From 5f338d9001094a56cf87bd8a280b4e7ff953bb59 Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <roger.pau@citrix.com>
Date: Wed, 31 Jul 2013 17:00:42 +0200
Subject: [PATCH] xen-gnt: prevent adding duplicate gnt callbacks
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With the current implementation, the callback in the tail of the list
can be added twice, because the check done in
gnttab_request_free_callback is bogus, callback->next can be NULL if
it is the last callback in the list. If we add the same callback twice
we end up with an infinite loop, were callback == callback->next.

Replace this check with a proper one that iterates over the list to
see if the callback has already been added.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Matt Wilson <msw@amazon.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
CC: stable@vger.kernel.org
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