Commit 62e299e6 authored by Alan Stern's avatar Alan Stern Committed by Greg Kroah-Hartman
Browse files

USB: change locking for device-level autosuspend 



This patch (as1323) changes the locking requirements for
usb_autosuspend_device(), usb_autoresume_device(), and
usb_try_autosuspend_device().  This isn't a very important change;
mainly it's meant to make the locking more uniform.

The most tricky part of the patch involves changes to usbdev_open().
To avoid an ABBA locking problem, it was necessary to reduce the
region protected by usbfs_mutex.  Since that mutex now protects only
against simultaneous open and remove, this posed no difficulty -- its
scope was larger than necessary.

And it turns out that usbfs_mutex is no longer needed in
usbdev_release() at all.  The list of usbfs "ps" structures is now
protected by the device lock instead of by usbfs_mutex.

Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 0f3dda9f

drivers/usb/core/devio.c

+24 −16
Original line number Diff line number Diff line
@@ -654,19 +654,21 @@ static int usbdev_open(struct inode *inode, struct file *file) 
	int ret;



	lock_kernel();

	/* Protect against simultaneous removal or release */

	mutex_lock(&usbfs_mutex);



	ret = -ENOMEM;

	ps = kmalloc(sizeof(struct dev_state), GFP_KERNEL);

	if (!ps)

		goto out;

		goto out_free_ps;



	ret = -ENODEV;



	/* Protect against simultaneous removal or release */

	mutex_lock(&usbfs_mutex);



	/* usbdev device-node */

	if (imajor(inode) == USB_DEVICE_MAJOR)

		dev = usbdev_lookup_by_devt(inode->i_rdev);



#ifdef CONFIG_USB_DEVICEFS

	/* procfs file */

	if (!dev) {
@@ -678,13 +680,19 @@ static int usbdev_open(struct inode *inode, struct file *file) 
			dev = NULL;

	}

#endif

	if (!dev || dev->state == USB_STATE_NOTATTACHED)

		goto out;

	mutex_unlock(&usbfs_mutex);



	if (!dev)

		goto out_free_ps;



	usb_lock_device(dev);

	if (dev->state == USB_STATE_NOTATTACHED)

		goto out_unlock_device;



	ret = usb_autoresume_device(dev);

	if (ret)

		goto out;

		goto out_unlock_device;



	ret = 0;

	ps->dev = dev;

	ps->file = file;

	spin_lock_init(&ps->lock);
@@ -702,14 +710,17 @@ static int usbdev_open(struct inode *inode, struct file *file) 
	smp_wmb();

	list_add_tail(&ps->list, &dev->filelist);

	file->private_data = ps;

	usb_unlock_device(dev);

	snoop(&dev->dev, "opened by process %d: %s\n", task_pid_nr(current),

			current->comm);

 out:

	if (ret) {

		kfree(ps);

	unlock_kernel();

	return ret;



 out_unlock_device:

	usb_unlock_device(dev);

	usb_put_dev(dev);

	}

	mutex_unlock(&usbfs_mutex);

 out_free_ps:

	kfree(ps);

	unlock_kernel();

	return ret;

}
@@ -724,10 +735,7 @@ static int usbdev_release(struct inode *inode, struct file *file) 
	usb_lock_device(dev);

	usb_hub_release_all_ports(dev, ps);



	/* Protect against simultaneous open */

	mutex_lock(&usbfs_mutex);

	list_del_init(&ps->list);

	mutex_unlock(&usbfs_mutex);



	for (ifnum = 0; ps->ifclaimed && ifnum < 8*sizeof(ps->ifclaimed);

			ifnum++) {

drivers/usb/core/driver.c

+4 −4
Original line number Diff line number Diff line
@@ -1478,8 +1478,7 @@ void usb_autoresume_work(struct work_struct *work) 
 * driver requires remote-wakeup capability during autosuspend but remote

 * wakeup is disabled, the autosuspend will fail.

 *

 * Often the caller will hold @udev's device lock, but this is not

 * necessary.

 * The caller must hold @udev's device lock.

 *

 * This routine can run only in process context.

 */
@@ -1503,6 +1502,8 @@ void usb_autosuspend_device(struct usb_device *udev) 
 * for an active interface is greater than 0, or autosuspend is not allowed

 * for any other reason, no autosuspend request will be queued.

 *

 * The caller must hold @udev's device lock.

 *

 * This routine can run only in process context.

 */

void usb_try_autosuspend_device(struct usb_device *udev)
@@ -1526,8 +1527,7 @@ void usb_try_autosuspend_device(struct usb_device *udev) 
 * @udev's usage counter is incremented to prevent subsequent autosuspends.

 * However if the autoresume fails then the usage counter is re-decremented.

 *

 * Often the caller will hold @udev's device lock, but this is not

 * necessary (and attempting it might cause deadlock).

 * The caller must hold @udev's device lock.

 *

 * This routine can run only in process context.

 */

drivers/usb/core/sysfs.c

+2 −0
Original line number Diff line number Diff line
@@ -352,6 +352,7 @@ set_autosuspend(struct device *dev, struct device_attribute *attr, 
		return -EINVAL;

	value *= HZ;



	usb_lock_device(udev);

	udev->autosuspend_delay = value;

	if (value >= 0)

		usb_try_autosuspend_device(udev);
@@ -359,6 +360,7 @@ set_autosuspend(struct device *dev, struct device_attribute *attr, 
		if (usb_autoresume_device(udev) == 0)

			usb_autosuspend_device(udev);

	}

	usb_unlock_device(udev);

	return count;

}

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