lkl: Warn if lkl_create_syscall_thread seems unproperly used

arch/lkl/include/uapi/asm/host_ops.h

@@ -23,6 +23,7 @@ struct lkl_sem_t;
  * @sem_free - free a host semaphore
  * @sem_up - perform an up operation on the semaphore
  * @sem_down - perform a down operation on the semaphore
+ * @sem_get - return the current value of semahpore. To be used only for sanity checking
  *
  * @mutex_alloc - allocate and initialize a host mutex
  * @mutex_free - free a host mutex
@@ -66,6 +67,7 @@ struct lkl_host_operations {
 	void (*sem_free)(struct lkl_sem_t *sem);
 	void (*sem_up)(struct lkl_sem_t *sem);
 	void (*sem_down)(struct lkl_sem_t *sem);
+	int (*sem_get)(struct lkl_sem_t *sem);
 
 	struct lkl_mutex_t *(*mutex_alloc)(void);
 	void (*mutex_free)(struct lkl_mutex_t *mutex);

arch/lkl/kernel/syscalls.c

@@ -147,16 +147,31 @@ static int syscall_thread_data_init(struct syscall_thread_data *data,
 	return 0;
 }
 
-long lkl_syscall(long no, long *params)
-{
+static struct syscall_thread_data *lkl_syscall_data(void) {
 	struct syscall_thread_data *data = NULL;
-	struct syscall s;
 
 	if (lkl_ops->tls_get)
 		data = lkl_ops->tls_get(syscall_thread_data_key);
 	if (!data)
 		data = &default_syscall_thread_data;
 
+	return data;
+}
+
+static int lkl_syscall_wouldblock(void) {
+	struct syscall_thread_data *data = lkl_syscall_data();
+
+	if(!lkl_ops->sem_get)
+		return 0;
+
+	return !lkl_ops->sem_get(data->mutex);
+}
+
+long lkl_syscall(long no, long *params)
+{
+	struct syscall_thread_data *data = lkl_syscall_data();
+	struct syscall s;
+
 	s.no = no;
 	s.params = params;
 
@@ -196,6 +211,9 @@ int lkl_create_syscall_thread(void)
 		return ret;
 	}
 
+	if(lkl_syscall_wouldblock())
+		pr_warn("lkl: Calling lkl_create_syscall_thread will block\n");
+
 	params[0] = (long)data;
 	ret = lkl_syscall(__NR_create_syscall_thread, params);
 	if (ret < 0) {

tools/lkl/lib/posix-host.c

@@ -123,6 +123,17 @@ static void sem_down(struct lkl_sem_t *sem)
 #endif /* _POSIX_SEMAPHORES */
 }
 
+static int sem_get(struct lkl_sem_t *sem) {
+	int v = 0;
+#ifdef _POSIX_SEMAPHORES
+	WARN_UNLESS(sem_getvalue(&sem->sem, &v));
+#else
+	WARN_PTHREAD(pthread_mutex_lock(&sem->lock));
+	v = sem->count;
+	WARN_PTHREAD(pthread_mutex_unlock(&sem->lock));
+#endif /* _POSIX_SEMAPHORES */
+	return v;
+}
 
 static struct lkl_mutex_t *mutex_alloc(void)
 {
@@ -268,6 +279,7 @@ struct lkl_host_operations lkl_host_ops = {
 	.sem_free = sem_free,
 	.sem_up = sem_up,
 	.sem_down = sem_down,
+	.sem_get = sem_get,
 	.mutex_alloc = mutex_alloc,
 	.mutex_free = mutex_free,
 	.mutex_lock = mutex_lock,