linux-kernel - Re: [PATCH net v1 1/1] net: usb: asix: forbid runtime PM to avoid PM/MDIO + RTNL deadlock

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Message-ID: <aMsEyXPMVWewOmQS@wunner.de>
Date: Wed, 17 Sep 2025 20:58:17 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Hubert Wi??niewski <hubert.wisniewski.25632@...il.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>, stable@...r.kernel.org,
	kernel@...gutronix.de, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Russell King <linux@...linux.org.uk>,
	Xu Yang <xu.yang_2@....com>, linux-usb@...r.kernel.org
Subject: Re: [PATCH net v1 1/1] net: usb: asix: forbid runtime PM to avoid
 PM/MDIO + RTNL deadlock

On Wed, Sep 17, 2025 at 11:54:57AM +0200, Oleksij Rempel wrote:
> Forbid USB runtime PM (autosuspend) for AX88772* in bind.
[...]
> With autosuspend active, resume paths may require calling phylink/phylib
> (caller must hold RTNL) and doing MDIO I/O. Taking RTNL from a USB PM
> resume can deadlock (RTNL may already be held), and MDIO can attempt a
> runtime-wake while the USB PM lock is held.

FWIW, for smsc95xx.c, the MDIO deadlock issue was resolved by commit
7b960c967f2a ("usbnet: smsc95xx: Fix deadlock on runtime resume").
I would assume that something similar would be possible for
asix_devices.c as well.

Thanks,

Lukas