From 06efc9b8a1360cad83cae6e71558e5458cc1fbf3 Mon Sep 17 00:00:00 2001 From: Vladimir Oltean Date: Tue, 29 Nov 2022 16:12:14 +0200 Subject: [PATCH 07/14] net: dpaa2-eth: assign priv->mac after dpaa2_mac_connect() call There are 2 requirements for correct code: - Any time the driver accesses the priv->mac pointer at runtime, it either holds NULL to indicate a DPNI-DPNI connection (or unconnected DPNI), or a struct dpaa2_mac whose phylink instance was fully initialized (created and connected to the PHY). No changes are made to priv->mac while it is being used. Currently, rtnl_lock() watches over the call to dpaa2_eth_connect_mac(), so it serves the purpose of serializing this with all readers of priv->mac. - dpaa2_mac_connect() should run unlocked, because inside it are 2 phylink calls with incompatible locking requirements: phylink_create() requires that the rtnl_mutex isn't held, and phylink_fwnode_phy_connect() requires that the rtnl_mutex is held. The only way to solve those contradictory requirements is to let dpaa2_mac_connect() take rtnl_lock() when it needs to. To solve both requirements, we need to identify the writer side of the priv->mac pointer, which can be wrapped in a mutex private to the driver in a future patch. The dpaa2_mac_connect() cannot be part of the writer side critical section, because of an AB/BA deadlock with rtnl_lock(). So the strategy needs to be that where we prepare the DPMAC by calling dpaa2_mac_connect(), and only make priv->mac point to it once it's fully prepared. This ensures that the writer side critical section has the absolute minimum surface it can. The reverse strategy is adopted in the dpaa2_eth_disconnect_mac() code path. This makes sure that priv->mac is NULL when we start tearing down the DPMAC that we disconnected from, and concurrent code will simply not see it. No locking changes in this patch (concurrent code is still blocked by the rtnl_mutex). Signed-off-by: Vladimir Oltean Reviewed-by: Ioana Ciornei Tested-by: Ioana Ciornei Signed-off-by: Paolo Abeni --- .../net/ethernet/freescale/dpaa2/dpaa2-eth.c | 21 +++++++++++-------- 1 file changed, 12 insertions(+), 9 deletions(-) --- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c +++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c @@ -4441,9 +4441,8 @@ static int dpaa2_eth_connect_mac(struct err = dpaa2_mac_open(mac); if (err) goto err_free_mac; - priv->mac = mac; - if (dpaa2_eth_is_type_phy(priv)) { + if (dpaa2_mac_is_type_phy(mac)) { err = dpaa2_mac_connect(mac); if (err && err != -EPROBE_DEFER) netdev_err(priv->net_dev, "Error connecting to the MAC endpoint: %pe", @@ -4452,11 +4451,12 @@ static int dpaa2_eth_connect_mac(struct goto err_close_mac; } + priv->mac = mac; + return 0; err_close_mac: dpaa2_mac_close(mac); - priv->mac = NULL; err_free_mac: kfree(mac); return err; @@ -4464,15 +4464,18 @@ err_free_mac: static void dpaa2_eth_disconnect_mac(struct dpaa2_eth_priv *priv) { - if (dpaa2_eth_is_type_phy(priv)) - dpaa2_mac_disconnect(priv->mac); + struct dpaa2_mac *mac = priv->mac; + + priv->mac = NULL; - if (!dpaa2_eth_has_mac(priv)) + if (!mac) return; - dpaa2_mac_close(priv->mac); - kfree(priv->mac); - priv->mac = NULL; + if (dpaa2_mac_is_type_phy(mac)) + dpaa2_mac_disconnect(mac); + + dpaa2_mac_close(mac); + kfree(mac); } static irqreturn_t dpni_irq0_handler_thread(int irq_num, void *arg)