net: ena: fix theoretical Rx hang on low memory systems

[karo-tx-linux.git] / drivers / net / ethernet / amazon / ena / ena_netdev.c

diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index 4e9fbddd3b47eec1049cb2d653017b3f44b1b7e3..3c366bfbbab13db6a902f0f775cba94f114501c7 100644 (file)
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -190,6 +190,7 @@ static void ena_init_io_rings(struct ena_adapter *adapter)
                rxr->sgl_size = adapter->max_rx_sgl_size;
                rxr->smoothed_interval =
                        ena_com_get_nonadaptive_moderation_interval_rx(ena_dev);
+               rxr->empty_rx_queue = 0;
        }
 }
 
@@ -2619,6 +2620,58 @@ static void check_for_missing_tx_completions(struct ena_adapter *adapter)
        adapter->last_monitored_tx_qid = i % adapter->num_queues;
 }
 
+/* trigger napi schedule after 2 consecutive detections */
+#define EMPTY_RX_REFILL 2
+/* For the rare case where the device runs out of Rx descriptors and the
+ * napi handler failed to refill new Rx descriptors (due to a lack of memory
+ * for example).
+ * This case will lead to a deadlock:
+ * The device won't send interrupts since all the new Rx packets will be dropped
+ * The napi handler won't allocate new Rx descriptors so the device will be
+ * able to send new packets.
+ *
+ * This scenario can happen when the kernel's vm.min_free_kbytes is too small.
+ * It is recommended to have at least 512MB, with a minimum of 128MB for
+ * constrained environment).
+ *
+ * When such a situation is detected - Reschedule napi
+ */
+static void check_for_empty_rx_ring(struct ena_adapter *adapter)
+{
+       struct ena_ring *rx_ring;
+       int i, refill_required;
+
+       if (!test_bit(ENA_FLAG_DEV_UP, &adapter->flags))
+               return;
+
+       if (test_bit(ENA_FLAG_TRIGGER_RESET, &adapter->flags))
+               return;
+
+       for (i = 0; i < adapter->num_queues; i++) {
+               rx_ring = &adapter->rx_ring[i];
+
+               refill_required =
+                       ena_com_sq_empty_space(rx_ring->ena_com_io_sq);
+               if (unlikely(refill_required == (rx_ring->ring_size - 1))) {
+                       rx_ring->empty_rx_queue++;
+
+                       if (rx_ring->empty_rx_queue >= EMPTY_RX_REFILL) {
+                               u64_stats_update_begin(&rx_ring->syncp);
+                               rx_ring->rx_stats.empty_rx_ring++;
+                               u64_stats_update_end(&rx_ring->syncp);
+
+                               netif_err(adapter, drv, adapter->netdev,
+                                         "trigger refill for ring %d\n", i);
+
+                               napi_schedule(rx_ring->napi);
+                               rx_ring->empty_rx_queue = 0;
+                       }
+               } else {
+                       rx_ring->empty_rx_queue = 0;
+               }
+       }
+}
+
 /* Check for keep alive expiration */
 static void check_for_missing_keep_alive(struct ena_adapter *adapter)
 {
@@ -2673,6 +2726,8 @@ static void ena_timer_service(unsigned long data)
 
        check_for_missing_tx_completions(adapter);
 
+       check_for_empty_rx_ring(adapter);
+
        if (debug_area)
                ena_dump_stats_to_buf(adapter, debug_area);