netdev - Re: [PATCH] usbnet: Fix two races between usbnet

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Message-Id: <20150824.113538.2034261393606624731.davem@davemloft.net>
Date:	Mon, 24 Aug 2015 11:35:38 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	stern@...land.harvard.edu
Cc:	eugene.shatokhin@...alab.ru, bjorn@...k.no, oneukum@...e.com,
	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

From: Alan Stern <stern@...land.harvard.edu>
Date: Mon, 24 Aug 2015 14:06:15 -0400 (EDT)

> On Mon, 24 Aug 2015, David Miller wrote:
>> Atomic operations like clear_bit also will behave that way.
> 
> Are you certain about that?  I couldn't find any mention of it in
> Documentation/atomic_ops.txt.
> 
> 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.

Indeed, we do have platforms like 32-bit sparc and parisc that do this.

So, taking that into consideration, this is a bit unfortunate and on
such platforms we do have this problem.
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