usb: core: hcd: Convert from tasklet to BH workqueue

The only generic interface to execute asynchronously in the BH context is
tasklet; however, it's marked deprecated and has some design flaws. To
replace tasklets, BH workqueue support was recently added. A BH workqueue
behaves similarly to regular workqueues except that the queued work items
are executed in the BH context.

This patch converts usb hcd from tasklet to BH workqueue.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-usb@vger.kernel.org

Author: htejun

drivers/usb/core/hcd.c

@@ -1664,9 +1664,10 @@ static void __usb_hcd_giveback_urb(struct urb *urb)
 	usb_put_urb(urb);
 }
 
-static void usb_giveback_urb_bh(struct tasklet_struct *t)
+static void usb_giveback_urb_bh(struct work_struct *work)
 {
-	struct giveback_urb_bh *bh = from_tasklet(bh, t, bh);
+	struct giveback_urb_bh *bh =
+		container_of(work, struct giveback_urb_bh, bh);
 	struct list_head local_list;
 
 	spin_lock_irq(&bh->lock);
@@ -1691,9 +1692,9 @@ static void usb_giveback_urb_bh(struct tasklet_struct *t)
 	spin_lock_irq(&bh->lock);
 	if (!list_empty(&bh->head)) {
 		if (bh->high_prio)
-			tasklet_hi_schedule(&bh->bh);
+			queue_work(system_bh_highpri_wq, &bh->bh);
 		else
-			tasklet_schedule(&bh->bh);
+			queue_work(system_bh_wq, &bh->bh);
 	}
 	bh->running = false;
 	spin_unlock_irq(&bh->lock);
@@ -1706,7 +1707,7 @@ static void usb_giveback_urb_bh(struct tasklet_struct *t)
  * @status: completion status code for the URB.
  *
  * Context: atomic. The completion callback is invoked in caller's context.
- * For HCDs with HCD_BH flag set, the completion callback is invoked in tasklet
+ * For HCDs with HCD_BH flag set, the completion callback is invoked in BH
  * context (except for URBs submitted to the root hub which always complete in
  * caller's context).
  *
@@ -1725,7 +1726,7 @@ void usb_hcd_giveback_urb(struct usb_hcd *hcd, struct urb *urb, int status)
 	struct giveback_urb_bh *bh;
 	bool running;
 
-	/* pass status to tasklet via unlinked */
+	/* pass status to BH via unlinked */
 	if (likely(!urb->unlinked))
 		urb->unlinked = status;
 
@@ -1747,9 +1748,9 @@ void usb_hcd_giveback_urb(struct usb_hcd *hcd, struct urb *urb, int status)
 	if (running)
 		;
 	else if (bh->high_prio)
-		tasklet_hi_schedule(&bh->bh);
+		queue_work(system_bh_highpri_wq, &bh->bh);
 	else
-		tasklet_schedule(&bh->bh);
+		queue_work(system_bh_wq, &bh->bh);
 }
 EXPORT_SYMBOL_GPL(usb_hcd_giveback_urb);
 
@@ -2540,7 +2541,7 @@ static void init_giveback_urb_bh(struct giveback_urb_bh *bh)
 
 	spin_lock_init(&bh->lock);
 	INIT_LIST_HEAD(&bh->head);
-	tasklet_setup(&bh->bh, usb_giveback_urb_bh);
+	INIT_WORK(&bh->bh, usb_giveback_urb_bh);
 }
 
 struct usb_hcd *__usb_create_hcd(const struct hc_driver *driver,
@@ -2926,7 +2927,7 @@ int usb_add_hcd(struct usb_hcd *hcd,
 			&& device_can_wakeup(&hcd->self.root_hub->dev))
 		dev_dbg(hcd->self.controller, "supports USB remote wakeup\n");
 
-	/* initialize tasklets */
+	/* initialize BHs */
 	init_giveback_urb_bh(&hcd->high_prio_bh);
 	hcd->high_prio_bh.high_prio = true;
 	init_giveback_urb_bh(&hcd->low_prio_bh);
@@ -3036,7 +3037,7 @@ void usb_remove_hcd(struct usb_hcd *hcd)
 	mutex_unlock(&usb_bus_idr_lock);
 
 	/*
-	 * tasklet_kill() isn't needed here because:
+	 * flush_work() isn't needed here because:
 	 * - driver's disconnect() called from usb_disconnect() should
 	 *   make sure its URBs are completed during the disconnect()
 	 *   callback

include/linux/usb/hcd.h

@@ -55,7 +55,7 @@ struct giveback_urb_bh {
 	bool high_prio;
 	spinlock_t lock;
 	struct list_head  head;
-	struct tasklet_struct bh;
+	struct work_struct bh;
 	struct usb_host_endpoint *completing_ep;
 };