linux-kernel - Re: [PATCH 5.10 64/98] net: mdio-mux: Handle -EPROBE

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Date:   Tue, 24 Aug 2021 12:34:33 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Marc Zyngier <maz@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH 5.10 64/98] net: mdio-mux: Handle -EPROBE_DEFER correctly

On Tue, Aug 24, 2021 at 12:00 PM Pavel Machek <pavel@...x.de> wrote:
>
> Hi1
>
> > When registering mdiobus children, if we get an -EPROBE_DEFER, we shouldn't
> > ignore it and continue registering the rest of the mdiobus children. This
> > would permanently prevent the deferring child mdiobus from working instead
> > of reattempting it in the future. So, if a child mdiobus needs to be
> > reattempted in the future, defer the entire mdio-mux initialization.
> >
> > This fixes the issue where PHYs sitting under the mdio-mux aren't
> > initialized correctly if the PHY's interrupt controller is not yet ready
> > when the mdio-mux is being probed. Additional context in the link
> > below.
>
> I don't believe this is quite right. AFAICT it leaks memory in the
> EPROBE_DEFER case. Could someone double-check? Suggested fix is below.

devm_ APIs would take care of releasing the resource (memory)
automatically because the probe didn't succeed. So I'm not sure
there's a leak. Does that make sense?

-Saravana

>
> > +++ b/drivers/net/mdio/mdio-mux.c
> > @@ -175,11 +175,15 @@ int mdio_mux_init(struct device *dev,
> >               cb->mii_bus->write = mdio_mux_write;
> >               r = of_mdiobus_register(cb->mii_bus, child_bus_node);
> >               if (r) {
> > +                     mdiobus_free(cb->mii_bus);
> > +                     if (r == -EPROBE_DEFER) {
> > +                             ret_val = r;
> > +                             goto err_loop;
> > +                     }
> > +                     devm_kfree(dev, cb);
> >                       dev_err(dev,
> >                               "Error: Failed to register MDIO bus for child %pOF\n",
> >                               child_bus_node);
> > -                     mdiobus_free(cb->mii_bus);
> > -                     devm_kfree(dev, cb);
> >               } else {
> >                       cb->next = pb->children;
> >                       pb->children = cb;
>
>
> Signed-off-by: Pavel Machek (CIP) <pavel@...x.de>
>
> diff --git a/drivers/net/mdio/mdio-mux.c b/drivers/net/mdio/mdio-mux.c
> index ccb3ee704eb1..6d0e505343c5 100644
> --- a/drivers/net/mdio/mdio-mux.c
> +++ b/drivers/net/mdio/mdio-mux.c
> @@ -163,6 +163,7 @@ int mdio_mux_init(struct device *dev,
>                 cb->mii_bus = mdiobus_alloc();
>                 if (!cb->mii_bus) {
>                         ret_val = -ENOMEM;
> +                       devm_kfree(dev, cb);
>                         goto err_loop;
>                 }
>                 cb->mii_bus->priv = cb;
> @@ -176,11 +177,11 @@ int mdio_mux_init(struct device *dev,
>                 r = of_mdiobus_register(cb->mii_bus, child_bus_node);
>                 if (r) {
>                         mdiobus_free(cb->mii_bus);
> +                       devm_kfree(dev, cb);
>                         if (r == -EPROBE_DEFER) {
>                                 ret_val = r;
>                                 goto err_loop;
>                         }
> -                       devm_kfree(dev, cb);
>                         dev_err(dev,
>                                 "Error: Failed to register MDIO bus for child %pOF\n",
>                                 child_bus_node);
>
>
> --
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany