From bd7db3a7ec4c1d4dee0aa7ef53c547cb353ad2ee Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@dragonflybsd.org>
Date: Mon, 21 Apr 2008 15:23:22 +0000
Subject: [PATCH] Add an interlock for certain usb task operations.

---
 sys/bus/usb/usb.c | 67 ++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 51 insertions(+), 16 deletions(-)

diff --git a/sys/bus/usb/usb.c b/sys/bus/usb/usb.c
index b7517ccc67..fbdc8fd875 100644
--- a/sys/bus/usb/usb.c
+++ b/sys/bus/usb/usb.c
@@ -1,7 +1,7 @@
 /*
  * $NetBSD: usb.c,v 1.68 2002/02/20 20:30:12 christos Exp $
  * $FreeBSD: src/sys/dev/usb/usb.c,v 1.106 2005/03/27 15:31:23 iedowse Exp $
- * $DragonFly: src/sys/bus/usb/usb.c,v 1.39 2007/07/03 19:28:16 hasso Exp $
+ * $DragonFly: src/sys/bus/usb/usb.c,v 1.40 2008/04/21 15:23:22 dillon Exp $
  */
 
 /* Also already merged from NetBSD:
@@ -368,15 +368,21 @@ usb_add_task(usbd_device_handle dev, struct usb_task *task, int queue)
 
 	crit_enter();
 
+	/*
+	 * Wait if task is currently executing
+	 */
+	while (task->queue == -2)
+		tsleep(task, 0, "usbwttsk", hz);
+
 	taskq = &usb_taskq[queue];
 	if (task->queue == -1) {
 		DPRINTFN(2,("usb_add_task: task=%p\n", task));
 		TAILQ_INSERT_TAIL(&taskq->tasks, task, next);
 		task->queue = queue;
+		wakeup(&taskq->tasks);
 	} else {
 		DPRINTFN(3,("usb_add_task: task=%p on q\n", task));
 	}
-	wakeup(&taskq->tasks);
 
 	crit_exit();
 }
@@ -389,18 +395,27 @@ usb_do_task(usbd_device_handle dev, struct usb_task *task, int queue,
 
 	crit_enter();
 
+	/*
+	 * Wait if task is currently executing
+	 */
+	while (task->queue == -2)
+		tsleep(task, 0, "usbwttsk", hz);
+
 	taskq = &usb_taskq[queue];
 	if (task->queue == -1) {
 		DPRINTFN(2,("usb_add_task: task=%p\n", task));
 		TAILQ_INSERT_TAIL(&taskq->tasks, task, next);
 		task->queue = queue;
+		wakeup(&taskq->tasks);
 	} else {
 		DPRINTFN(3,("usb_add_task: task=%p on q\n", task));
 	}
-	wakeup(&taskq->tasks);
 
-	/* Wait until task is finished */
-	tsleep((&taskq->tasks + 1), 0, "usbdotsk", time_out);
+	/*
+	 * Wait until task is completely finished
+	 */
+	while (task->queue != -1)
+		tsleep(task, 0, "usbwttsk", hz);
 
 	crit_exit();
 }
@@ -409,6 +424,16 @@ void
 usb_rem_task(usbd_device_handle dev, struct usb_task *task)
 {
 	crit_enter();
+
+	/*
+	 * Wait if task is currently executing, we can't remove it now!
+	 */
+	while (task->queue == -2)
+		tsleep(task, 0, "usbwttsk", hz);
+
+	/*
+	 * Remove the task if it has not started executing yet.
+	 */
 	if (task->queue != -1) {
 		TAILQ_REMOVE(&usb_taskq[task->queue].tasks, task, next);
 		task->queue = -1;
@@ -475,20 +500,30 @@ usb_task_thread(void *arg)
 	DPRINTF(("usb_task_thread: start taskq %s\n", taskq->name));
 
 	while (usb_ndevs > 0) {
-		task = TAILQ_FIRST(&taskq->tasks);
-		if (task == NULL) {
+		/*
+		 * Wait for work
+		 */
+		if ((task = TAILQ_FIRST(&taskq->tasks)) == NULL) {
 			tsleep(&taskq->tasks, 0, "usbtsk", 0);
-			task = TAILQ_FIRST(&taskq->tasks);
+			continue;
 		}
+
+		/*
+		 * De-queue, mark as currently executing and run the
+		 * function.
+		 */
 		DPRINTFN(2,("usb_task_thread: woke up task=%p\n", task));
-		if (task != NULL) {
-			TAILQ_REMOVE(&taskq->tasks, task, next);
-			task->queue = -1;
-			crit_exit();
-			task->fun(task->arg);
-			crit_enter();
-			wakeup((&taskq->tasks + 1));
-		}
+		TAILQ_REMOVE(&taskq->tasks, task, next);
+		task->queue = -2;
+		crit_exit();
+		task->fun(task->arg);
+
+		/*
+		 * Mark as complete and wakeup anyone waiting.
+		 */
+		crit_enter();
+		task->queue = -1;
+		wakeup(task);
 	}
 
 	crit_exit();
-- 
2.41.0