[PATCH net-next 1/2] appletalk: stop storing per-interface state in struct net_device

[Jakub Kicinski <kuba@kernel.org>]

AppleTalk keeps its per-interface control block (struct atalk_iface)
directly in struct netdevice (dev->atalk_ptr). This is the only thing
tying the protocol into the core net_device layout and is the sole
blocker to moving AppleTalk out of tree.

Replace dev->atalk_ptr with a small ifindex-keyed hashtable internal
to ddp.c. The existing atalk_interfaces list stays the owner of the iface
objects; the hashtable is purely a fast dev->iface index and reuses
the same atalk_interfaces_lock.

AFAICT this patch does not make this code any more racy than it already
is, I'm sure Sashiko will point out some basically existing bugs.
AFAICT atalk_interfaces_lock is the innermost lock already.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 .../networking/net_cachelines/net_device.rst  |  1 -
 include/linux/atalk.h                         |  8 +---
 include/linux/netdevice.h                     |  4 --
 net/appletalk/ddp.c                           | 48 +++++++++++++++++--
 4 files changed, 45 insertions(+), 16 deletions(-)

diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
index eb2e6851c6f6..512f6d6fa3d8 100644
--- a/Documentation/networking/net_cachelines/net_device.rst
+++ b/Documentation/networking/net_cachelines/net_device.rst
@@ -90,7 +90,6 @@ struct inet6_dev*                   ip6_ptr                     read_mostly
 struct vlan_info*                   vlan_info
 struct dsa_port*                    dsa_ptr
 struct tipc_bearer*                 tipc_ptr
-void*                               atalk_ptr
 struct wireless_dev*                ieee80211_ptr
 struct wpan_dev*                    ieee802154_ptr
 struct mpls_dev*                    mpls_ptr
diff --git a/include/linux/atalk.h b/include/linux/atalk.h
index a55bfc6567d0..ce7e6bfa9e2a 100644
--- a/include/linux/atalk.h
+++ b/include/linux/atalk.h
@@ -30,6 +30,7 @@ struct atalk_iface {
 #define ATIF_PROBE_FAIL	2		/* Probe collided */
 	struct atalk_netrange	nets;
 	struct atalk_iface	*next;
+	struct hlist_node	hash_node;	/* keyed on dev->ifindex */
 };
 	
 struct atalk_sock {
@@ -113,12 +114,7 @@ extern int aarp_proto_init(void);
 /* Inter module exports */
 
 /* Give a device find its atif control structure */
-#if IS_ENABLED(CONFIG_ATALK)
-static inline struct atalk_iface *atalk_find_dev(struct net_device *dev)
-{
-	return dev->atalk_ptr;
-}
-#endif
+extern struct atalk_iface *atalk_find_dev(struct net_device *dev);
 
 extern struct atalk_addr *atalk_find_dev_addr(struct net_device *dev);
 extern struct net_device *atrtr_get_dev(struct atalk_addr *sa);
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 7f4f0837c09f..655564621f28 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1947,7 +1947,6 @@ enum netdev_reg_state {
  *	@vlan_info:	VLAN info
  *	@dsa_ptr:	dsa specific data
  *	@tipc_ptr:	TIPC specific data
- *	@atalk_ptr:	AppleTalk link
  *	@ip_ptr:	IPv4 specific data
  *	@ip6_ptr:	IPv6 specific data
  *	@ieee80211_ptr:	IEEE 802.11 specific data, assign before registering
@@ -2349,9 +2348,6 @@ struct net_device {
 #if IS_ENABLED(CONFIG_TIPC)
 	struct tipc_bearer __rcu *tipc_ptr;
 #endif
-#if IS_ENABLED(CONFIG_ATALK)
-	void 			*atalk_ptr;
-#endif
 #if IS_ENABLED(CONFIG_CFG80211)
 	struct wireless_dev	*ieee80211_ptr;
 #endif
diff --git a/net/appletalk/ddp.c b/net/appletalk/ddp.c
index 30a6dc06291c..afb86ce6e644 100644
--- a/net/appletalk/ddp.c
+++ b/net/appletalk/ddp.c
@@ -52,6 +52,7 @@
 #include <linux/termios.h>	/* For TIOCOUTQ/INQ */
 #include <linux/compat.h>
 #include <linux/slab.h>
+#include <linux/hashtable.h>
 #include <net/datalink.h>
 #include <net/psnap.h>
 #include <net/sock.h>
@@ -204,6 +205,33 @@ DEFINE_RWLOCK(atalk_routes_lock);
 struct atalk_iface *atalk_interfaces;
 DEFINE_RWLOCK(atalk_interfaces_lock);
 
+/* Fast dev->iface lookup, keyed on ifindex. Shares atalk_interfaces_lock with
+ * the atalk_interfaces list, which remains the owner of the iface objects.
+ */
+#define ATALK_IFACE_HASH_BITS	8
+static DEFINE_HASHTABLE(atalk_iface_hash, ATALK_IFACE_HASH_BITS);
+
+/* Find the iface for @dev. Caller must hold atalk_interfaces_lock. */
+static struct atalk_iface *__atalk_find_dev(struct net_device *dev)
+{
+	struct atalk_iface *iface;
+
+	hash_for_each_possible(atalk_iface_hash, iface, hash_node, dev->ifindex)
+		if (iface->dev == dev)
+			return iface;
+	return NULL;
+}
+
+struct atalk_iface *atalk_find_dev(struct net_device *dev)
+{
+	struct atalk_iface *iface;
+
+	read_lock_bh(&atalk_interfaces_lock);
+	iface = __atalk_find_dev(dev);
+	read_unlock_bh(&atalk_interfaces_lock);
+	return iface;
+}
+
 /* For probing devices or in a routerless network */
 struct atalk_route atrtr_default;
 
@@ -221,9 +249,9 @@ static void atif_drop_device(struct net_device *dev)
 	while ((tmp = *iface) != NULL) {
 		if (tmp->dev == dev) {
 			*iface = tmp->next;
+			hash_del(&tmp->hash_node);
 			dev_put(dev);
 			kfree(tmp);
-			dev->atalk_ptr = NULL;
 		} else
 			iface = &tmp->next;
 	}
@@ -240,13 +268,13 @@ static struct atalk_iface *atif_add_device(struct net_device *dev,
 
 	dev_hold(dev);
 	iface->dev = dev;
-	dev->atalk_ptr = iface;
 	iface->address = *sa;
 	iface->status = 0;
 
 	write_lock_bh(&atalk_interfaces_lock);
 	iface->next = atalk_interfaces;
 	atalk_interfaces = iface;
+	hash_add(atalk_iface_hash, &iface->hash_node, dev->ifindex);
 	write_unlock_bh(&atalk_interfaces_lock);
 out:
 	return iface;
@@ -347,8 +375,15 @@ static int atif_proxy_probe_device(struct atalk_iface *atif,
 
 struct atalk_addr *atalk_find_dev_addr(struct net_device *dev)
 {
-	struct atalk_iface *iface = dev->atalk_ptr;
-	return iface ? &iface->address : NULL;
+	struct atalk_addr *addr = NULL;
+	struct atalk_iface *iface;
+
+	read_lock_bh(&atalk_interfaces_lock);
+	iface = __atalk_find_dev(dev);
+	if (iface)
+		addr = &iface->address;
+	read_unlock_bh(&atalk_interfaces_lock);
+	return addr;
 }
 
 static struct atalk_addr *atalk_find_primary(void)
@@ -388,8 +423,10 @@ static struct atalk_addr *atalk_find_primary(void)
  */
 static struct atalk_iface *atalk_find_anynet(int node, struct net_device *dev)
 {
-	struct atalk_iface *iface = dev->atalk_ptr;
+	struct atalk_iface *iface;
 
+	read_lock_bh(&atalk_interfaces_lock);
+	iface = __atalk_find_dev(dev);
 	if (!iface || iface->status & ATIF_PROBE)
 		goto out_err;
 
@@ -398,6 +435,7 @@ static struct atalk_iface *atalk_find_anynet(int node, struct net_device *dev)
 	    node != ATADDR_ANYNODE)
 		goto out_err;
 out:
+	read_unlock_bh(&atalk_interfaces_lock);
 	return iface;
 out_err:
 	iface = NULL;
-- 
2.54.0