Alan Stern wrote:
>
> I recently sent in a patch that removes the BKL from usbdev_open:
>
> http://marc.theaimsgroup.com/?l=linux-usb-devel&m=115074414607596&w=2
>
ok it seems you did the job for usbdev_open(). But one thing I fail to
understand is:
"""
Yet another problem arises because the same file_operations structure is
accessible through both the /proc/bus/usb/* and /dev/usb/usbdev* file
nodes. Even when one of them has been removed, it's still possible for
userspace to open the other. So simple locking around the individual
remove routines is insufficient; we need to lock the entire
usb_notify_remove_device notifier chain.
"""
One other question is does usbdev_remove() really acquire the device
lock ?
> I didn't notice that it was used in usbdev_lseek and there doesn't seem to
> be any reason for it to be there. Nor does there seem to be any reason
> for it in usb_device_lseek.
>
> The code in usb_device_poll probably should be revised in view of the
> changes in my patch. You might want to look at that. But you're right,
> it shouldn't be using the BKL.
>
are we talking about the same thing here ? I was speaking about
usb_device_poll() in devices.c, and it seems you're talking about
usbdev_poll() which is in devio.c.
> Likewise, uhci-debug doesn't need to use the BKL either. It can simply be
> removed from that routine.
ok I'll take a look.
>
> The use of BKL in usb-skeleton and possibly some of the other drivers
> follows a simple pattern. It is there to prevent races between open() and
> disconnect(). The idea is that the kernel automatically acquires the BKL
> whenever a character device node is opened, so by taking the lock in the
> disconnect routine we avoid the problem of people opening a device file
> as it is being unregistered.
>
can we just use the device's lock for that purpose ?
Franck
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