From: Tim Sell <timothy.s...@unisys.com>

Prevent faults processing messages for devices that no driver has yet
registered to handle.

Previously, code of the form:

    drv = to_visor_driver(dev->device.driver);
    if (!drv)
        goto away;

was not having the desired intent, because to_visor_driver() was
essentially returning garbage if its argument was NULL.  The only existing
case of this is in initiate_chipset_device_pause_resume(), which is called
during IOVM service partition recovery.  We were thus faulting when IOVM
service partition recovery was initiated on a bus that had at least one
device for which no function driver had registered
(visorbus_register_visor_driver).

Signed-off-by: Tim Sell <timothy.s...@unisys.com>
Signed-off-by: Benjamin Romer <benjamin.ro...@unisys.com>
---
 drivers/staging/unisys/include/visorbus.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/unisys/include/visorbus.h 
b/drivers/staging/unisys/include/visorbus.h
index e4a21e4..a0144c6 100644
--- a/drivers/staging/unisys/include/visorbus.h
+++ b/drivers/staging/unisys/include/visorbus.h
@@ -113,7 +113,8 @@ struct visor_driver {
        struct driver_attribute version_attr;
 };
 
-#define to_visor_driver(x) container_of(x, struct visor_driver, driver)
+#define to_visor_driver(x) ((x) ? \
+       (container_of(x, struct visor_driver, driver)) : (NULL))
 
 /** A device type for things "plugged" into the visorbus bus */
 
-- 
2.1.4

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