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Subject[PATCH 5.4 023/104] net: Fix packet reordering caused by GRO and listified RX cooperation
Date
From: Maxim Mikityanskiy <maximmi@mellanox.com>

[ Upstream commit c80794323e82ac6ab45052ebba5757ce47b4b588 ]

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>
Acked-by: Alexander Lobakin <alobakin@dlink.ru>
Acked-by: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/wireless/intel/iwlwifi/pcie/rx.c | 4 -
net/core/dev.c | 64 +++++++++++++--------------
2 files changed, 35 insertions(+), 33 deletions(-)

--- a/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/rx.c
@@ -1537,13 +1537,13 @@ out:

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);
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5270,9 +5270,29 @@ 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;
@@ -5305,7 +5325,8 @@ static int napi_gro_complete(struct sk_b
}

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,
@@ -5318,7 +5339,7 @@ static void __napi_gro_flush_chain(struc
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--;
}

@@ -5421,7 +5442,7 @@ static void gro_pull_from_frag0(struct s
}
}

-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;

@@ -5437,7 +5458,7 @@ static void gro_flush_oldest(struct list
* 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 *,
@@ -5513,7 +5534,7 @@ static enum gro_result dev_gro_receive(s

if (pp) {
skb_list_del_init(pp);
- napi_gro_complete(pp);
+ napi_gro_complete(napi, pp);
napi->gro_hash[hash].count--;
}

@@ -5524,7 +5545,7 @@ static enum gro_result dev_gro_receive(s
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++;
}
@@ -5672,26 +5693,6 @@ struct sk_buff *napi_get_frags(struct na
}
EXPORT_SYMBOL(napi_get_frags);

-/* 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 gro_result_t napi_frags_finish(struct napi_struct *napi,
struct sk_buff *skb,
gro_result_t ret)
@@ -5979,8 +5980,6 @@ bool napi_complete_done(struct napi_stru
NAPIF_STATE_IN_BUSY_POLL)))
return false;

- gro_normal_list(n);
-
if (n->gro_bitmask) {
unsigned long timeout = 0;

@@ -5996,6 +5995,9 @@ bool napi_complete_done(struct napi_stru
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);
@@ -6327,8 +6329,6 @@ static int napi_poll(struct napi_struct
goto out_unlock;
}

- gro_normal_list(n);
-
if (n->gro_bitmask) {
/* flush too old packets
* If HZ < 1000, flush all packets.
@@ -6336,6 +6336,8 @@ static int napi_poll(struct napi_struct
napi_gro_flush(n, HZ >= 1000);
}

+ gro_normal_list(n);
+
/* Some drivers may have called napi_schedule
* prior to exhausting their budget.
*/

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