[PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet stalling

* [PATCH net] net: wireless: intel: iwlwifi: fix GRO_NORMAL packet stalling
@ 2019-11-27  9:41 Alexander Lobakin
  2019-11-27  9:58 ` Luciano Coelho
                   ` (2 more replies)
  0 siblings, 3 replies; 11+ messages in thread
From: Alexander Lobakin @ 2019-11-27  9:41 UTC (permalink / raw)
  To: David S. Miller
  Cc: Edward Cree, Jiri Pirko, Eric Dumazet, Ido Schimmel, Paolo Abeni,
	Petr Machata, Sabrina Dubroca, Florian Fainelli, Jassi Brar,
	Manish Chopra, GR-Linux-NIC-Dev, Johannes Berg,
	Emmanuel Grumbach, Luca Coelho, Intel Linux Wireless, Kalle Valo,
	Nicholas Johnson, Kenneth R. Crudup, Alexander Lobakin, netdev,
	linux-wireless, linux-kernel

Commit 6570bc79c0df ("net: core: use listified Rx for GRO_NORMAL in
napi_gro_receive()") has applied batched GRO_NORMAL packets processing
to all napi_gro_receive() users, including mac80211-based drivers.

However, this change has led to a regression in iwlwifi driver [1][2] as
it is required for NAPI users to call napi_complete_done() or
napi_complete() and the end of every polling iteration, whilst iwlwifi
doesn't use NAPI scheduling at all and just calls napi_gro_flush().
In that particular case, packets which have not been already flushed
from napi->rx_list stall in it until at least next Rx cycle.

Fix this by adding a manual flushing of the list to iwlwifi driver right
before napi_gro_flush() call to mimic napi_complete() logics.

I prefer to open-code gro_normal_list() rather than exporting it for 2
reasons:
* to prevent from using it and napi_gro_flush() in any new drivers,
  as it is the *really* bad way to use NAPI that should be avoided;
* to keep gro_normal_list() static and don't lose any CC optimizations.

I also don't add the "Fixes:" tag as the mentioned commit was only a
trigger that only exposed an improper usage of NAPI in this particular
driver.

[1] https://lore.kernel.org/netdev/PSXP216MB04388962C411CD0B17A86F47804A0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COM
[2] https://bugzilla.kernel.org/show_bug.cgi?id=205647

Signed-off-by: Alexander Lobakin <alobakin@dlink.ru>
---
 drivers/net/wireless/intel/iwlwifi/pcie/rx.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
index a4d325fcf94a..452da44a21e0 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
@@ -1421,6 +1421,7 @@ static struct iwl_rx_mem_buffer *iwl_pcie_get_rxb(struct iwl_trans *trans,
 static void iwl_pcie_rx_handle(struct iwl_trans *trans, int queue)
 {
 	struct iwl_trans_pcie *trans_pcie = IWL_TRANS_GET_PCIE_TRANS(trans);
+	struct napi_struct *napi;
 	struct iwl_rxq *rxq;
 	u32 r, i, count = 0;
 	bool emergency = false;
@@ -1526,8 +1527,16 @@ static void iwl_pcie_rx_handle(struct iwl_trans *trans, int queue)
 	if (unlikely(emergency && count))
 		iwl_pcie_rxq_alloc_rbs(trans, GFP_ATOMIC, rxq);
 
-	if (rxq->napi.poll)
-		napi_gro_flush(&rxq->napi, false);
+	napi = &rxq->napi;
+	if (napi->poll) {
+		if (napi->rx_count) {
+			netif_receive_skb_list(&napi->rx_list);
+			INIT_LIST_HEAD(&napi->rx_list);
+			napi->rx_count = 0;
+		}
+
+		napi_gro_flush(napi, false);
+	}
 
 	iwl_pcie_rxq_restock(trans, rxq);
 }
-- 
2.24.0


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