[PATCH 1/6] In some cases, the frontend may stop processing Tx ring requests in a timely manner. If this happens at the same time as ring disable, then the Tx code could spin forever at dispatch IRQL.

[Martin Harvey <Martin.Harvey@xxxxxxxxxx>]

This patch introduces a hard limit on how long the code will spin,
allowing a device disable or power transition to complete, albeit
at the cost of Tx requests being dropped or the ring being in
an indeterminate state. This has normally been seen at guest shutdown
where final ring state is of little consequence.

Signed-off-by: Martin Harvey <martin.harvey@xxxxxxxxxx>
---
 src/xenvif/transmitter.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/xenvif/transmitter.c b/src/xenvif/transmitter.c
index f6935a6..e114061 100644
--- a/src/xenvif/transmitter.c
+++ b/src/xenvif/transmitter.c
@@ -3933,6 +3933,8 @@ __TransmitterRingDisable(
     XenbusState                     State;
     ULONG                           Attempt;
     NTSTATUS                        status;
+    BOOLEAN                         ToProcess;
+    BOOLEAN                         Abort;
 
     Transmitter = Ring->Transmitter;
     Frontend = Transmitter->Frontend;
@@ -3985,24 +3987,31 @@ __TransmitterRingDisable(
     }
 
     Attempt = 0;
+    ToProcess = Ring->ResponsesProcessed != Ring->RequestsPushed;
+    Abort = ((Attempt >= 100) || (State != XenbusStateConnected));
+
     ASSERT3U(Ring->RequestsPushed, ==, Ring->RequestsPosted);
-    while (Ring->ResponsesProcessed != Ring->RequestsPushed) {
+    while (ToProcess && !Abort) {
         Attempt++;
-        ASSERT(Attempt < 100);
+
+        KeStallExecutionProcessor(1000);    // 1ms
 
         // Try to move things along
         __TransmitterRingSend(Ring);
         (VOID) TransmitterRingPoll(Ring);
 
-        if (State != XenbusStateConnected)
-            __TransmitterRingFakeResponses(Ring);
-
         // We are waiting for a watch event at DISPATCH_LEVEL so
         // it is our responsibility to poll the store ring.
         XENBUS_STORE(Poll,
                      &Transmitter->StoreInterface);
 
-        KeStallExecutionProcessor(1000);    // 1ms
+        ToProcess = Ring->ResponsesProcessed != Ring->RequestsPushed;
+        Abort = ((Attempt >= 100) || (State != XenbusStateConnected));
+    }
+    if (Abort)
+    {
+        __TransmitterRingFakeResponses(Ring);
+        (VOID) TransmitterRingPoll(Ring);
     }
 
     Ring->Enabled = FALSE;
-- 
2.25.0.windows.1