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Commit da54a0ce authored by Jiri Kosina's avatar Jiri Kosina
Browse files

HID: update BKL comment in hiddev 



Update comment explaining BKL usage in legacy hiddev driver.

Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 0a504541

drivers/hid/usbhid/hiddev.c

+17 −2
Original line number Original line Diff line number Diff line
@@ -267,6 +267,7 @@ static int hiddev_open(struct inode *inode, struct file *file) 
	struct hiddev_list *list;

	struct hiddev_list *list;

	int res, i;

	int res, i;





	/* See comment in hiddev_connect() for BKL explanation */

	lock_kernel();

	lock_kernel();

	i = iminor(inode) - HIDDEV_MINOR_BASE;

	i = iminor(inode) - HIDDEV_MINOR_BASE;
@@ -894,8 +895,22 @@ int hiddev_connect(struct hid_device *hid, unsigned int force) 
	hiddev->hid = hid;

	hiddev->hid = hid;

	hiddev->exist = 1;

	hiddev->exist = 1;





	/* when lock_kernel() usage is fixed in usb_open(),

	/*

	 * we could also fix it here */

	 * 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();

	lock_kernel();

	retval = usb_register_dev(usbhid->intf, &hiddev_class);

	retval = usb_register_dev(usbhid->intf, &hiddev_class);

	if (retval) {

	if (retval) {