Fix race condition in transaction timeout TAP tests

The interruption handler within the injection point can get stuck in an
infinite loop while handling transaction timeout. To avoid this situation
we reset the timeout flag before invoking the injection point.

Author: Alexander Korotkov
Reviewed-by: Andrey Borodin
Discussion: https://postgr.es/m/ZfPchPC6oNN71X2J%40paquier.xyz

Author: akorotkov

src/backend/tcop/postgres.c

@@ -3409,45 +3409,43 @@ ProcessInterrupts(void)
 		/*
 		 * If the GUC has been reset to zero, ignore the signal.  This is
 		 * important because the GUC update itself won't disable any pending
-		 * interrupt.
+		 * interrupt.  We need to unset the flag before the injection point,
+		 * otherwise we could loop in interrupts checking.
 		 */
+		IdleInTransactionSessionTimeoutPending = false;
 		if (IdleInTransactionSessionTimeout > 0)
 		{
 			INJECTION_POINT("idle-in-transaction-session-timeout");
 			ereport(FATAL,
 					(errcode(ERRCODE_IDLE_IN_TRANSACTION_SESSION_TIMEOUT),
 					 errmsg("terminating connection due to idle-in-transaction timeout")));
 		}
-		else
-			IdleInTransactionSessionTimeoutPending = false;
 	}
 
 	if (TransactionTimeoutPending)
 	{
 		/* As above, ignore the signal if the GUC has been reset to zero. */
+		TransactionTimeoutPending = false;
 		if (TransactionTimeout > 0)
 		{
 			INJECTION_POINT("transaction-timeout");
 			ereport(FATAL,
 					(errcode(ERRCODE_TRANSACTION_TIMEOUT),
 					 errmsg("terminating connection due to transaction timeout")));
 		}
-		else
-			TransactionTimeoutPending = false;
 	}
 
 	if (IdleSessionTimeoutPending)
 	{
 		/* As above, ignore the signal if the GUC has been reset to zero. */
+		IdleSessionTimeoutPending = false;
 		if (IdleSessionTimeout > 0)
 		{
 			INJECTION_POINT("idle-session-timeout");
 			ereport(FATAL,
 					(errcode(ERRCODE_IDLE_SESSION_TIMEOUT),
 					 errmsg("terminating connection due to idle-session timeout")));
 		}
-		else
-			IdleSessionTimeoutPending = false;
 	}
 
 	/*