linux-kernel - Re: [PATCH] USB: add USB test and measurement class driver

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Message-ID: <Pine.LNX.4.44L0.0808271203150.2498-100000@iolanthe.rowland.org>
Date:	Wed, 27 Aug 2008 12:06:23 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Greg KH <greg@...ah.com>, <linux-usb@...r.kernel.org>,
	Stefan Kopp <stefan_kopp@...lent.com>,
	Marcel Janssen <korgull@...e.nl>,
	Felipe Balbi <me@...ipebalbi.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: add USB test and measurement class driver

On Wed, 27 Aug 2008, Oliver Neukum wrote:

> This is a race condition.
> 
> CPU A					CPU B
> open()
> usb_find_interface()
> 						disconnect()
> 						kref_put()
> 						usbtmc_delete()
> 						kfree()
> kref_get()
> 
> You can write to free memory. You must use a static mutex for
> mutual exclusion between open() and disconnect()

Is that necessary?  usbcore includes its own mutual exclusion now.  
Look in file.c at how minor_rwsem is used.

Alan Stern

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