diff --git a/acx_func.h b/acx_func.h
index a8e2482..239698b 100644
--- a/acx_func.h
+++ b/acx_func.h
@@ -307,27 +307,18 @@ acx_unlock_helper(acx_device_t *adev, un
 	acx_unlock_debug(adev, where);
 	spin_unlock_irqrestore(&adev->lock, *fp);
 }
-static inline void
-acx_down_helper(acx_device_t *adev, const char* where)
-{
-	acx_down_debug(adev, where);
-}
-static inline void
-acx_up_helper(acx_device_t *adev, const char* where)
-{
-	acx_up_debug(adev, where);
-}
+
 #define acx_lock(adev, flags)	acx_lock_helper(adev, &(flags), __FILE__ ":" STRING(__LINE__))
 #define acx_unlock(adev, flags)	acx_unlock_helper(adev, &(flags), __FILE__ ":" STRING(__LINE__))
-#define acx_sem_lock(adev)	acx_down_helper(adev, __FILE__ ":" STRING(__LINE__))
-#define acx_sem_unlock(adev)	acx_up_helper(adev, __FILE__ ":" STRING(__LINE__))
+#define acx_sem_lock(adev)	mutex_lock(&(adev)->mutex)
+#define acx_sem_unlock(adev)	mutex_unlock(&(adev)->mutex)
 
 #elif defined(DO_LOCKING)
 
 #define acx_lock(adev, flags)	spin_lock_irqsave(&adev->lock, flags)
 #define acx_unlock(adev, flags)	spin_unlock_irqrestore(&adev->lock, flags)
-#define acx_sem_lock(adev)	down(&adev->sem)
-#define acx_sem_unlock(adev)	up(&adev->sem)
+#define acx_sem_lock(adev)	mutex_lock(&(adev)->mutex)
+#define acx_sem_unlock(adev)	mutex_unlock(&(adev)->mutex)
 #define acx_lock_unhold()	((void)0)
 #define acx_sem_unhold()	((void)0)
 
diff --git a/acx_struct.h b/acx_struct.h
index 0bd18c4..65d6cf5 100644
--- a/acx_struct.h
+++ b/acx_struct.h
@@ -1142,7 +1142,7 @@ struct acx_device {
 	/* FIXME: try to convert semaphore to more efficient mutex according
 	   to Ingo Molnar's docs (but not before driver is in mainline or
 		 pre-mutex Linux 2.6.10 is very outdated). */
-	struct semaphore	sem;
+	struct mutex	mutex;
 	spinlock_t		lock;
 #if defined(PARANOID_LOCKING) /* Lock debugging */
 	const char		*last_sem;
diff --git a/common.c b/common.c
index 70e8afc..c019cef 100644
--- a/common.c
+++ b/common.c
@@ -189,59 +189,7 @@ acx_unlock_debug(acx_device_t *adev, con
 		}
 	}
 }
-void
-acx_down_debug(acx_device_t *adev, const char* where)
-{
-	int sem_count;
-	unsigned long timeout = jiffies + 5*HZ;
-
-	where = sanitize_str(where);
 
-	for (;;) {
-		sem_count = atomic_read(&adev->sem.count);
-		if (sem_count) break;
-		if (time_after(jiffies, timeout))
-			break;
-		msleep(5);
-	}
-	if (!sem_count) {
-		printk(KERN_EMERG "D STATE at %s! last sem at %s\n",
-			where, adev->last_sem);
-		dump_stack();
-	}
-	adev->last_sem = where;
-	adev->sem_time = jiffies;
-	down(&adev->sem);
-	if (acx_debug & L_LOCK) {
-		printk("%s: sem_down %d -> %d\n",
-			where, sem_count, atomic_read(&adev->sem.count));
-	}
-}
-void
-acx_up_debug(acx_device_t *adev, const char* where)
-{
-	int sem_count = atomic_read(&adev->sem.count);
-	if (sem_count) {
-		where = sanitize_str(where);
-		printk(KERN_EMERG "STRAY UP at %s! sem.count=%d\n", where, sem_count);
-		dump_stack();
-	}
-	if (acx_debug & L_LOCK) {
-		unsigned long diff = jiffies - adev->sem_time;
-		if (diff > max_sem_time) {
-			where = sanitize_str(where);
-			printk("max sem hold time %ld jiffies from %s "
-				"to %s\n", diff, adev->last_sem, where);
-			max_sem_time = diff;
-		}
-	}
-	up(&adev->sem);
-	if (acx_debug & L_LOCK) {
-		where = sanitize_str(where);
-		printk("%s: sem_up %d -> %d\n",
-			where, sem_count, atomic_read(&adev->sem.count));
-	}
-}
 #endif /* PARANOID_LOCKING */
 
 
diff --git a/pci.c b/pci.c
index 910155f..a390606 100644
--- a/pci.c
+++ b/pci.c
@@ -1617,7 +1617,7 @@ acxpci_e_probe(struct pci_dev *pdev, con
 	adev = ndev2adev(ndev);
 	spin_lock_init(&adev->lock);	/* initial state: unlocked */
 	/* We do not start with downed sem: we want PARANOID_LOCKING to work */
-	sema_init(&adev->sem, 1);	/* initial state: 1 (upped) */
+	mutex_init(&adev->mutex);	/* initial state: 1 (upped) */
 	/* since nobody can see new netdev yet, we can as well
 	** just _presume_ that we're under sem (instead of actually taking it): */
 	/* acx_sem_lock(adev); */
diff --git a/usb.c b/usb.c
index 3183743..cd610e4 100644
--- a/usb.c
+++ b/usb.c
@@ -869,7 +869,7 @@ acxusb_e_probe(struct usb_interface *int
 
 	adev->usbdev = usbdev;
 	spin_lock_init(&adev->lock);    /* initial state: unlocked */
-	sema_init(&adev->sem, 1);       /* initial state: 1 (upped) */
+	mutex_init(&adev->mutex);       /* initial state: 1 (upped) */
 
 	/* Check that this is really the hardware we know about.
 	** If not sure, at least notify the user that he