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: <0f2fe17b-89bb-4464-890d-0b73ed1cf117@suse.com>
Date: Wed, 17 Sep 2025 12:10:48 +0200
From: Oliver Neukum <oneukum@...e.com>
To: Oleksij Rempel <o.rempel@...gutronix.de>,
 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>
Cc: Hubert Wiśniewski <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,
 Lukas Wunner <lukas@...ner.de>, 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

Hi,

On 17.09.25 11:54, Oleksij Rempel wrote:

> 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. Given the lack of benefit
> and poor test coverage (autosuspend is usually disabled by default in
> distros), forbid runtime PM here to avoid these hazards.

This reasoning depends on netif_running() returning false during system resume.
Is that guaranteed?

	Regards
		Oliver