Patch "phy state machine: failsafe leave invalid RUNNING state" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

phy state machine: failsafe leave invalid RUNNING state

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
phy-state-machine-failsafe-leave-invalid-running-state.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Zefir Kurtisi <[email protected]>
Date: Fri, 6 Jan 2017 12:14:48 +0100
Subject: phy state machine: failsafe leave invalid RUNNING state

From: Zefir Kurtisi <[email protected]>

[ Upstream commit 811a919135b980bac8009d042acdccf10dc1ef5e ]

While in RUNNING state, phy_state_machine() checks for link changes by comparing phydev->link before and after calling phy_read_status(). This works as long as it is guaranteed that phydev->link is never changed outside the phy_state_machine().

If in some setups this happens, it causes the state machine to miss a link loss and remain RUNNING despite phydev->link being 0.

This has been observed running a dsa setup with a process continuously polling the link states over ethtool each second (SNMPD RFC-1213 agent). Disconnecting the link on a phy followed by a ETHTOOL_GSET causes dsa_slave_get_settings() / dsa_slave_get_link_ksettings() to call phy_read_status() and with that modify the link status - and with that bricking the phy state machine.

This patch adds a fail-safe check while in RUNNING, which causes to move to CHANGELINK when the link is gone and we are still RUNNING.

---
 drivers/net/phy/phy.c |    9 +++++++++
 1 file changed, 9 insertions(+)

@@ -1063,6 +1063,15 @@ void phy_state_machine(struct work_struc
 			if (old_link != phydev->link)
 				phydev->state = PHY_CHANGELINK;
 		}
+		/*
+		 * Failsafe: check that nobody set phydev->link=0 between two
+		 * poll cycles, otherwise we won't leave RUNNING state as long
+		 * as link remains down.
+		 */
+		if (!phydev->link && phydev->state == PHY_RUNNING) {
+			phydev->state = PHY_CHANGELINK;
+			phydev_err(phydev, "no link in PHY_RUNNING\n");
+		}
 		break;
 	case PHY_CHANGELINK:
 		err = phy_read_status(phydev);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/phy-state-machine-failsafe-leave-invalid-running-state.patch