[PATCH net v2] net: Fix packet reordering caused by GRO and listified RX cooperation

[Maxim Mikityanskiy <maximmi@mellanox.com>]

Commit 323ebb61e32b ("net: use listified RX for handling GRO_NORMAL
skbs") introduces batching of GRO_NORMAL packets in napi_frags_finish,
and commit 6570bc79c0df ("net: core: use listified Rx for GRO_NORMAL in
napi_gro_receive()") adds the same to napi_skb_finish. However,
dev_gro_receive (that is called just before napi_{frags,skb}_finish) can
also pass skbs to the networking stack: e.g., when the GRO session is
flushed, napi_gro_complete is called, which passes pp directly to
netif_receive_skb_internal, skipping napi->rx_list. It means that the
packet stored in pp will be handled by the stack earlier than the
packets that arrived before, but are still waiting in napi->rx_list. It
leads to TCP reorderings that can be observed in the TCPOFOQueue counter
in netstat.

This commit fixes the reordering issue by making napi_gro_complete also
use napi->rx_list, so that all packets going through GRO will keep their
order. In order to keep napi_gro_flush working properly, gro_normal_list
calls are moved after the flush to clear napi->rx_list.

iwlwifi calls napi_gro_flush directly and does the same thing that is
done by gro_normal_list, so the same change is applied there:
napi_gro_flush is moved to be before the flush of napi->rx_list.

A few other drivers also use napi_gro_flush (brocade/bna/bnad.c,
cortina/gemini.c, hisilicon/hns3/hns3_enet.c). The first two also use
napi_complete_done afterwards, which performs the gro_normal_list flush,
so they are fine. The latter calls napi_gro_receive right after
napi_gro_flush, so it can end up with non-empty napi->rx_list anyway.

Fixes: 323ebb61e32b ("net: use listified RX for handling GRO_NORMAL skbs")
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Cc: Alexander Lobakin <alobakin@dlink.ru>
Cc: Edward Cree <ecree@solarflare.com>
---
v2 changes:

Flush napi->rx_list after napi_gro_flush, not before. Do it in iwlwifi
as well.

Please also pay attention that there is gro_flush_oldest that also calls
napi_gro_complete and DOESN'T do gro_normal_list to flush napi->rx_list.
I guess, it's not required in this flow, but if I'm wrong, please tell
me.

 drivers/net/wireless/intel/iwlwifi/pcie/rx.c |  4 +-
 net/core/dev.c                               | 64 ++++++++++----------
 2 files changed, 35 insertions(+), 33 deletions(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
index 452da44a21e0..f0b8ff67a1bc 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
@@ -1529,13 +1529,13 @@ static void iwl_pcie_rx_handle(struct iwl_trans *trans, int queue)
 
 	napi = &rxq->napi;
 	if (napi->poll) {
+		napi_gro_flush(napi, false);
+
 		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);
diff --git a/net/core/dev.c b/net/core/dev.c
index e82e9b82dfd9..cca03914108a 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5491,9 +5491,29 @@ static void flush_all_backlogs(void)
 	put_online_cpus();
 }
 
+/* Pass the currently batched GRO_NORMAL SKBs up to the stack. */
+static void gro_normal_list(struct napi_struct *napi)
+{
+	if (!napi->rx_count)
+		return;
+	netif_receive_skb_list_internal(&napi->rx_list);
+	INIT_LIST_HEAD(&napi->rx_list);
+	napi->rx_count = 0;
+}
+
+/* Queue one GRO_NORMAL SKB up for list processing. If batch size exceeded,
+ * pass the whole batch up to the stack.
+ */
+static void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb)
+{
+	list_add_tail(&skb->list, &napi->rx_list);
+	if (++napi->rx_count >= gro_normal_batch)
+		gro_normal_list(napi);
+}
+
 INDIRECT_CALLABLE_DECLARE(int inet_gro_complete(struct sk_buff *, int));
 INDIRECT_CALLABLE_DECLARE(int ipv6_gro_complete(struct sk_buff *, int));
-static int napi_gro_complete(struct sk_buff *skb)
+static int napi_gro_complete(struct napi_struct *napi, struct sk_buff *skb)
 {
 	struct packet_offload *ptype;
 	__be16 type = skb->protocol;
@@ -5526,7 +5546,8 @@ static int napi_gro_complete(struct sk_buff *skb)
 	}
 
 out:
-	return netif_receive_skb_internal(skb);
+	gro_normal_one(napi, skb);
+	return NET_RX_SUCCESS;
 }
 
 static void __napi_gro_flush_chain(struct napi_struct *napi, u32 index,
@@ -5539,7 +5560,7 @@ static void __napi_gro_flush_chain(struct napi_struct *napi, u32 index,
 		if (flush_old && NAPI_GRO_CB(skb)->age == jiffies)
 			return;
 		skb_list_del_init(skb);
-		napi_gro_complete(skb);
+		napi_gro_complete(napi, skb);
 		napi->gro_hash[index].count--;
 	}
 
@@ -5641,7 +5662,7 @@ static void gro_pull_from_frag0(struct sk_buff *skb, int grow)
 	}
 }
 
-static void gro_flush_oldest(struct list_head *head)
+static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
 {
 	struct sk_buff *oldest;
 
@@ -5657,7 +5678,7 @@ static void gro_flush_oldest(struct list_head *head)
 	 * SKB to the chain.
 	 */
 	skb_list_del_init(oldest);
-	napi_gro_complete(oldest);
+	napi_gro_complete(napi, oldest);
 }
 
 INDIRECT_CALLABLE_DECLARE(struct sk_buff *inet_gro_receive(struct list_head *,
@@ -5733,7 +5754,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 
 	if (pp) {
 		skb_list_del_init(pp);
-		napi_gro_complete(pp);
+		napi_gro_complete(napi, pp);
 		napi->gro_hash[hash].count--;
 	}
 
@@ -5744,7 +5765,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 		goto normal;
 
 	if (unlikely(napi->gro_hash[hash].count >= MAX_GRO_SKBS)) {
-		gro_flush_oldest(gro_head);
+		gro_flush_oldest(napi, gro_head);
 	} else {
 		napi->gro_hash[hash].count++;
 	}
@@ -5802,26 +5823,6 @@ struct packet_offload *gro_find_complete_by_type(__be16 type)
 }
 EXPORT_SYMBOL(gro_find_complete_by_type);
 
-/* Pass the currently batched GRO_NORMAL SKBs up to the stack. */
-static void gro_normal_list(struct napi_struct *napi)
-{
-	if (!napi->rx_count)
-		return;
-	netif_receive_skb_list_internal(&napi->rx_list);
-	INIT_LIST_HEAD(&napi->rx_list);
-	napi->rx_count = 0;
-}
-
-/* Queue one GRO_NORMAL SKB up for list processing. If batch size exceeded,
- * pass the whole batch up to the stack.
- */
-static void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb)
-{
-	list_add_tail(&skb->list, &napi->rx_list);
-	if (++napi->rx_count >= gro_normal_batch)
-		gro_normal_list(napi);
-}
-
 static void napi_skb_free_stolen_head(struct sk_buff *skb)
 {
 	skb_dst_drop(skb);
@@ -6200,8 +6201,6 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 				 NAPIF_STATE_IN_BUSY_POLL)))
 		return false;
 
-	gro_normal_list(n);
-
 	if (n->gro_bitmask) {
 		unsigned long timeout = 0;
 
@@ -6217,6 +6216,9 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 			hrtimer_start(&n->timer, ns_to_ktime(timeout),
 				      HRTIMER_MODE_REL_PINNED);
 	}
+
+	gro_normal_list(n);
+
 	if (unlikely(!list_empty(&n->poll_list))) {
 		/* If n->poll_list is not empty, we need to mask irqs */
 		local_irq_save(flags);
@@ -6548,8 +6550,6 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 		goto out_unlock;
 	}
 
-	gro_normal_list(n);
-
 	if (n->gro_bitmask) {
 		/* flush too old packets
 		 * If HZ < 1000, flush all packets.
@@ -6557,6 +6557,8 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 		napi_gro_flush(n, HZ >= 1000);
 	}
 
+	gro_normal_list(n);
+
 	/* Some drivers may have called napi_schedule
 	 * prior to exhausting their budget.
 	 */
-- 
2.20.1