linux-kernel - [PATCH net-next 12/12] net: dpaa2-mac: move rtnl_lock() only around phylink_{,dis}connect

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Date:   Tue, 29 Nov 2022 16:12:21 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     Ioana Ciornei <ioana.ciornei@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net-next 12/12] net: dpaa2-mac: move rtnl_lock() only around phylink_{,dis}connect_phy()

After the introduction of a private mac_lock that serializes access to
priv->mac (and port_priv->mac in the switch), the only remaining purpose
of rtnl_lock() is to satisfy the locking requirements of
phylink_fwnode_phy_connect() and phylink_disconnect_phy().

But the functions these live in, dpaa2_mac_connect() and
dpaa2_mac_disconnect(), have contradictory locking requirements.
While phylink_fwnode_phy_connect() wants rtnl_lock() to be held,
phylink_create() wants it to not be held.

Move the rtnl_lock() from top-level (in the dpaa2-eth and dpaa2-switch
drivers) to only surround the phylink calls that require it, in the
dpaa2-mac library code.

This is possible because dpaa2_mac_connect() and dpaa2_mac_disconnect()
run unlocked, and there isn't any danger of an AB/BA deadlock between
the rtnl_mutex and other private locks.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c    | 4 ----
 drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c    | 5 +++++
 drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c | 4 ----
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
index 3ed54c147e98..0c35abb7d065 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c
@@ -4715,7 +4715,6 @@ static irqreturn_t dpni_irq0_handler_thread(int irq_num, void *arg)
 		dpaa2_eth_set_mac_addr(netdev_priv(net_dev));
 		dpaa2_eth_update_tx_fqids(priv);
 
-		rtnl_lock();
 		/* We can avoid locking because the "endpoint changed" IRQ
 		 * handler is the only one who changes priv->mac at runtime,
 		 * so we are not racing with anyone.
@@ -4725,7 +4724,6 @@ static irqreturn_t dpni_irq0_handler_thread(int irq_num, void *arg)
 			dpaa2_eth_disconnect_mac(priv);
 		else
 			dpaa2_eth_connect_mac(priv);
-		rtnl_unlock();
 	}
 
 	return IRQ_HANDLED;
@@ -5045,9 +5043,7 @@ static int dpaa2_eth_remove(struct fsl_mc_device *ls_dev)
 	else
 		fsl_mc_free_irqs(ls_dev);
 
-	rtnl_lock();
 	dpaa2_eth_disconnect_mac(priv);
-	rtnl_unlock();
 	dpaa2_eth_free_rings(priv);
 	free_percpu(priv->fd);
 	free_percpu(priv->sgt_cache);
diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
index 9d1e7026eaef..8ba4ea4adeb3 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c
@@ -431,7 +431,9 @@ int dpaa2_mac_connect(struct dpaa2_mac *mac)
 	}
 	mac->phylink = phylink;
 
+	rtnl_lock();
 	err = phylink_fwnode_phy_connect(mac->phylink, dpmac_node, 0);
+	rtnl_unlock();
 	if (err) {
 		netdev_err(net_dev, "phylink_fwnode_phy_connect() = %d\n", err);
 		goto err_phylink_destroy;
@@ -449,7 +451,10 @@ int dpaa2_mac_connect(struct dpaa2_mac *mac)
 
 void dpaa2_mac_disconnect(struct dpaa2_mac *mac)
 {
+	rtnl_lock();
 	phylink_disconnect_phy(mac->phylink);
+	rtnl_unlock();
+
 	phylink_destroy(mac->phylink);
 	dpaa2_pcs_destroy(mac);
 	of_phy_put(mac->serdes_phy);
diff --git a/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c b/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c
index 0472e24191ad..f4ae4289c41a 100644
--- a/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c
+++ b/drivers/net/ethernet/freescale/dpaa2/dpaa2-switch.c
@@ -1529,7 +1529,6 @@ static irqreturn_t dpaa2_switch_irq0_handler_thread(int irq_num, void *arg)
 	}
 
 	if (status & DPSW_IRQ_EVENT_ENDPOINT_CHANGED) {
-		rtnl_lock();
 		/* We can avoid locking because the "endpoint changed" IRQ
 		 * handler is the only one who changes priv->mac at runtime,
 		 * so we are not racing with anyone.
@@ -1539,7 +1538,6 @@ static irqreturn_t dpaa2_switch_irq0_handler_thread(int irq_num, void *arg)
 			dpaa2_switch_port_disconnect_mac(port_priv);
 		else
 			dpaa2_switch_port_connect_mac(port_priv);
-		rtnl_unlock();
 	}
 
 out:
@@ -2957,9 +2955,7 @@ static void dpaa2_switch_remove_port(struct ethsw_core *ethsw,
 {
 	struct ethsw_port_priv *port_priv = ethsw->ports[port_idx];
 
-	rtnl_lock();
 	dpaa2_switch_port_disconnect_mac(port_priv);
-	rtnl_unlock();
 	free_netdev(port_priv->netdev);
 	ethsw->ports[port_idx] = NULL;
 }
-- 
2.34.1