NetKVM: Prevent hanging in SendControlMessage

Windows with NetKVM has a little chance hang during shutdown.

If the NetKVM has not initialized yet (or reset), QEMU will ignore
the control message. It will cause driver hanging in infinite while loop
for waiting response (which leads to windows hang in shutdown). In our
test, there is a little chance to receive an OID for setting multicast list
after device reset. To make symptom more clear, I have added some log.
Below is the log and call stack when this situation happens:

Logs:

[ParaNdis_OnShutdown]=>
Common [ParaNdis_ResetVirtIONetDevice] Done
[ParaNdis_OnOidSetMulticastList] Go
[ParaNdis_UpdateDeviceFilters] Do
[CParaNdisCX::SendControlMessage] enter: 4277 - cls: 0, cmd: 0
CParaNdisCX::SendControlMessage - ERROR: in while
Assertion: *** DPC watchdog timeout
    This is NOT a break in update time
    This is most likely a BUG in an ISR
    Perform a stack trace to find the culprit
    The period will be doubled on continuation
    Use gh to continue!!

Call stack:

kd> k
ChildEBP RetAddr
8b582530 83ab50be nt!KeAccumulateTicks+0x3c5
8b582570 83ab4f6b nt!KeUpdateRunTime+0x145
8b5825c8 83ab9c17 nt!KeUpdateSystemTime+0x613
8b5825c8 83a10122 nt!KeUpdateSystemTimeAssist+0x13
8b582680 8e16db70 hal!HalpTscStallExecutionProcessor+0xc0
WARNING: Stack unwind information not available. Following frames may be
wrong.
8b582700 8e16b216 netkvm+0x4b70
8b582730 8e16c418 netkvm+0x2216
8b582740 8e16f219 netkvm+0x3418
8b582750 8e17740f netkvm+0x6219
8b5827a8 880fc32b netkvm+0xe40f
8b5827f0 880a8ce3 ndis!ndisMDoOidRequest+0x3a1
8b582818 880a87ff ndis!ndisFQueueRequestOnNext+0x21e
8b582880 8df21086 ndis!NdisFOidRequest+0x181
8b5828a0 880fc961 pacer!PcFilterRequest+0x78
8b582900 880a8c5c ndis!ndisFDoOidRequest+0x1a2
8b582928 880a87ff ndis!ndisFQueueRequestOnNext+0x197
8b582990 8df15b22 ndis!NdisFOidRequest+0x181
8b5829b0 880fc961 wfplwf!FilterOidRequest+0x50
8b582a10 880a7799 ndis!ndisFDoOidRequest+0x1a2
8b582a3c 8810d602 ndis!ndisQueueRequestOnTop+0x224
8b582ab0 8810d686 ndis!ndisMOidRequest+0x1dd
8b582ac0 882a4646 ndis!NdisOidRequest+0xf
8b582b7c 88254d1d tcpip!FlpNdisRequestUnderReference+0x7d
8b582bb8 8825523b tcpip!FlpMulticastListSet+0xa1
8b582bc4 88251a2e tcpip!FlpSerializedNdisDeleteGroupWorker+0xd
8b582bec 83c4f460 tcpip!FlpSerializedNdisRequestWorkerRoutine+0x41
8b582c00 83ab7aab nt!IopProcessWorkItem+0x23
8b582c50 83c43f5e nt!ExpWorkerThread+0x10d
8b582c90 83aeb219 nt!PspSystemThreadStartup+0x9e
00000000 00000000 nt!KiThreadStartup+0x19

Signed-off-by: yuchenlin <yuchenlin@synology.com>

NetKVM/Common/ParaNdis-CX.cpp

@@ -102,17 +102,24 @@ BOOLEAN CParaNdisCX::SendControlMessage(
         if (0 <= m_VirtQueue.AddBuf(sg, nOut, 1, (PVOID)1, NULL, 0))
         {
             UINT len;
+            void *p;
             m_Context->m_CxStateMachine.RegisterOutstandingItem();
 
             m_VirtQueue.Kick();
-            while (!m_VirtQueue.GetBuf(&len))
+            p = m_VirtQueue.GetBuf(&len);
+            for (int i = 0; i < 1000 && !p; ++i)
             {
                 UINT interval = 1;
                 NdisStallExecution(interval);
+                p = m_VirtQueue.GetBuf(&len);
             }
             m_Context->m_CxStateMachine.UnregisterOutstandingItem();
 
-            if (len != sizeof(virtio_net_ctrl_ack))
+            if (!p)
+            {
+                DPrintf(0, "%s - ERROR: get_buf failed\n", __FUNCTION__);
+            }
+            else if (len != sizeof(virtio_net_ctrl_ack))
             {
                 DPrintf(0, "%s - ERROR: wrong len %d\n", __FUNCTION__, len);
             }