posix: improve error out for mlockall() and pthread_create

- add strerror
 - mlockall skipped in lockstep builds (ENABLE_LOCKSTEP_SCHEDULER)

platforms/posix/src/px4/common/main.cpp

@@ -178,13 +178,13 @@ int main(int argc, char **argv)
 		return client.process_args(argc, (const char **)argv);
 
 	} else {
-#if (_POSIX_MEMLOCK > 0)
+#if (_POSIX_MEMLOCK > 0) && !defined(ENABLE_LOCKSTEP_SCHEDULER)
 
 		// try to lock address space into RAM, to avoid page swap delay
 		// TODO: Check CAP_IPC_LOCK instead of euid
 		if (geteuid() == 0) {   // root user
-			if (mlockall(MCL_CURRENT) + mlockall(MCL_FUTURE)) {	// check if both works
-				PX4_ERR("mlockall() failed! errno: %d", errno);
+			if (mlockall(MCL_CURRENT | MCL_FUTURE)) {	// check if both works
+				PX4_ERR("mlockall() failed! errno: %d (%s)", errno, strerror(errno));
 				munlockall();	// avoid mlock limitation caused alloc failure in future
 
 			} else {
@@ -192,7 +192,7 @@ int main(int argc, char **argv)
 			}
 		}
 
-#endif
+#endif // (_POSIX_MEMLOCK > 0) && !ENABLE_LOCKSTEP_SCHEDULER
 
 		/* Server/daemon apps need to parse the command line arguments. */
 

platforms/posix/src/px4/common/tasks.cpp

@@ -252,7 +252,7 @@ px4_task_t px4_task_spawn_cmd(const char *name, int scheduler, int priority, int
 			rv = pthread_create(&taskmap[taskid].pid, nullptr, &entry_adapter, (void *) taskdata);
 
 			if (rv != 0) {
-				PX4_ERR("px4_task_spawn_cmd: failed to create thread %d %d\n", rv, errno);
+				PX4_ERR("px4_task_spawn_cmd: failed to create thread for %s (%i): %s", name, rv, strerror(rv));
 				taskmap[taskid].isused = false;
 				pthread_attr_destroy(&attr);
 				pthread_mutex_unlock(&task_mutex);