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[PATCH 3/9] phy: fix mdiobus module safety

From Russell King <rmk+kernel@arm.linux.org.uk>
Newsgroups linux.kernel
Subject [PATCH 3/9] phy: fix mdiobus module safety
Date 2015-09-22 18:20 +0200
Message-ID <qbysq-219-33@gated-at.bofh.it> (permalink)
References <qbysp-219-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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Re-implement the mdiobus module refcounting to ensure that we actually
ensure that the mdiobus module code does not go away while we might call
into it.

The old scheme using bus->dev.driver was buggy, because bus->dev is a
class device which never has a struct device_driver associated with it,
and hence the associated code trying to obtain a refcount did nothing
useful.

Instead, take the approach that other subsystems do: pass the module
when calling mdiobus_register(), and record that in the mii_bus struct.
When we need to increment the module use count in the phy code, use
this stored pointer.  When the phy is deteched, drop the module
refcount, remembering that the phy device might go away at that point.

This doesn't stop the mii_bus going away while there are in-use phys -
it merely stops the underlying code vanishing.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
 drivers/net/phy/mdio_bus.c   |  5 +++--
 drivers/net/phy/phy_device.c | 32 ++++++++++++++++++--------------
 include/linux/phy.h          |  5 ++++-
 3 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index 67553e13bd36..992406624b7c 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -244,7 +244,7 @@ static inline void of_mdiobus_link_phydev(struct mii_bus *mdio,
  *
  * Returns 0 on success or < 0 on error.
  */
-int mdiobus_register(struct mii_bus *bus)
+int __mdiobus_register(struct mii_bus *bus, struct module *owner)
 {
 	int i, err;
 
@@ -255,6 +255,7 @@ int mdiobus_register(struct mii_bus *bus)
 	BUG_ON(bus->state != MDIOBUS_ALLOCATED &&
 	       bus->state != MDIOBUS_UNREGISTERED);
 
+	bus->owner = owner;
 	bus->dev.parent = bus->parent;
 	bus->dev.class = &mdio_bus_class;
 	bus->dev.groups = NULL;
@@ -296,7 +297,7 @@ int mdiobus_register(struct mii_bus *bus)
 	device_del(&bus->dev);
 	return err;
 }
-EXPORT_SYMBOL(mdiobus_register);
+EXPORT_SYMBOL(__mdiobus_register);
 
 void mdiobus_unregister(struct mii_bus *bus)
 {
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index c0f211127274..03adf328f49b 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -582,10 +582,15 @@ EXPORT_SYMBOL(phy_init_hw);
 int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 		      u32 flags, phy_interface_t interface)
 {
+	struct mii_bus *bus = phydev->bus;
 	struct device *d = &phydev->dev;
-	struct module *bus_module;
 	int err;
 
+	if (!try_module_get(bus->owner)) {
+		dev_err(&dev->dev, "failed to get the bus module\n");
+		return -EIO;
+	}
+
 	/* Assume that if there is no driver, that it doesn't
 	 * exist, and we should use the genphy driver.
 	 */
@@ -600,20 +605,13 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 			err = device_bind_driver(d);
 
 		if (err)
-			return err;
+			goto error;
 	}
 
 	if (phydev->attached_dev) {
 		dev_err(&dev->dev, "PHY already attached\n");
-		return -EBUSY;
-	}
-
-	/* Increment the bus module reference count */
-	bus_module = phydev->bus->dev.driver ?
-		     phydev->bus->dev.driver->owner : NULL;
-	if (!try_module_get(bus_module)) {
-		dev_err(&dev->dev, "failed to get the bus module\n");
-		return -EIO;
+		err = -EBUSY;
+		goto error;
 	}
 
 	phydev->attached_dev = dev;
@@ -636,6 +634,10 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 		phy_resume(phydev);
 
 	return err;
+
+error:
+	module_put(bus->owner);
+	return err;
 }
 EXPORT_SYMBOL(phy_attach_direct);
 
@@ -680,11 +682,9 @@ EXPORT_SYMBOL(phy_attach);
  */
 void phy_detach(struct phy_device *phydev)
 {
+	struct mii_bus *bus;
 	int i;
 
-	if (phydev->bus->dev.driver)
-		module_put(phydev->bus->dev.driver->owner);
-
 	phydev->attached_dev->phydev = NULL;
 	phydev->attached_dev = NULL;
 	phy_suspend(phydev);
@@ -700,6 +700,10 @@ void phy_detach(struct phy_device *phydev)
 			break;
 		}
 	}
+
+	bus = phydev->bus;
+
+	module_put(bus->owner);
 }
 EXPORT_SYMBOL(phy_detach);
 
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 962387a192f1..11bce44f6d65 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -19,6 +19,7 @@
 #include <linux/spinlock.h>
 #include <linux/ethtool.h>
 #include <linux/mii.h>
+#include <linux/module.h>
 #include <linux/timer.h>
 #include <linux/workqueue.h>
 #include <linux/mod_devicetable.h>
@@ -153,6 +154,7 @@ struct sk_buff;
  * PHYs should register using this structure
  */
 struct mii_bus {
+	struct module *owner;
 	const char *name;
 	char id[MII_BUS_ID_SIZE];
 	void *priv;
@@ -198,7 +200,8 @@ static inline struct mii_bus *mdiobus_alloc(void)
 	return mdiobus_alloc_size(0);
 }
 
-int mdiobus_register(struct mii_bus *bus);
+int __mdiobus_register(struct mii_bus *bus, struct module *owner);
+#define mdiobus_register(bus) __mdiobus_register(bus, THIS_MODULE)
 void mdiobus_unregister(struct mii_bus *bus);
 void mdiobus_free(struct mii_bus *bus);
 struct mii_bus *devm_mdiobus_alloc_size(struct device *dev, int sizeof_priv);
-- 
2.1.0

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Thread

[PATCH v2 0/9] Phy, mdiobus, and netdev struct device fixes Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 8/9] phy: add phy_device_remove() Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 5/9] of_mdio: fix MDIO phy device refcounting Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 6/9] net: fix phy refcounting in a bunch of drivers Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 9/9] net: fix net_device refcounting Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 2/9] net: dsa: fix of_mdio_find_bus() device refcount leak Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 3/9] phy: fix mdiobus module safety Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  [PATCH 4/9] phy: add proper phy struct device refcounting Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-22 18:20 +0200
  Re: [PATCH v2 0/9] Phy, mdiobus, and netdev struct device fixes David Miller <davem@davemloft.net> - 2015-09-24 01:30 +0200
    Re: [PATCH v2 0/9] Phy, mdiobus, and netdev struct device fixes Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-09-24 18:10 +0200
  [PATCH RESEND v3 2/9] net: dsa: fix of_mdio_find_bus() device  refcount leak Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 7/9] phy: fixed-phy: properly validate phy in  fixed_phy_update_state() Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 5/9] of_mdio: fix MDIO phy device refcounting Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
    Re: [PATCH RESEND v3 5/9] of_mdio: fix MDIO phy device refcounting Rob Herring <robh@kernel.org> - 2015-09-25 00:30 +0200
  [PATCH RESEND v3 4/9] phy: add proper phy struct device refcounting Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 8/9] phy: add phy_device_remove() Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 1/9] phy: fix of_mdio_find_bus() device refcount  leak Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 6/9] net: fix phy refcounting in a bunch of drivers Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 3/9] phy: fix mdiobus module safety Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:40 +0200
  [PATCH RESEND v3 9/9] net: fix net_device refcounting Russell King <rmk+kernel@arm.linux.org.uk> - 2015-09-24 21:50 +0200

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