linux-kernel - Re: [PATCH] usbnet: Fix two races between usbnet

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Message-ID: <1440506198.13824.5.camel@suse.com>
Date:	Tue, 25 Aug 2015 14:36:38 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	David Miller <davem@...emloft.net>, eugene.shatokhin@...alab.ru,
	bjorn@...k.no, netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usbnet: Fix two races between usbnet_stop() and the BH

On Mon, 2015-08-24 at 14:21 -0400, Alan Stern wrote:
> > In theory, an architecture could implement atomic bit operations
> using 
> > a spinlock to insure atomicity.  I don't know if any architectures
> do 
> > this, but if they do then the scenario above could arise.
> 
> Now that I see this in writing, I realize it's not possible after
> all.  
> clear_bit() et al. will work with a single unsigned long, which
> doesn't
> leave any place for spinlocks or other mechanisms.  I was thinking of 
> atomic_t.

Refuting yourself you are making the assumption that the lock has
to be inside the data structure. That is not true.

	Regards
		Oliver


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