[PATCH net-next 1/3] 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() and the SFP path go through
phylink_attach_phy(), which refuses to attach while pl->phydev is set
and turns a transient MDIO error into a permanent -EBUSY.
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 a device reference
and two module references that were only ever taken once.

Clear the binding on the failure path, the same three fields
phylink_disconnect_phy() clears, under the same locks. The PHY-side
fields are left to phy_detach(), which every caller already runs on
this path.

Signed-off-by: Aleksei Sviridkin <f@lex.la>
---
Reachability

The failing step needs pl->mac_supports_eee_ops, i.e. a MAC whose
phylink ops implement the LPI callbacks; mt7530 is one, and on the
board I tested ethtool --show-eee returns -EOPNOTSUPP, which is what
phylink reports when mac_supports_eee_ops is set and mac_supports_eee
is not, so that tail runs on every bringup there. The error itself is
an MDIO transaction failure inside phy_eee_rx_clock_stop(), which
cannot be produced deliberately, so this patch is compile-tested and
the series it belongs to ran on hardware with it in place.

The double-detach path needs a port that outlives a failed connect,
which is what patch 3 introduces; before that, DSA destroyed the port
immediately and the stale pointer went with it.
 drivers/net/phy/phylink.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
index 5b8e95690..9d403ff1b 100644
--- a/drivers/net/phy/phylink.c
+++ b/drivers/net/phy/phylink.c
@@ -2197,6 +2197,18 @@ 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);
+		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);
+		mutex_unlock(&pl->phydev_mutex);
+	}
+
 	return ret;
 }
 
-- 
2.43.0