linux-kernel - Re: [PATCH] net: mdio: octeon: Fix some double free issues

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Date:   Thu, 13 May 2021 10:44:15 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     andrew@...n.ch, hkallweit1@...il.com, davem@...emloft.net,
        kuba@...nel.org, f.fainelli@...il.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] net: mdio: octeon: Fix some double free issues

On Thu, May 13, 2021 at 09:24:55AM +0200, Christophe JAILLET wrote:
> 'bus->mii_bus' has been allocated with 'devm_mdiobus_alloc_size()' in the
> probe function. So it must not be freed explicitly or there will be a
> double free.
> 
> Remove the incorrect 'mdiobus_free' in the error handling path of the
> probe function and in remove function.
> 
> Suggested-By: Andrew Lunn <andrew@...n.ch>
> Fixes: 35d2aeac9810 ("phy: mdio-octeon: Use devm_mdiobus_alloc_size()")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>

Reviewed-by: Russell King <rmk+kernel@...linux.org.uk>

> ---
> The 'smi_en.u64 = 0; oct_mdio_writeq()' looks odd to me. Usually the normal
> path and the error handling path don't write the same value. Here, both
> write 0.
> Having '1' somewhere would 'look' more usual. :)
> More over I think that 'smi_en.s.en = 1;' in the probe is useless.

It looks fine to me.

        smi_en.u64 = 0;
        smi_en.s.en = 1;
        oct_mdio_writeq(smi_en.u64, bus->register_base + SMI_EN);

smi_en is a union of a u64 and a structure containing a bitfield. s.en
corresponds on LE systems with the u64 bit 0. So the above has the
effect of writing a u64 value of '1' to the SMI_EN register, whereas:

        smi_en.u64 = 0;
        oct_mdio_writeq(smi_en.u64, bus->register_base + SMI_EN);

has the effect of writing a u64 value of '0' to the SMI_EN register.

This code is fine.

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