[PATCH net v7 1/2] net: phylink: unwind the PHY binding when bringup fails late

[Aleksei Sviridkin <f@lex.la>]

phylink_bringup_phy() records the PHY in pl->phydev before its last
fallible step: on a MAC whose phylink ops implement LPI,
phy_eee_rx_clock_stop() can fail with a real MDIO error. The callers
unwind with phy_detach(), which knows nothing about pl->phydev, so a
pointer to a PHY that is no longer attached outlives the failed
connect.

What that costs depends on how the caller got here.
phylink_connect_phy() goes through phylink_attach_phy(), which refuses
to attach while pl->phydev is set, turning a transient MDIO error into
a permanent -EBUSY. The SFP path is worse than that: sfp_sm_probe_phy()
answers the failure with phy_device_remove() and phy_device_free(), and
it assigns sfp->mod_phy only past that error return, so nothing clears
pl->phydev and it is left pointing at a freed phy_device that
phylink_resolve() and the ethtool helpers go on reading.
phylink_fwnode_phy_connect() has no such check, so a later connect
overwrites the stale pointer and hides the problem. A disconnect does
not: phylink_disconnect_phy() hands that pointer to phy_disconnect(),
and the second phy_detach() on the same PHY drops references the first
one already released.

Clear the binding on the failure path. This is the same operation
phylink_disconnect_phy() performs, so both now share a helper. The
PHY-side fields are left to phy_detach(), which every caller already
runs on this path.

Fixes: 03abf2a7c654 ("net: phylink: add EEE management")
Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <f@lex.la>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
 drivers/net/phy/phylink.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 3ec3bb439109..6a92fac58f25 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -2083,6 +2083,18 @@ static int phylink_validate_phy(struct phylink *pl, struct phy_device *phy,
 	return phylink_validate(pl, supported, state);
 }
 
+/* Disassociate @phy from @pl. Caller must hold pl->phydev_mutex. */
+static void phylink_clear_phydev(struct phylink *pl, struct phy_device *phy)
+{
+	mutex_lock(&phy->lock);
+	mutex_lock(&pl->state_mutex);
+	pl->phydev = NULL;
+	pl->phy_enable_tx_lpi = false;
+	pl->mac_tx_clk_stop = false;
+	mutex_unlock(&pl->state_mutex);
+	mutex_unlock(&phy->lock);
+}
+
 static int phylink_bringup_phy(struct phylink *pl, struct phy_device *phy,
 			       phy_interface_t interface)
 {
@@ -2197,6 +2209,12 @@ static int phylink_bringup_phy(struct phylink *pl, struct phy_device *phy,
 	if (ret == 0 && phy_interrupt_is_valid(phy))
 		phy_request_interrupt(phy);
 
+	if (ret) {
+		mutex_lock(&pl->phydev_mutex);
+		phylink_clear_phydev(pl, phy);
+		mutex_unlock(&pl->phydev_mutex);
+	}
+
 	return ret;
 }
 
@@ -2347,15 +2365,8 @@ void phylink_disconnect_phy(struct phylink *pl)
 
 	mutex_lock(&pl->phydev_mutex);
 	phy = pl->phydev;
-	if (phy) {
-		mutex_lock(&phy->lock);
-		mutex_lock(&pl->state_mutex);
-		pl->phydev = NULL;
-		pl->phy_enable_tx_lpi = false;
-		pl->mac_tx_clk_stop = false;
-		mutex_unlock(&pl->state_mutex);
-		mutex_unlock(&phy->lock);
-	}
+	if (phy)
+		phylink_clear_phydev(pl, phy);
 	mutex_unlock(&pl->phydev_mutex);
 
 	if (phy) {
-- 
2.53.0