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Subject[PATCH 06/93] xen-gnt: prevent adding duplicate gnt callbacks
Date -stable review patch.  If anyone has any objections, please let me know.


From: Roger Pau Monne <>

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 <>
Cc: Konrad Rzeszutek Wilk <>
Cc: David Vrabel <>
Signed-off-by: Konrad Rzeszutek Wilk <>
Acked-by: Matt Wilson <>
Reviewed-by: David Vrabel <>
Signed-off-by: Kamal Mostafa <>
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 157c0cc..51be226 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -729,9 +729,18 @@ 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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