[win-pv-devel] [PATCH 3/3] Make transmitter robust against a possible completion race

[Paul Durrant <pdurrant@xxxxxxxxx>]

It's possible that a transmission invoked on one CPU may complete on another
before the transmission invocation as finished. Therefore, once we have queued
a NET_BUFFER for transmission we should not use it's metadata again (including
the 'next' pointer).

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 src/xennet/receiver.c    | 2 ++
 src/xennet/transmitter.c | 5 +++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/xennet/receiver.c b/src/xennet/receiver.c
index 08c6413..863dbd7 100644
--- a/src/xennet/receiver.c
+++ b/src/xennet/receiver.c
@@ -89,6 +89,8 @@ __ReceiverAllocateNetBufferList(
         NET_BUFFER_DATA_OFFSET(NetBuffer) = Offset;
         NET_BUFFER_DATA_LENGTH(NetBuffer) = Length;
         NET_BUFFER_CURRENT_MDL_OFFSET(NetBuffer) = Offset;
+
+        ASSERT3P(NET_BUFFER_NEXT_NB(NetBuffer), ==, NULL);
     } else {
         NetBufferList = 
NdisAllocateNetBufferAndNetBufferList(Receiver->NetBufferListPool,
                                                               0,
diff --git a/src/xennet/transmitter.c b/src/xennet/transmitter.c
index b5e110a..91ed5f2 100644
--- a/src/xennet/transmitter.c
+++ b/src/xennet/transmitter.c
@@ -250,11 +250,12 @@ TransmitterSendNetBufferLists(
 
         NetBuffer = NET_BUFFER_LIST_FIRST_NB(NetBufferList);
         while (NetBuffer != NULL) {
+            PNET_BUFFER         NetBufferListNext = 
NET_BUFFER_NEXT_NB(NetBuffer);
             PVOID               Cookie = NetBufferList;
             XENVIF_PACKET_HASH  Hash;
             NTSTATUS            status;
 
-            ListReserved->Reference++;
+            InterlockedIncrement(&ListReserved->Reference);
 
             Hash.Algorithm = XENVIF_PACKET_HASH_ALGORITHM_NONE;
 
@@ -274,7 +275,7 @@ TransmitterSendNetBufferLists(
                 break;
             }
 
-            NetBuffer = NET_BUFFER_NEXT_NB(NetBuffer);
+            NetBuffer = NetBufferListNext;
         }
 
         NetBufferList = ListNext;
-- 
2.1.1


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