linux-kernel - Re: [PATCH net-next v2 01/10] net: dsa: lan9303: Fixed MDIO interface

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Message-ID: <20170728133637.GB32230@lunn.ch>
Date:   Fri, 28 Jul 2017 15:36:37 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Egil Hjelmeland <privat@...l-hjelmeland.no>
Cc:     corbet@....net, vivien.didelot@...oirfairelinux.com,
        f.fainelli@...il.com, davem@...emloft.net, kernel@...gutronix.de,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 01/10] net: dsa: lan9303: Fixed MDIO interface

On Fri, Jul 28, 2017 at 01:08:25PM +0200, Egil Hjelmeland wrote:
> On 26. juli 2017 18:55, Andrew Lunn wrote:
> >On Tue, Jul 25, 2017 at 06:15:44PM +0200, Egil Hjelmeland wrote:
> >It is better to use mdiobus_read/write or if you are nesting mdio
> >busses, mdiobus_read_nested/mdiobus_write_nested. Please test this
> >code with lockdep enabled.
> >
> 
> I have CONFIG_DEBUG_SPINLOCK, CONFIG_DEBUG_MUTEXES. Should I enable
> more?

Hi Egil

Enable CONFIG_LOCKDEP and CONFIG_PROVE_LOCKING.

Any lockdep splat you get while accessing the mdio bus at this point
are probably false positives, since it is a different mutex. Using the
_nested() version should avoid these false positives. But you might
find other places your locking is not right.

	Andrew