netdev - [PATCH net-next 04/10] net: enetc: stop XDP NAPI processing when build

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Date:   Sat, 17 Apr 2021 00:22:19 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Po Liu <po.liu@....com>
Cc:     Claudiu Manoil <claudiu.manoil@....com>,
        Alex Marginean <alexandru.marginean@....com>,
        Yangbo Lu <yangbo.lu@....com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: [PATCH net-next 04/10] net: enetc: stop XDP NAPI processing when build_skb() fails

From: Vladimir Oltean <vladimir.oltean@....com>

When the code path below fails:

enetc_clean_rx_ring_xdp // XDP_PASS
-> enetc_build_skb
   -> enetc_map_rx_buff_to_skb
      -> build_skb

enetc_clean_rx_ring_xdp will 'break', but that 'break' instruction isn't
strong enough to actually break the NAPI poll loop, just the switch/case
statement for XDP actions. So we increment rx_frm_cnt and go to the next
frames minding our own business.

Instead let's do what the skb NAPI poll function does, and break the
loop now, waiting for the memory pressure to go away. Otherwise the next
calls to build_skb() are likely to fail too.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index c6f984473337..469170076efa 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -1275,8 +1275,7 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
 					      &i, &cleaned_cnt,
 					      ENETC_RXB_DMA_SIZE_XDP);
 			if (unlikely(!skb))
-				/* Exit the switch/case, not the loop */
-				break;
+				goto out;
 
 			napi_gro_receive(napi, skb);
 			break;
@@ -1338,6 +1337,7 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
 		rx_frm_cnt++;
 	}
 
+out:
 	rx_ring->next_to_clean = i;
 
 	rx_ring->stats.packets += rx_frm_cnt;
-- 
2.25.1