[PATCH 3/3] Avoid requeuing QueueDpc during ring swizzles

[Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>]

If a ring is paused by xennet, __ReceiverRingSwizzle immediately queues
another QueueDpc. In low-resource conditions where NDIS is unable to
process traffic, this will cause an infinite cascade of DPCs and lock up
the system.

Stop doing that in __ReceiverRingSwizzle. Instead, requeue QueueDpc from
ReceiverReturnPacket after incrementing Receiver->Returned to reevaluate
the paused status. This ensures that incoming traffic storms can be
safely handled.

Signed-off-by: Tu Dinh <ngoc-tu.dinh@xxxxxxxxxx>
---
 src/xenvif/receiver.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/src/xenvif/receiver.c b/src/xenvif/receiver.c
index 29bd325..95a4f5c 100644
--- a/src/xenvif/receiver.c
+++ b/src/xenvif/receiver.c
@@ -1560,11 +1560,12 @@ __ReceiverRingSwizzle(
             Pause = FALSE;
     }
 
+    // If there will be no more returns then we can't pause either
+    if (Pause && Receiver->Loaned == Receiver->Returned)
+        Pause = FALSE;
+
     if (Pause) {
         Ring->Paused = TRUE;
-
-        if (KeInsertQueueDpc(&Ring->QueueDpc, NULL, NULL))
-            Ring->QueueDpcs++;
     } else {
         BOOLEAN Paused = Ring->Paused;
 
@@ -3796,6 +3797,9 @@ ReceiverReturnPacket(
 
     ASSERT3S(Loaned - Returned, >=, 0);
 
+    if (KeInsertQueueDpc(&Ring->QueueDpc, NULL, NULL))
+        Ring->QueueDpcs++;
+
     KeSetEvent(&Receiver->Event, 0, FALSE);
 }
 
-- 
2.54.0.windows.1



--
Ngoc Tu Dinh | Vates XCP-ng Developer

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