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

On Thu, Nov 17, 2016 at 10:52:25AM +0100, Johan Hovold wrote:

On Wed, Nov 16, 2016 at 10:14:10AM -0800, Florian Fainelli wrote:

quoted

On 11/16/2016 09:11 AM, Johan Hovold wrote:

quoted

On Wed, Nov 16, 2016 at 09:06:26AM -0800, Florian Fainelli wrote:

quoted

On 11/16/2016 06:47 AM, Johan Hovold wrote:

quoted

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@kernel.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.

quoted

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);

On second thought, I suggest just renaming the phy_device_free() as
phy_device_put() to reflect what it really does these days. There can
never be a guarantee that the phy is freed on a call to
phy_device_free() anyway.

The OF interface can still be modified to return a pointer later.

Johan