWorkerCanRestart(void)
 {
 	time_t		curtime = time(NULL);
 
-	/* Return false if too soon since last start. */
-	if ((unsigned int) (curtime - SlotSyncCtx->last_start_time) <
-		(unsigned int) SLOTSYNC_RESTART_INTERVAL_SEC)
-		return false;
-
-	SlotSyncCtx->last_start_time = curtime;
-
-	return true;
+	/*
+	 * If first time through, or time somehow went backwards, always update
+	 * last_start_time to match the current clock and allow worker start.
+	 * Otherwise allow it only once enough time has elapsed.
+	 */
+	if (SlotSyncCtx->last_start_time == 0 ||
+		curtime < SlotSyncCtx->last_start_time ||
+		curtime - SlotSyncCtx->last_start_time >= SLOTSYNC_RESTART_INTERVAL_SEC)
+	{
+		SlotSyncCtx->last_start_time = curtime;
+		return true;
+	}
+	return false;
 }
 
 /*