Don't assume EventPageMdl has been allocated...

...when calling EvtchnFifoContract()

The allocation is deferred until at least one event channel is allocated,
but EvtchnFifoContract() is called from EvtchnFifoRelease()n which can be
called before that happens.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>

diff --git a/src/xenbus/evtchn_fifo.c b/src/xenbus/evtchn_fifo.c
index c0456e0572f3870bf772fb4c6010ea44fcc4c86f..b8be93b68688be3e6593ec2950e5ab645bbb5142 100644 (file)
--- a/src/xenbus/evtchn_fifo.c
+++ b/src/xenbus/evtchn_fifo.c
@@ -272,7 +272,8 @@ EvtchnFifoContract(
         __FreePage(Mdl);
     }
 
-    __EvtchnFifoFree(Context->EventPageMdl);
+    if (Context->EventPageMdl != NULL)
+        __EvtchnFifoFree(Context->EventPageMdl);
 
     Context->EventPageMdl = NULL;
     Context->EventPageCount = 0;