From: Oliver Neukum <oliver@neukum.org>
To: Jiri Kosina <jkosina@suse.cz>
Subject: Re: Use of usb_find_interface in open is racy
Date: Wed, 18 Nov 2009 15:27:18 +0100
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Cc: Russ Dill <russ.dill@gmail.com>, linux-kernel@vger.kernel.org,
       linux-usb@vger.kernel.org
References: <f9d2a5e10911171306r416eaf2k45c3256370e82eda@mail.gmail.com> <alpine.LRH.2.00.0911181141030.31913@twin.jikos.cz>
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Am Mittwoch, 18. November 2009 11:41:25 schrieb Jiri Kosina:
> > User space receives the hotplug event for the class device, makes the
> > device node and notifies another program that opens the device node.
> > The program opens the device node which calls into usb_open and then
> > skel_open. skel_open calls usb_find_interface. usb_find_interfaces
> > searches the klist_devices of skel_driver, finds no device associated
> > with the minor number and returns NULL. skel_open returns -ENODEV.
> > 
> > Control returns to really_probe and really_probe calls driver_bound
> > which adds the device to the list of devices associated with
> > skel_driver (klist_devices).
> > 
> > I'm not sure what the right way to solve this is. A call to
> > wait_for_device_probe() in the skel_open call before calling
> > usb_find_interface fixes the problem, but it is a rather large hammer.
> 

Device core code is hard to follow, but I tried.
How about simply covering all of usb_register_dev() with minor_rwsem?

	Regards
		Oliver
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