Index: uspace/lib/c/generic/fibril_synch.c
===================================================================
--- uspace/lib/c/generic/fibril_synch.c	(revision be942bcc856b2dbd86ad3891336fb7b52bb2b624)
+++ uspace/lib/c/generic/fibril_synch.c	(revision b0a76d5b0890440e8cc9c28afd0d4bd417bb5546)
@@ -139,5 +139,4 @@
 static void _fibril_mutex_unlock_unsafe(fibril_mutex_t *fm)
 {
-	assert(fm->counter <= 0);
 	if (fm->counter++ < 0) {
 		link_t *tmp;
@@ -165,7 +164,20 @@
 void fibril_mutex_unlock(fibril_mutex_t *fm)
 {
+	assert(fibril_mutex_is_locked(fm));
 	futex_down(&async_futex);
 	_fibril_mutex_unlock_unsafe(fm);
 	futex_up(&async_futex);
+}
+
+bool fibril_mutex_is_locked(fibril_mutex_t *fm)
+{
+	bool locked = false;
+	
+	futex_down(&async_futex);
+	if (fm->counter <= 0) 
+		locked = true;
+	futex_up(&async_futex);
+	
+	return locked;
 }
 
@@ -230,5 +242,4 @@
 {
 	futex_down(&async_futex);
-	assert(frw->readers || (frw->writers == 1));
 	if (frw->readers) {
 		if (--frw->readers) {
@@ -296,4 +307,5 @@
 void fibril_rwlock_read_unlock(fibril_rwlock_t *frw)
 {
+	assert(fibril_rwlock_is_read_locked(frw));
 	_fibril_rwlock_common_unlock(frw);
 }
@@ -301,5 +313,32 @@
 void fibril_rwlock_write_unlock(fibril_rwlock_t *frw)
 {
+	assert(fibril_rwlock_is_write_locked(frw));
 	_fibril_rwlock_common_unlock(frw);
+}
+
+bool fibril_rwlock_is_read_locked(fibril_rwlock_t *frw)
+{
+	bool locked = false;
+
+	futex_down(&async_futex);
+	if (frw->readers)
+		locked = true;
+	futex_up(&async_futex);
+
+	return locked;
+}
+
+bool fibril_rwlock_is_write_locked(fibril_rwlock_t *frw)
+{
+	bool locked = false;
+
+	futex_down(&async_futex);
+	if (frw->writers) {
+		assert(frw->writers == 1);
+		locked = true;
+	}
+	futex_up(&async_futex);
+
+	return locked;
 }
 
@@ -314,4 +353,6 @@
 {
 	awaiter_t wdata;
+
+	assert(fibril_mutex_is_locked(fm));
 
 	if (timeout < 0)
Index: uspace/lib/c/include/fibril_synch.h
===================================================================
--- uspace/lib/c/include/fibril_synch.h	(revision be942bcc856b2dbd86ad3891336fb7b52bb2b624)
+++ uspace/lib/c/include/fibril_synch.h	(revision b0a76d5b0890440e8cc9c28afd0d4bd417bb5546)
@@ -105,4 +105,5 @@
 extern bool fibril_mutex_trylock(fibril_mutex_t *);
 extern void fibril_mutex_unlock(fibril_mutex_t *);
+extern bool fibril_mutex_is_locked(fibril_mutex_t *);
 
 extern void fibril_rwlock_initialize(fibril_rwlock_t *);
@@ -111,4 +112,6 @@
 extern void fibril_rwlock_read_unlock(fibril_rwlock_t *);
 extern void fibril_rwlock_write_unlock(fibril_rwlock_t *);
+extern bool fibril_rwlock_is_read_locked(fibril_rwlock_t *);
+extern bool fibril_rwlock_is_write_locked(fibril_rwlock_t *);
 
 extern void fibril_condvar_initialize(fibril_condvar_t *);