netdev - Re: [PATCH net-next v1 1/1] net: dsa: ar9331: fix potential dead lock on mdio access

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Date:   Thu, 16 Jun 2022 17:30:57 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v1 1/1] net: dsa: ar9331: fix potential dead
 lock on mdio access

On Thu, Jun 16, 2022 at 03:34:18PM +0200, Andrew Lunn wrote:
> >  static int ar9331_mdio_read(void *ctx, const void *reg_buf, size_t reg_len,
> > @@ -849,6 +849,8 @@ static int ar9331_mdio_read(void *ctx, const void *reg_buf, size_t reg_len,
> >  		return 0;
> >  	}
> >  
> > +	mutex_lock_nested(&sbus->mdio_lock, MDIO_MUTEX_NESTED);
> > +
> 
> Do you know about mdiobus_read_nested() and
> mdiobus_write_nested(). The mv88e6xxx driver uses these.

Yes.

I need at least 2 master MDIO accesses to implement 1 slave mdio access.
So I decided to get lock one time for all needed accesses instead of
taking it multiple times.

Regards,
Oleksij
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