[ 3.5.y.z extended stable ] Patch "xen-gnt: prevent adding duplicate gnt callbacks" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Fri Sep 20 19:32:28 UTC 2013

This is a note to let you know that I have just added a patch titled

    xen-gnt: prevent adding duplicate gnt callbacks

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 1218942cae47c07a5b2589e599e3880e55d779d1 Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <roger.pau at citrix.com>
Date: Wed, 31 Jul 2013 17:00:42 +0200
Subject: [PATCH] xen-gnt: prevent adding duplicate gnt callbacks
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 5f338d9001094a56cf87bd8a280b4e7ff953bb59 upstream.

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 at citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Cc: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Acked-by: Matt Wilson <msw at amazon.com>
Reviewed-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 drivers/xen/grant-table.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 22be735..8a6ecc5 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -728,9 +728,18 @@ void gnttab_request_free_callback(struct gnttab_free_callback *callback,
 				  void (*fn)(void *), void *arg, u16 count)
 	unsigned long flags;
+	struct gnttab_free_callback *cb;
 	spin_lock_irqsave(&gnttab_list_lock, flags);
-	if (callback->next)
-		goto out;
+	/* Check if the callback is already on the list */
+	cb = gnttab_free_callback_list;
+	while (cb) {
+		if (cb == callback)
+			goto out;
+		cb = cb->next;
+	}
 	callback->fn = fn;
 	callback->arg = arg;
 	callback->count = count;

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