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

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

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);
}

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.

Johan