Changeset 29910 in vbox

Timestamp:

May 31, 2010 2:04:26 PM (15 years ago)

Author:

vboxsync

Message:

PDMR3QueueFlushAll: Fixed race where we could leave unflushed items if an insert was completed right before clearing the active bit. Probably would require us to be preempted after the loop test for it to hit.

File:

• trunk/src/VBox/VMM/PDMQueue.cpp (modified) (2 diffs)

trunk/src/VBox/VMM/PDMQueue.cpp

@@ -671 +671 @@
      * flush are caught using the pending bit.
      *
-     * Note! The order in which the FF and pending bit are set and cleared is
-     *       important.
+     * Note! We must check the force action and pending flags after clearing
+     *       the active bit!
      */
     VM_FF_CLEAR(pVM, VM_FF_PDM_QUEUES);
-    if (!ASMAtomicBitTestAndSet(&pVM->pdm.s.fQueueFlushing, PDM_QUEUE_FLUSH_FLAG_ACTIVE_BIT))
+    while (!ASMAtomicBitTestAndSet(&pVM->pdm.s.fQueueFlushing, PDM_QUEUE_FLUSH_FLAG_ACTIVE_BIT))
     {
         ASMAtomicBitClear(&pVM->pdm.s.fQueueFlushing, PDM_QUEUE_FLUSH_FLAG_PENDING_BIT);
-        do
-        {
-            VM_FF_CLEAR(pVM, VM_FF_PDM_QUEUES);
-            for (PPDMQUEUE pCur = pVM->pUVM->pdm.s.pQueuesForced; pCur; pCur = pCur->pNext)
-                if (    pCur->pPendingR3
-                    ||  pCur->pPendingR0
-                    ||  pCur->pPendingRC)
-                    pdmR3QueueFlush(pCur);
-        } while (   ASMAtomicBitTestAndClear(&pVM->pdm.s.fQueueFlushing, PDM_QUEUE_FLUSH_FLAG_PENDING_BIT)
-                 || VM_FF_ISPENDING(pVM, VM_FF_PDM_QUEUES));
+
+        for (PPDMQUEUE pCur = pVM->pUVM->pdm.s.pQueuesForced; pCur; pCur = pCur->pNext)
+            if (    pCur->pPendingR3
+                ||  pCur->pPendingR0
+                ||  pCur->pPendingRC)
+                pdmR3QueueFlush(pCur);
 
         ASMAtomicBitClear(&pVM->pdm.s.fQueueFlushing, PDM_QUEUE_FLUSH_FLAG_ACTIVE_BIT);
+
+        /* We're done if there were no inserts while we were busy. */
+        if (   !ASMBitTest(&pVM->pdm.s.fQueueFlushing, PDM_QUEUE_FLUSH_FLAG_PENDING_BIT)
+            && !VM_FF_ISPENDING(pVM, VM_FF_PDM_QUEUES))
+            break;
+        VM_FF_CLEAR(pVM, VM_FF_PDM_QUEUES);
     }
 }
@@ -708 +710 @@
      * Get the lists.
      */
-    PPDMQUEUEITEMCORE pItems = (PPDMQUEUEITEMCORE)ASMAtomicXchgPtr((void * volatile *)&pQueue->pPendingR3, NULL);
+    PPDMQUEUEITEMCORE pItems   = (PPDMQUEUEITEMCORE)ASMAtomicXchgPtr((void * volatile *)&pQueue->pPendingR3, NULL);
     RTRCPTR           pItemsRC = ASMAtomicXchgRCPtr(&pQueue->pPendingRC, NIL_RTRCPTR);
     RTR0PTR           pItemsR0 = ASMAtomicXchgR0Ptr(&pQueue->pPendingR0, NIL_RTR0PTR);