netdev - Re: [PATCH net-next] net: phy: avoid kernel warning dump when stopping an errored PHY

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Date: Mon, 22 May 2023 17:06:47 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: phy: avoid kernel warning dump when
 stopping an errored PHY

On Mon, May 22, 2023 at 04:58:08PM +0100, Russell King (Oracle) wrote:
> When taking a network interface down (or removing a SFP module) after
> the PHY has encountered an error, phy_stop() complains incorrectly
> that it was called from HALTED state.
> 
> The reason this is incorrect is that the network driver will have
> called phy_start() when the interface was brought up, and the fact
> that the PHY has a problem bears no relationship to the administrative
> state of the interface. Taking the interface administratively down
> (which calls phy_stop()) is always the right thing to do after a
> successful phy_start() call, whether or not the PHY has encountered
> an error.

Note that I can reproduce this by repeatedly plugging and unplugging any
SFP with a PHY that we access - if one unplugs it while the PHY is being
accessed, phylib logs an error, and then the unplug event happens which
ends up correctly calling phy_stop(), which then spits out a kernel
warning.

One may suggest that this is an unlikely event, but any SFP using the
Rollball I2C protocol to access the PHY, each access can take tens of
milliseconds, which is more than enough time to hit this.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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