[PATCH redone and resent] usbhid: prevent deadlock during timeout

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>From 4716d3af512c005b1978f343cb9f26ef71488ce1 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oliver@xxxxxxxxxx>
Date: Mon, 30 Apr 2012 09:13:46 +0200
Subject: [PATCH] usbhid: prevent deadlock during timeout

On some HCDs usb_unlink_urb() can directly call the
completion handler. That limits the spinlocks that can
be taken in the handler to locks not held while calling
usb_unlink_urb()
To prevent a race with resubmission, this patch exposes
usbcore's infrastructure for blocking submission, uses it
and so drops the lock without causing a race in usbhid.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxx>
---
 drivers/hid/usbhid/hid-core.c |   61 +++++++++++++++++++++++++++++++++++++----
 drivers/usb/core/urb.c        |   21 ++++++++++++++
 include/linux/usb.h           |    3 ++
 3 files changed, 79 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/usbhid/hid-core.c b/drivers/hid/usbhid/hid-core.c
index 5bf91db..c8eab8d 100644
--- a/drivers/hid/usbhid/hid-core.c
+++ b/drivers/hid/usbhid/hid-core.c
@@ -399,6 +399,16 @@ static int hid_submit_ctrl(struct hid_device *hid)
  * Output interrupt completion handler.
  */
 
+static int irq_out_pump_restart(struct hid_device *hid)
+{
+	struct usbhid_device *usbhid = hid->driver_data;
+
+	if (usbhid->outhead != usbhid->outtail)
+		return hid_submit_out(hid);
+	else
+		return -1;
+}
+
 static void hid_irq_out(struct urb *urb)
 {
 	struct hid_device *hid = urb->context;
@@ -428,7 +438,7 @@ static void hid_irq_out(struct urb *urb)
 	else
 		usbhid->outtail = (usbhid->outtail + 1) & (HID_OUTPUT_FIFO_SIZE - 1);
 
-	if (usbhid->outhead != usbhid->outtail && !hid_submit_out(hid)) {
+	if (!irq_out_pump_restart(hid)) {
 		/* Successfully submitted next urb in queue */
 		spin_unlock_irqrestore(&usbhid->lock, flags);
 		return;
@@ -443,6 +453,15 @@ static void hid_irq_out(struct urb *urb)
 /*
  * Control pipe completion handler.
  */
+static int ctrl_pump_restart(struct hid_device *hid)
+{
+	struct usbhid_device *usbhid = hid->driver_data;
+
+        if (usbhid->ctrlhead != usbhid->ctrltail)
+		return hid_submit_ctrl(hid);
+	else
+		return -1;
+}
 
 static void hid_ctrl(struct urb *urb)
 {
@@ -476,7 +495,7 @@ static void hid_ctrl(struct urb *urb)
 	else
 		usbhid->ctrltail = (usbhid->ctrltail + 1) & (HID_CONTROL_FIFO_SIZE - 1);
 
-	if (usbhid->ctrlhead != usbhid->ctrltail && !hid_submit_ctrl(hid)) {
+	if (!ctrl_pump_restart(hid)) {
 		/* Successfully submitted next urb in queue */
 		spin_unlock(&usbhid->lock);
 		return;
@@ -535,11 +554,27 @@ static void __usbhid_submit_report(struct hid_device *hid, struct hid_report *re
 			 * the queue is known to run
 			 * but an earlier request may be stuck
 			 * we may need to time out
-			 * no race because this is called under
+			 * no race because the URB is blocked under
 			 * spinlock
 			 */
-			if (time_after(jiffies, usbhid->last_out + HZ * 5))
+			if (time_after(jiffies, usbhid->last_out + HZ * 5)) {
+				usb_block_urb(usbhid->urbout);
+				/* drop lock to not deadlock if the callback is called */
+				spin_unlock(&usbhid->lock);
 				usb_unlink_urb(usbhid->urbout);
+				spin_lock(&usbhid->lock);
+				usb_unblock_urb(usbhid->urbout);
+				/*
+				 * if the unlinking has already completed
+				 * the pump will have been stopped
+				 * it must be restarted now
+				 */
+				if (!test_bit(HID_OUT_RUNNING, &usbhid->iofl))
+					if (!irq_out_pump_restart(hid))
+						set_bit(HID_OUT_RUNNING, &usbhid->iofl);
+					
+
+			}
 		}
 		return;
 	}
@@ -583,11 +618,25 @@ static void __usbhid_submit_report(struct hid_device *hid, struct hid_report *re
 		 * the queue is known to run
 		 * but an earlier request may be stuck
 		 * we may need to time out
-		 * no race because this is called under
+		 * no race because the URB is blocked under
 		 * spinlock
 		 */
-		if (time_after(jiffies, usbhid->last_ctrl + HZ * 5))
+		if (time_after(jiffies, usbhid->last_ctrl + HZ * 5)) {
+			usb_block_urb(usbhid->urbctrl);
+			/* drop lock to not deadlock if the callback is called */
+			spin_unlock(&usbhid->lock);
 			usb_unlink_urb(usbhid->urbctrl);
+			spin_lock(&usbhid->lock);
+			usb_unblock_urb(usbhid->urbctrl);
+			/*
+			 * if the unlinking has already completed
+			 * the pump will have been stopped
+			 * it must be restarted now
+			 */
+			if (!test_bit(HID_CTRL_RUNNING, &usbhid->iofl))
+				if (!ctrl_pump_restart(hid))
+					set_bit(HID_CTRL_RUNNING, &usbhid->iofl);
+		}
 	}
 }
 
diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index cd9b3a2..c6b67c3 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -681,6 +681,27 @@ void usb_unpoison_urb(struct urb *urb)
 EXPORT_SYMBOL_GPL(usb_unpoison_urb);
 
 /**
+ * usb_block_urb - reliably prevent further use of an URB
+ * @urb: pointer to URB to be blocked, may be NULL
+ *
+ * After the routine has run, attempts to resubmit the URB will fail
+ * with error -EPERM.  Thus even if the URB's completion handler always
+ * tries to resubmit, it will not succeed and the URB will become idle.
+ *
+ * The URB must not be deallocated while this routine is running.  In
+ * particular, when a driver calls this routine, it must insure that the
+ * completion handler cannot deallocate the URB.
+ */
+void usb_block_urb(struct urb *urb)
+{
+        if (!urb)
+                return;
+
+        atomic_inc(&urb->reject);
+}
+EXPORT_SYMBOL_GPL(usb_block_urb);
+
+/**
  * usb_kill_anchored_urbs - cancel transfer requests en masse
  * @anchor: anchor the requests are bound to
  *
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 73b68d1..26229fd 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1379,6 +1379,7 @@ extern int usb_unlink_urb(struct urb *urb);
 extern void usb_kill_urb(struct urb *urb);
 extern void usb_poison_urb(struct urb *urb);
 extern void usb_unpoison_urb(struct urb *urb);
+extern void usb_block_urb(struct urb *urb);
 extern void usb_kill_anchored_urbs(struct usb_anchor *anchor);
 extern void usb_poison_anchored_urbs(struct usb_anchor *anchor);
 extern void usb_unpoison_anchored_urbs(struct usb_anchor *anchor);
@@ -1391,6 +1392,8 @@ extern struct urb *usb_get_from_anchor(struct usb_anchor *anchor);
 extern void usb_scuttle_anchored_urbs(struct usb_anchor *anchor);
 extern int usb_anchor_empty(struct usb_anchor *anchor);
 
+#define usb_unblock_urb	usb_unpoison_urb
+
 /**
  * usb_urb_dir_in - check if an URB describes an IN transfer
  * @urb: URB to be checked
-- 
1.7.1

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