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HID: hiddev: use usb_find_interface, get rid of BKL

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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>
This commit is contained in:
Arnd Bergmann 2010-07-11 15:34:05 +02:00 committed by Jiri Kosina
parent 1c5474a65b
commit bd25f4dd69
1 changed files with 12 additions and 42 deletions
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54
drivers/hid/usbhid/hiddev.c
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@ -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;
struct usb_interface *intf;
struct hiddev *hiddev;
int res;
/* See comment in hiddev_connect() for BKL explanation */
lock_kernel();
i = iminor(inode) - HIDDEV_MINOR_BASE;
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) {