linux-kernel - Re: [PATCH net-next] net: phy: Add driver for Motorcomm yt8531 gigabit ethernet phy

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Date:   Wed, 30 Nov 2022 17:33:15 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Frank <Frank.Sae@...or-comm.com>, Peter Geis <pgwipeout@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, yinghong.zhang@...or-comm.com,
        fei.zhang@...or-comm.com, hua.sun@...or-comm.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: phy: Add driver for Motorcomm yt8531
 gigabit ethernet phy

Hi Andrew,

On Wed, Nov 30, 2022 at 06:10:42PM +0100, Andrew Lunn wrote:
> This is not the first time Russell has pointed out your locking is
> wrong.
> 
> How about adding a check in functions which should be called with the
> lock taken really do have the lock taken?

They already do:

        lockdep_assert_held_once(&bus->mdio_lock);

but I guess people just aren't testing their code with lockdep enabled.

The only other thing I can think of trying is to use mutex_trylock():

	if (WARN_ON_ONCE(mutex_trylock(&bus->mdio_lock)))
		mutex_unlock(&bus->mdio_lock);

scattered throughout.

However, if the author does have lockdep enabled but ignores the
warnings, that isn't going to help.

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