Correct intercept queue handling of the overflow queue

The intercept queue was processing all the packets on the proxy queue.
This could result in the rewrite of more than one packet being put on
the overflow queue. If there are a lot of packets on the intercept
queue this could result in the overflow queue having more packets than
the size of the hardware queue. The code to submit the overflow queue
fails if it is unable to put all the packets of the overflow on the
hardware queue. This resulted in an infinite loop. It also resulted in
an assert being reported that packets are being added to the overflow
queue when it is not empty.

Correct this by checking if the overflow queue is non-empty after
rewriting each packet. If it is non-empty then stop processing
additional packets. The additional packets will be processed when the
barrier packet added to the hardware queue is executed due to its asyn
handler. This barrier packet is added to the hardware queue whenever
packets are saved on the overflow queue.

Change-Id: I2537911d3c3ba1aac61a0a35f1ab97426a66b5a2

runtime/hsa-runtime/core/runtime/intercept_queue.cpp

@@ -226,8 +226,8 @@ void InterceptQueue::StoreRelaxed(hsa_signal_value_t value) {
 
   // Loop over valid packets and process.
   uint64_t end = LoadWriteIndexAcquire();
-  uint64_t i;
-  for (i = next_packet_; i < end; i++) {
+  uint64_t i = next_packet_;
+  while (i < end) {
     if (!ring[i & mask].IsValid()) break;
 
     // Process callbacks.
@@ -238,6 +238,17 @@ void InterceptQueue::StoreRelaxed(hsa_signal_value_t value) {
 
     // Invalidate consumed packet
     atomic::Store(&ring[i & mask].dispatch.header, kInvalidHeader, std::memory_order_release);
+
+    // Packet has now been processed so advance the read index.
+    ++i;
+
+    // Only allow the rewrite of one packet to be on the overflow queue. When
+    // packets are put on the overflow queue a barrier packet will also be
+    // added which has an async handler that will ring the doorbell, That
+    // doorbell ring will ensure this function is re-invoked to put the
+    // overflow packets on the hardware queue and continue rewriting packets on
+    // the intercept queue.
+    if (!overflow_.empty()) break;
   }
 
   next_packet_ = i;