[PATCH 3.16 312/410] xen/pirq: fix error path cleanup when binding MSIs

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Roger Pau Monne <roger.pau@xxxxxxxxxx>

commit 910f8befdf5bccf25287d9f1743e3e546bcb7ce0 upstream.

Current cleanup in the error path of xen_bind_pirq_msi_to_irq is
wrong. First of all there's an off-by-one in the cleanup loop, which
can lead to unbinding wrong IRQs.

Secondly IRQs not bound won't be freed, thus leaking IRQ numbers.

Note that there's no need to differentiate between bound and unbound
IRQs when freeing them, __unbind_from_irq will deal with both of them
correctly.

Fixes: 4892c9b4ada9f9 ("xen: add support for MSI message groups")
Reported-by: Hooman Mirhadi <mirhadih@xxxxxxxxxx>
Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Reviewed-by: Amit Shah <aams@xxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/xen/events/events_base.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -763,8 +763,8 @@ out:
 	mutex_unlock(&irq_mapping_update_lock);
 	return irq;
 error_irq:
-	for (; i >= 0; i--)
-		__unbind_from_irq(irq + i);
+	while (nvec--)
+		__unbind_from_irq(irq + nvec);
 	mutex_unlock(&irq_mapping_update_lock);
 	return ret;
 }