mtx: remove the stupid

include/gay/mutex.h

@@ -21,8 +21,8 @@ int spin_trylock(spin_t *spin);
 void spin_unlock(spin_t *spin);
 
 struct lock_waiter {
-	struct task *task;
 	struct clist clink;
+	struct task *task;
 };
 
 struct mtx {

kernel/mutex.c

@@ -40,32 +40,35 @@ void mtx_init(struct mtx *mtx)
 
 void mtx_lock(struct mtx *mtx)
 {
-	while (1) {
+	/*
+	 * acquire a lock on the wait queue before trying to claim the
+	 * mutex itself to make sure the mutex isn't released while we
+	 * are inserting ourselves into the wait queue
+	 */
+	spin_lock(&mtx->wait_queue_lock);
+	if (atom_write(&mtx->lock, 1) == 0) {
+		spin_unlock(&mtx->wait_queue_lock);
+	} else {
+		struct task *task = current;
 		/*
-		 * acquire a lock on the wait queue before trying to claim the
-		 * mutex itself to make sure the mutex isn't released while we
-		 * are inserting ourselves into the wait queue
+		 * It might not be the smartest idea to allocate this thing on
+		 * the stack because it's gonna blow up if the task somehow dies
+		 * before returning here.  Let's see how this turns out.
 		 */
-		spin_lock(&mtx->wait_queue_lock);
-		if (atom_write(&mtx->lock, 1) == 0) {
-			spin_unlock(&mtx->wait_queue_lock);
-			break;
-		} else {
-			struct task *cur = current;
-			/*
-			 * It might not be the smartest idea to allocate this thing on
-			 * the stack because it's gonna blow up if the task somehow dies
-			 * before returning here.  Let's see how this turns out.
-			 */
-			struct lock_waiter waiter = {
-				.task = cur,
-			};
-			clist_add(&mtx->wait_queue, &waiter.clink);
-			spin_unlock(&mtx->wait_queue_lock);
+		struct lock_waiter waiter = {
+			.task = task,
+		};
+		clist_add(&mtx->wait_queue, &waiter.clink);
+		spin_unlock(&mtx->wait_queue_lock);
 
-			cur->state = TASK_BLOCKED;
-			schedule();
-		}
+		task->state = TASK_BLOCKED;
+		/*
+		 * This is only gonna return when the task currently owning the
+		 * lock releases it.  In that case, it doesn't unlock the mutex
+		 * but merely switches back to us directly and thereby implicitly
+		 * transfers the ownership of the mutex to us (see mtx_unlock()).
+		 */
+		schedule();
 	}
 }