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: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
---
Index: usb-2.6/drivers/usb/core/driver.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/driver.c
+++ usb-2.6/drivers/usb/core/driver.c
@@ -1470,8 +1470,7 @@ void usb_autoresume_work(struct work_str
* 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.
*/
@@ -1495,6 +1494,8 @@ void usb_autosuspend_device(struct usb_d
* 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)
@@ -1518,8 +1519,7 @@ void usb_try_autosuspend_device(struct u
* @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.
*/
Index: usb-2.6/drivers/usb/core/sysfs.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/sysfs.c
+++ usb-2.6/drivers/usb/core/sysfs.c
@@ -346,6 +346,7 @@ set_autosuspend(struct device *dev, stru
return -EINVAL;
value *= HZ;
+ usb_lock_device(udev);
udev->autosuspend_delay = value;
if (value >= 0)
usb_try_autosuspend_device(udev);
@@ -353,6 +354,7 @@ set_autosuspend(struct device *dev, stru
if (usb_autoresume_device(udev) == 0)
usb_autosuspend_device(udev);
}
+ usb_unlock_device(udev);
return count;
}
Index: usb-2.6/drivers/usb/core/devio.c
===================================================================
--- usb-2.6.orig/drivers/usb/core/devio.c
+++ usb-2.6/drivers/usb/core/devio.c
@@ -654,19 +654,21 @@ static int usbdev_open(struct inode *ino
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 *ino
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 *ino
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);
- usb_put_dev(dev);
- }
- mutex_unlock(&usbfs_mutex);
+ unlock_kernel();
+ return ret;
+
+ out_unlock_device:
+ usb_unlock_device(dev);
+ usb_put_dev(dev);
+ out_free_ps:
+ kfree(ps);
unlock_kernel();
return ret;
}
@@ -724,10 +735,7 @@ static int usbdev_release(struct inode *
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++) {
--
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