net: mscc: ocelot: fix race between ndo_get_stats64 and ocelot_check_stats_work

The 2 methods can run concurrently, and one will change the window of
counters (SYS_STAT_CFG_STAT_VIEW) that the other sees. The fix is
similar to what commit 7fbf6795 ("net: mscc: ocelot: fix mutex lock
error during ethtool stats read") has done for ethtool -S.

Fixes: a556c76a ("net: mscc: Add initial Ocelot switch support")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mscc/ocelot_net.c

@@ -726,6 +726,8 @@ static void ocelot_get_stats64(struct net_device *dev,
 	struct ocelot *ocelot = priv->port.ocelot;
 	int port = priv->port.index;
 
+	spin_lock(&ocelot->stats_lock);
+
 	/* Configure the port to read the stats from */
 	ocelot_write(ocelot, SYS_STAT_CFG_STAT_VIEW(port),
 		     SYS_STAT_CFG);
@@ -758,6 +760,8 @@ static void ocelot_get_stats64(struct net_device *dev,
 	stats->tx_dropped = ocelot_read(ocelot, SYS_COUNT_TX_DROPS) +
 			    ocelot_read(ocelot, SYS_COUNT_TX_AGING);
 	stats->collisions = ocelot_read(ocelot, SYS_COUNT_TX_COLLISION);
+
+	spin_unlock(&ocelot->stats_lock);
 }
 
 static int ocelot_port_fdb_add(struct ndmsg *ndm, struct nlattr *tb[],