Tidy up the thread taskqueue implementation and close a lost wakeup race.

Instead of creating a mutex that we msleep on but don't actually lock when
doing the corresponding wakeup(), in the kthread, lock the mutex associated
with our taskqueue and msleep while the queue is empty.  Assert that the
queue is locked when the callback function is called to wake the kthread.

1 files changed, 9 insertions, 14 deletions

diff --git a/sys/kern/subr_taskqueue.c b/sys/kern/subr_taskqueue.c
index aeebd08..953300a 100644
--- a/sys/kern/subr_taskqueue.c
+++ b/sys/kern/subr_taskqueue.c
@@ -235,28 +235,23 @@ taskqueue_swi_giant_run(void *dummy)
 }
 
 static void
-taskqueue_kthread(void *arg)
+taskqueue_thread_loop(void *arg)
 {
-	struct mtx kthread_mutex;
-
-	bzero(&kthread_mutex, sizeof(kthread_mutex));
-
-	mtx_init(&kthread_mutex, "taskqueue kthread", NULL, MTX_DEF);
-
-	mtx_lock(&kthread_mutex);
-
 	for (;;) {
-		mtx_unlock(&kthread_mutex);
+		mtx_lock(&taskqueue_thread->tq_mutex);
+		while (STAILQ_EMPTY(&taskqueue_thread->tq_queue))
+			msleep(taskqueue_thread, &taskqueue_thread->tq_mutex,
+			    PWAIT, "-", 0); 
+		mtx_unlock(&taskqueue_thread->tq_mutex);
 		taskqueue_run(taskqueue_thread);
-		mtx_lock(&kthread_mutex);
-		msleep(&taskqueue_thread, &kthread_mutex, PWAIT, "tqthr", 0); 
 	}
 }
 
 static void
 taskqueue_thread_enqueue(void *context)
 {
-	wakeup(&taskqueue_thread);
+	mtx_assert(&taskqueue_thread->tq_mutex, MA_OWNED);
+	wakeup(taskqueue_thread);
 }
 
 TASKQUEUE_DEFINE(swi, taskqueue_swi_enqueue, 0,
@@ -268,7 +263,7 @@ TASKQUEUE_DEFINE(swi_giant, taskqueue_swi_giant_enqueue, 0,
 		     NULL, SWI_TQ_GIANT, 0, &taskqueue_giant_ih)); 
 
 TASKQUEUE_DEFINE(thread, taskqueue_thread_enqueue, 0,
-		 kthread_create(taskqueue_kthread, NULL,
+		 kthread_create(taskqueue_thread_loop, NULL,
 		 &taskqueue_thread_proc, 0, 0, "taskqueue"));
 
 int