Re: [PATCH] USB: replace flush_workqueue with cancel_sync_work

Mark Lord
2007-05-29T21:20:16Z

Thanks again, Alan!

From: Alan Stern <stern@rowland.harvard.edu>
>
>This patch (as912) replaces a couple of calls to flush_workqueue()
>with cancel_sync_work() and cancel_rearming_delayed_work(). Using a
>more directed approach allows us to avoid some nasty deadlocks. The
>prime example occurs when a first-level device (the parent is a root
>hub) is removed while at the same time the root hub gets a remote
>wakeup request. khubd would try to flush the autosuspend workqueue
>while holding the root-hub's lock, and the remote-wakeup workqueue
>routine would be waiting to lock the root hub.
>
>The patch also reorganizes the power management portion of
>usb_disconnect(), separating it out into its own routine. The
>autosuspend workqueue entry is cancelled immediately instead of
>waiting for the device's release routine. In addition,
>synchronization with the autosuspend thread is carried out even for
>root hubs (an oversight in the original code).
>
>Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Mark Lord <mlord@pobox.com>

---

Index: 2.6.22-rc3/drivers/usb/core/hub.c
===================================================================
--- 2.6.22-rc3.orig/drivers/usb/core/hub.c
+++ 2.6.22-rc3/drivers/usb/core/hub.c
@@ -1158,6 +1158,30 @@ 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
@@ -1224,13 +1248,7 @@ void usb_disconnect(struct usb_device **
*pdev = NULL;
spin_unlock_irq(&device_state_lock);

- /* Decrement the parent's count of unsuspended children */
- if (udev->parent) {
- usb_pm_lock(udev);
- if (!udev->discon_suspended)
- usb_autosuspend_device(udev->parent);
- usb_pm_unlock(udev);
- }
+ usb_stop_pm(udev);

put_device(&udev->dev);
}
Index: 2.6.22-rc3/drivers/usb/core/usb.c
===================================================================
--- 2.6.22-rc3.orig/drivers/usb/core/usb.c
+++ 2.6.22-rc3/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: 2.6.22-rc3/drivers/usb/core/hcd.c
===================================================================
--- 2.6.22-rc3.orig/drivers/usb/core/hcd.c
+++ 2.6.22-rc3/drivers/usb/core/hcd.c
@@ -1681,7 +1681,7 @@ 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);

-