Re: [PATCH] usbnet: Fix two races between usbnet_stop() and the BH

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

On Mon, 24 Aug 2015, David Miller wrote:

quoted

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.