netdev - Re: [PATCH net-next] net: phy: fix regression with AX88772A PHY driver

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Message-ID: <eeb31d51-2b07-4b23-a844-c4112c34ef83@lunn.ch>
Date: Mon, 18 Sep 2023 15:49:32 +0200
From: Andrew Lunn <andrew@...n.ch>
To: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: phy: fix regression with AX88772A PHY
 driver

On Mon, Sep 18, 2023 at 02:25:36PM +0100, Russell King (Oracle) wrote:
> Marek reports that a deadlock occurs with the AX88772A PHY used on the
> ASIX USB network driver:
> 
> asix 1-1.4:1.0 (unnamed net_device) (uninitialized): PHY [usb-001:003:10] driver [Asix Electronics AX88772A] (irq=POLL)
> Asix Electronics AX88772A usb-001:003:10: attached PHY driver(mii_bus:phy_addr=usb-001:003:10, irq=POLL)
> asix 1-1.4:1.0 eth0: register 'asix' at usb-12110000.usb-1.4, ASIX AX88772 USB 2.0 Ethernet, a2:99:b6:cd:11:eb
> asix 1-1.4:1.0 eth0: configuring for phy/internal link mode
> 
> ============================================
> WARNING: possible recursive locking detected
> 6.6.0-rc1-00239-g8da77df649c4-dirty #13949 Not tainted
> --------------------------------------------
> kworker/3:3/71 is trying to acquire lock:
> c6c704cc (&dev->lock){+.+.}-{3:3}, at: phy_start_aneg+0x1c/0x38
> 
> but task is already holding lock:
> c6c704cc (&dev->lock){+.+.}-{3:3}, at: phy_state_machine+0x100/0x2b8
> 
> This is because we now consistently call phy_process_state_change()
> while holding phydev->lock, but the AX88772A PHY driver then goes on
> to call phy_start_aneg() which tries to grab the same lock - causing
> deadlock.
> 
> Fix this by exporting the unlocked version, and use this in the PHY
> driver instead.
> 
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Fixes: ef113a60d0a9 ("net: phy: call phy_error_precise() while holding the lock")
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>

Hi Russell

Yes, this fixes the problem for stable.

Reviewed-by: Andrew Lunn <andrew@...n.ch>

But maybe it would be better to move the hardware workaround into the
PHY driver? Its the PHY which is broken, so why is the MAC working
around it?

       Andrew