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HID: update BKL comment in hiddev

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Update comment explaining BKL usage in legacy hiddev driver.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Jiri Kosina 2010-03-25 15:34:34 +01:00
parent 0a504541b3
commit da54a0ced4
1 changed files with 17 additions and 2 deletions
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19
drivers/hid/usbhid/hiddev.c
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@ -267,6 +267,7 @@ 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;
@ -894,8 +895,22 @@ int hiddev_connect(struct hid_device *hid, unsigned int force)
hiddev->hid = hid;
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();
retval = usb_register_dev(usbhid->intf, &hiddev_class);
if (retval) {