[PATCH net] gve: fix gve_get_stats()

[PATCH net] gve: fix gve_get_stats()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

gve_get_stats() can report wrong numbers if/when u64_stats_fetch_retry()
returns true.

What is needed here is to sample values in temporary variables,
and only use them after each loop is ended.

Fixes: f5cedc84a30d ("gve: Add transmit and receive support")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Catherine Sullivan <csully@google.com>
Cc: Sagi Shahar <sagis@google.com>
Cc: Jon Olson <jonolson@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Luigi Rizzo <lrizzo@google.com>
Cc: Jeroen de Borst <jeroendb@google.com>
Cc: Tao Liu <xliutaox@google.com>
---
 drivers/net/ethernet/google/gve/gve_main.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 099a2bc5ae6704553516561106a0bb6822fdb8e4..99837c9d2cba698ada900229330cb10bc1606a6b 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -41,6 +41,7 @@ static void gve_get_stats(struct net_device *dev, struct rtnl_link_stats64 *s)
 {
 	struct gve_priv *priv = netdev_priv(dev);
 	unsigned int start;
+	u64 packets, bytes;
 	int ring;
 
 	if (priv->rx) {
@@ -48,10 +49,12 @@ static void gve_get_stats(struct net_device *dev, struct rtnl_link_stats64 *s)
 			do {
 				start =
 				  u64_stats_fetch_begin(&priv->rx[ring].statss);
-				s->rx_packets += priv->rx[ring].rpackets;
-				s->rx_bytes += priv->rx[ring].rbytes;
+				packets = priv->rx[ring].rpackets;
+				bytes = priv->rx[ring].rbytes;
 			} while (u64_stats_fetch_retry(&priv->rx[ring].statss,
 						       start));
+			s->rx_packets += packets;
+			s->rx_bytes += bytes;
 		}
 	}
 	if (priv->tx) {
@@ -59,10 +62,12 @@ static void gve_get_stats(struct net_device *dev, struct rtnl_link_stats64 *s)
 			do {
 				start =
 				  u64_stats_fetch_begin(&priv->tx[ring].statss);
-				s->tx_packets += priv->tx[ring].pkt_done;
-				s->tx_bytes += priv->tx[ring].bytes_done;
+				packets = priv->tx[ring].pkt_done;
+				bytes = priv->tx[ring].bytes_done;
 			} while (u64_stats_fetch_retry(&priv->tx[ring].statss,
 						       start));
+			s->tx_packets += packets;
+			s->tx_bytes += bytes;
 		}
 	}
 }
-- 
2.33.0.800.g4c38ced690-goog

Re: [PATCH net] gve: fix gve_get_stats()

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue,  5 Oct 2021 17:30:30 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> gve_get_stats() can report wrong numbers if/when u64_stats_fetch_retry()
> returns true.
> 
> What is needed here is to sample values in temporary variables,
> and only use them after each loop is ended.
> 
> [...]

Here is the summary with links:
  - [net] gve: fix gve_get_stats()
    https://git.kernel.org/netdev/net/c/2f57d4975fa0

You are awesome, thank you!
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