linux-kernel - Re: [PATCH] net: dsa: fix fixed-link-phy device leaks

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Date:   Thu, 17 Nov 2016 10:52:25 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Johan Hovold <johan@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: fix fixed-link-phy device leaks

On Wed, Nov 16, 2016 at 10:14:10AM -0800, Florian Fainelli wrote:
> On 11/16/2016 09:11 AM, Johan Hovold wrote:
> > On Wed, Nov 16, 2016 at 09:06:26AM -0800, Florian Fainelli wrote:
> >> On 11/16/2016 06:47 AM, Johan Hovold wrote:
> >>> Make sure to drop the reference taken by of_phy_find_device() when
> >>> registering and deregistering the fixed-link PHY-device.
> >>>
> >>> Note that we need to put both references held at deregistration.
> >>>
> >>> Fixes: 39b0c705195e ("net: dsa: Allow configuration of CPU & DSA port
> >>> speeds/duplex")
> >>> Signed-off-by: Johan Hovold <johan@...nel.org>
> >>> ---
> >>>
> >>> Hi,
> >>>
> >>> This is one has been compile tested only, but fixes a couple of leaks
> >>> similar to one that was found in the cpsw driver for which I just posted
> >>> a patch.
> >>>
> >>> It turns out all drivers but DSA fail to deregister the fixed-link PHYs
> >>> registered by of_phy_register_fixed_link(). Due to the way this
> >>> interface was designed, deregistering such a PHY is a bit cumbersome and
> >>> looks like it would benefit from a common helper.
> >>>
> >>> However, perhaps the interface should instead be changed so that the PHY
> >>> device is returned so that drivers do not need to use
> >>> of_phy_find_device() when they need to access properties of the fixed
> >>> link (e.g. as in dsu_cpu_dsa_setup below).
> >>>
> >>> Thoughts?
> >>>
> >>> Thanks,
> >>> Johan
> >>>
> >>>
> >>>  net/dsa/dsa.c | 8 +++++++-
> >>>  1 file changed, 7 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/net/dsa/dsa.c b/net/dsa/dsa.c
> >>> index a6902c1e2f28..798a6a776a5f 100644
> >>> --- a/net/dsa/dsa.c
> >>> +++ b/net/dsa/dsa.c
> >>> @@ -233,6 +233,8 @@ int dsa_cpu_dsa_setup(struct dsa_switch *ds, struct device *dev,
> >>>  		genphy_read_status(phydev);
> >>>  		if (ds->ops->adjust_link)
> >>>  			ds->ops->adjust_link(ds, port, phydev);
> >>> +
> >>> +		phy_device_free(phydev);	/* of_phy_find_device */
> >>>  	}
> >>>  
> >>>  	return 0;
> >>> @@ -509,8 +511,12 @@ void dsa_cpu_dsa_destroy(struct device_node *port_dn)
> >>>  	if (of_phy_is_fixed_link(port_dn)) {
> >>>  		phydev = of_phy_find_device(port_dn);
> >>>  		if (phydev) {
> >>> -			phy_device_free(phydev);
> >>>  			fixed_phy_unregister(phydev);
> >>> +			/* Put references taken by of_phy_find_device() and
> >>> +			 * of_phy_register_fixed_link().
> >>> +			 */
> >>> +			phy_device_free(phydev);
> >>> +			phy_device_free(phydev);
> >>
> >> Double free, this looks bogus here. Actually would not this mean a
> >> triple free since you already free in dsa_cpu_dsa_setup() which is
> >> paired with dsa_cpu_dsa_destroy()?
> > 
> > The naming of phy_device_free() is unfortunate when it's really a put():
> > 
> > void phy_device_free(struct phy_device *phydev)
> > {
> > 	put_device(&phydev->mdio.dev);
> > }
> 
> Indeed, should have looked a little harder.
> 
> > 
> > which may need to be called multiple times, specifically after a call to
> > of_phy_find_device() which takes another reference.
> > 
> > With this patch the refcounts are properly balanced.
> 
> The intent of your patch is good, but it still feels like having to
> double imbalance the refcount is symptomatic of a larger issue here, it
> does not seem like having several refcounts are necessary, so we may
> really want to rework the API.

I'll cook something up for -next, but how about using

	put_device(&phydev->mdio.dev)

for the reference taken by of_phy_find_device() (as some driver
already do) to fix the immediate leaks?

Then deregistration would look like:

	phydev = of_phy_find_device(port_dn);
	if (phydev) {
-			phy_device_free(phydev);
			fixed_phy_unregister(phydev);
+			put_device(&phydev->mdio.dev)
+			phy_device_free(phydev);

Thanks,
Johan