Re: [PATCH net-next] net: mdio: get/put device node during (un)registration

Russell King (Oracle)
2024-01-03T12:01:17Z

On Wed, Jan 03, 2024 at 10:22:00AM +0000, Russell King (Oracle) wrote:
> I agree with that approach, but as you rightly point out, we need MDIO
> to behave correctly, and I don't think that patching just one bit of
> MDIO to fix this mess is the right approach.

This is probably a safer approach to ensuring that the firmware data
reference count isn't dropped while the bus exists byensuring that we
always take a reference at register time. It also likely fixes similar
issues with ACPI and swnode based users as well.

It doesn't deal with the excess-refcount problem, as with this approach
the two issues are entirely independent of each other.

Please test to check that this addresses your issue. Thanks.

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 6cf73c15635b..afbad1ad8683 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -193,6 +193,10 @@ static void mdiobus_release(struct device *d)
bus->state != MDIOBUS_ALLOCATED,
"%s: not in RELEASED or ALLOCATED state\n",
bus->id);
+
+ if (bus->state == MDIOBUS_RELEASED)
+ fwnode_handle_put(dev_fwnode(d));
+
kfree(bus);
}

@@ -684,6 +688,15 @@ int __mdiobus_register(struct mii_bus *bus, struct module *owner)
bus->dev.groups = NULL;
dev_set_name(&bus->dev, "%s", bus->id);

+ /* If the bus state is allocated, we're registering a fresh bus
+ * that may have a fwnode associated with it. Grab a reference
+ * to the fwnode. This will be dropped when the bus is released.
+ * If the bus was set to unregistered, it means that the bus was
+ * previously registered, and we've already grabbed a reference.
+ */
+ if (bus->state == MDIOBUS_ALLOCATED)
+ fwnode_handle_get(dev_fwnode(&bus->dev));
+
/* We need to set state to MDIOBUS_UNREGISTERED to correctly release
* the device in mdiobus_free()
*
--
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