HID: hiddev: use usb_find_interface, get rid of BKL

This removes the private hiddev_table in the usbhid
driver and changes it to use usb_find_interface
instead.

The advantage is that we can avoid the race between
usb_register_dev and usb_open and no longer need the
big kernel lock.

This doesn't introduce race condition -- the intf pointer could be
invalidated only in hiddev_disconnect() through usb_deregister_dev(),
but that will block on minor_rwsem and not actually remove the device
until usb_open().

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "Greg Kroah-Hartman" <gregkh@suse.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/usbhid/hiddev.c b/drivers/hid/usbhid/hiddev.c
index c24d2fa3e3b607d6bb5b85e15fffb4cedcfdb4af..254a003af048dd7a909e68f4a96ffcaae391bc96 100644 (file)
--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -67,7 +67,7 @@ struct hiddev_list {
        struct mutex thread_lock;
 };
 
-static struct hiddev *hiddev_table[HIDDEV_MINORS];
+static struct usb_driver hiddev_driver;
 
 /*
  * Find a report, given the report's type and ID.  The ID can be specified
@@ -265,22 +265,19 @@ static int hiddev_release(struct inode * inode, struct file * file)
 static int hiddev_open(struct inode *inode, struct file *file)
 {
        struct hiddev_list *list;
-       int res, i;
-
-       /* See comment in hiddev_connect() for BKL explanation */
-       lock_kernel();
-       i = iminor(inode) - HIDDEV_MINOR_BASE;
+       struct usb_interface *intf;
+       struct hiddev *hiddev;
+       int res;
 
-       if (i >= HIDDEV_MINORS || i < 0 || !hiddev_table[i])
+       intf = usb_find_interface(&hiddev_driver, iminor(inode));
+       if (!intf)
                return -ENODEV;
+       hiddev = usb_get_intfdata(intf);
 
        if (!(list = kzalloc(sizeof(struct hiddev_list), GFP_KERNEL)))
                return -ENOMEM;
        mutex_init(&list->thread_lock);
-
-       list->hiddev = hiddev_table[i];
-
-
+       list->hiddev = hiddev;
        file->private_data = list;
 
        /*
@@ -289,7 +286,7 @@ static int hiddev_open(struct inode *inode, struct file *file)
         */
        if (list->hiddev->exist) {
                if (!list->hiddev->open++) {
-                       res = usbhid_open(hiddev_table[i]->hid);
+                       res = usbhid_open(hiddev->hid);
                        if (res < 0) {
                                res = -EIO;
                                goto bail;
@@ -301,12 +298,12 @@ static int hiddev_open(struct inode *inode, struct file *file)
        }
 
        spin_lock_irq(&list->hiddev->list_lock);
-       list_add_tail(&list->node, &hiddev_table[i]->list);
+       list_add_tail(&list->node, &hiddev->list);
        spin_unlock_irq(&list->hiddev->list_lock);
 
        if (!list->hiddev->open++)
                if (list->hiddev->exist) {
-                       struct hid_device *hid = hiddev_table[i]->hid;
+                       struct hid_device *hid = hiddev->hid;
                        res = usbhid_get_power(hid);
                        if (res < 0) {
                                res = -EIO;
@@ -314,13 +311,10 @@ static int hiddev_open(struct inode *inode, struct file *file)
                        }
                        usbhid_open(hid);
                }
-
-       unlock_kernel();
        return 0;
 bail:
        file->private_data = NULL;
        kfree(list);
-       unlock_kernel();
        return res;
 }
 
@@ -894,37 +888,14 @@ int hiddev_connect(struct hid_device *hid, unsigned int force)
        hid->hiddev = hiddev;
        hiddev->hid = hid;
        hiddev->exist = 1;
-
-       /*
-        * BKL here is used to avoid race after usb_register_dev().
-        * Once the device node has been created, open() could happen on it.
-        * The code below will then fail, as hiddev_table hasn't been
-        * updated.
-        *
-        * The obvious fix -- introducing mutex to guard hiddev_table[]
-        * doesn't work, as usb_open() and usb_register_dev() both take
-        * minor_rwsem, thus we'll have ABBA deadlock.
-        *
-        * Before BKL pushdown, usb_open() had been acquiring it in right
-        * order, so _open() was safe to use it to protect from this race.
-        * Now the order is different, but AB-BA deadlock still doesn't occur
-        * as BKL is dropped on schedule() (i.e. while sleeping on
-        * minor_rwsem). Fugly.
-        */
-       lock_kernel();
+       usb_set_intfdata(usbhid->intf, usbhid);
        retval = usb_register_dev(usbhid->intf, &hiddev_class);
        if (retval) {
                err_hid("Not able to get a minor for this device.");
                hid->hiddev = NULL;
-               unlock_kernel();
                kfree(hiddev);
                return -1;
-       } else {
-               hid->minor = usbhid->intf->minor;
-               hiddev_table[usbhid->intf->minor - HIDDEV_MINOR_BASE] = hiddev;
        }
-       unlock_kernel();
-
        return 0;
 }
 
@@ -942,7 +913,6 @@ void hiddev_disconnect(struct hid_device *hid)
        hiddev->exist = 0;
        mutex_unlock(&hiddev->existancelock);
 
-       hiddev_table[hiddev->hid->minor - HIDDEV_MINOR_BASE] = NULL;
        usb_deregister_dev(usbhid->intf, &hiddev_class);
 
        if (hiddev->open) {