Messages in this thread | | | From | Oliver Neukum <> | Subject | Re: Possible race condition in usb-serial.c | Date | Wed, 20 Dec 2006 10:47:20 +0100 |
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Am Dienstag, 19. Dezember 2006 23:33 schrieb J: > Thank you for the response. > > > This code depends on protection from BKL. > > Really? I cannot find many lock_kernel calls in > USB directory and those, which I can find, > don't appear to protect usb_serial_disconnect > and serial_close from being called at the same time.
serial_close is safe because serial_disconnect lowers the refcount by one. usb_serial_probe() and usb_serial_open() both increment the refcount; the former implicitly.
> May be the protection is at a higher level? > Personally I don't beleive it. > If you know how this thing is supposed to work, > please, tell me.
The data structure to protect is serial_table. Everything else is protected by refcounts. Therefore the interesting race is between open and disconnect. Open is called with BKL (fs/char_dev.c::chrdev_open)
Now, regarding disconnect. It used to be called with BKL held. I haven't been able to verify that this is still the case. If not, then there's a race.
In addition usb_serial_probe() uses get_free_serial() early in the process before the device is ready. Without BKL, this too, races with open.
People, do we take BKL in khubd?
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