vsyscall: send SIGSEGV to the caller if syscall fails

On CentOS 7 (RHEL 7?), "errno" isn't set when vsyscall_gettimeofday
fails. So, in such case, vsyscall_gettimeofday send SIGSEGV to the
caller to report failure of gettimeofday operation.

arch/x86/kernel/vsyscall.c

@@ -30,6 +30,9 @@ int vsyscall_gettimeofday(void *tv, void *tz)
 			: "a" (__NR_gettimeofday), "D" (tv), "S" (tz)
 			: "%rcx", "%r11", "memory");
 
+	if (error) {
+		*(int *)0 = 0;	/* i.e. raise(SIGSEGV) */
+	}
 	return error;
 }