On Wed, 23 May 2007, Oleg Nesterov wrote:
> On 05/23, Alan Stern wrote:
> >
> > Okay, it's clear that the two threads are in deadlock. It's not clear
> > how the deadlock arose to begin with -- apparently there was a remote
> > wakeup request for a root hub at the same time as a device below that
> > root hub was disconnected, which doesn't make much sense.
>
> Please note that this flush_workqueue() was not safe anyway. We are freezing
> tasks, and ksuspend_usb_wq is freezeable. So, it could be frozen before
> "khubd" task, and we have another deadlock.
Correct. I was planning to replace the flush_workqueue() anyway for
that very reason; this is a good excuse to do it.
> > Anyway, this looks like a good place to use cancel_work_sync(). The
>
> Could you use cancel_rearming_delayed_work() ? (It should be renamed to
> cancel_delayed_work_sync()).
Good idea. Here's a revised patch.
Alan Stern
Index: usb-2.6/drivers/usb/core/hub.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/hub.c
+++ usb-2.6/drivers/usb/core/hub.c
@@ -1228,6 +1228,30 @@ static void release_address(struct usb_d
}
}
+#ifdef CONFIG_USB_SUSPEND
+
+static void usb_stop_pm(struct usb_device *udev)
+{
+ /* Synchronize with the ksuspend thread to prevent any more
+ * autosuspend requests from being submitted, and decrement
+ * the parent's count of unsuspended children.
+ */
+ usb_pm_lock(udev);
+ if (udev->parent && !udev->discon_suspended)
+ usb_autosuspend_device(udev->parent);
+ usb_pm_unlock(udev);
+
+ /* Stop any autosuspend requests already submitted */
+ cancel_rearming_delayed_work(&udev->autosuspend);
+}
+
+#else
+
+static inline void usb_stop_pm(struct usb_device *udev)
+{ }
+
+#endif
+
/**
* usb_disconnect - disconnect a device (usbcore-internal)
* @pdev: pointer to device being disconnected
@@ -1294,14 +1318,7 @@ void usb_disconnect(struct usb_device **
*pdev = NULL;
spin_unlock_irq(&device_state_lock);
- /* Synchronize with the ksuspend thread to prevent any more
- * autosuspend requests from being submitted, and decrement
- * the parent's count of unsuspended children.
- */
- usb_pm_lock(udev);
- if (udev->parent && !udev->discon_suspended)
- usb_autosuspend_device(udev->parent);
- usb_pm_unlock(udev);
+ usb_stop_pm(udev);
put_device(&udev->dev);
}
Index: usb-2.6/drivers/usb/core/usb.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/usb.c
+++ usb-2.6/drivers/usb/core/usb.c
@@ -184,10 +184,6 @@ static void usb_release_dev(struct devic
udev = to_usb_device(dev);
-#ifdef CONFIG_USB_SUSPEND
- cancel_delayed_work(&udev->autosuspend);
- flush_workqueue(ksuspend_usb_wq);
-#endif
usb_destroy_configuration(udev);
usb_put_hcd(bus_to_hcd(udev->bus));
kfree(udev->product);
Index: usb-2.6/drivers/usb/core/hcd.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/hcd.c
+++ usb-2.6/drivers/usb/core/hcd.c
@@ -1683,7 +1683,7 @@ void usb_remove_hcd(struct usb_hcd *hcd)
spin_unlock_irq (&hcd_root_hub_lock);
#ifdef CONFIG_PM
- flush_workqueue(ksuspend_usb_wq);
+ cancel_work_sync(&hcd->wakeup_work);
#endif
mutex_lock(&usb_bus_list_lock);
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