Subject: Re: [PATCH net-next 1/7] net: phy: always call phy_process_state_change() under lock

From: "Russell King (Oracle)" <[email-masked]>
Date: Mon, 18 Sep 2023 14:06:26 +0100

On Mon, Sep 18, 2023 at 02:33:04PM +0200, Marek Szyprowski wrote:
> Hi Russell,
> 
> On 14.09.2023 17:35, Russell King (Oracle) wrote:
> > phy_stop() calls phy_process_state_change() while holding the phydev
> > lock, so also arrange for phy_state_machine() to do the same, so that
> > this function is called with consistent locking.
> >
> > Tested-by: Jijie Shao <[email-masked]>
> > Signed-off-by: Russell King (Oracle) <[email-masked]>
> 
> This change, merged to linux-next as commit 8da77df649c4 ("net: phy: 
> always call phy_process_state_change() under lock") introduces the 
> following deadlock with ASIX AX8817X USB driver:

Yay, latent bug found...

I guess this is asix_ax88772a_link_change_notify() which is causing
the problem, and yes, that phy_start_aneg() needs to be the unlocked
version (which we'll have to export.)

This should fix it.

diff --git a/drivers/net/phy/ax88796b.c b/drivers/net/phy/ax88796b.c
index 0f1e617a26c9..eb74a8cf8df1 100644
--- a/drivers/net/phy/ax88796b.c
+++ b/drivers/net/phy/ax88796b.c
@@ -90,7 +90,7 @@ static void asix_ax88772a_link_change_notify(struct phy_device *phydev)
 	 */
 	if (phydev->state == PHY_NOLINK) {
 		phy_init_hw(phydev);
-		phy_start_aneg(phydev);
+		_phy_start_aneg(phydev);
 	}
 }
 
diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index 93a8676dd8d8..a5fa077650e8 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -981,7 +981,7 @@ static int phy_check_link_status(struct phy_device *phydev)
  *   If the PHYCONTROL Layer is operating, we change the state to
  *   reflect the beginning of Auto-negotiation or forcing.
  */
-static int _phy_start_aneg(struct phy_device *phydev)
+int _phy_start_aneg(struct phy_device *phydev)
 {
 	int err;
 
@@ -1002,6 +1002,7 @@ static int _phy_start_aneg(struct phy_device *phydev)
 
 	return err;
 }
+EXPORT_SYMBOL(_phy_start_aneg);
 
 /**
  * phy_start_aneg - start auto-negotiation for this PHY device
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 1351b802ffcf..3cc52826f18e 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -1736,6 +1736,7 @@ void phy_detach(struct phy_device *phydev);
 void phy_start(struct phy_device *phydev);
 void phy_stop(struct phy_device *phydev);
 int phy_config_aneg(struct phy_device *phydev);
+int _phy_start_aneg(struct phy_device *phydev);
 int phy_start_aneg(struct phy_device *phydev);
 int phy_aneg_done(struct phy_device *phydev);
 int phy_speed_down(struct phy_device *phydev, bool sync);
-- 
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