netdev - [PATCH v3 net-next 13/13] net: remove dev_base

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Date: Fri,  9 Feb 2024 20:34:28 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v3 net-next 13/13] net: remove dev_base_lock

dev_base_lock is not needed anymore, all remaining users also hold RTNL.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/netdevice.h |  2 --
 net/core/dev.c            | 39 ++++-----------------------------------
 2 files changed, 4 insertions(+), 37 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d4d1e438ab8f1d2bd6426837b504ad6891fe83b7..94968baa7da172b69cc8ac148d39315018893420 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3077,8 +3077,6 @@ int call_netdevice_notifiers(unsigned long val, struct net_device *dev);
 int call_netdevice_notifiers_info(unsigned long val,
 				  struct netdev_notifier_info *info);
 
-extern rwlock_t				dev_base_lock;		/* Device list lock */
-
 #define for_each_netdev(net, d)		\
 		list_for_each_entry(d, &(net)->dev_base_head, dev_list)
 #define for_each_netdev_reverse(net, d)	\
diff --git a/net/core/dev.c b/net/core/dev.c
index a1cb7d3cab2c521fc28bd5f522c147bffca8d15e..456877e4b5d165878b3886db56d934c9e8c9cedc 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -166,28 +166,6 @@ static int call_netdevice_notifiers_extack(unsigned long val,
 					   struct net_device *dev,
 					   struct netlink_ext_ack *extack);
 
-/*
- * The @dev_base_head list is protected by @dev_base_lock and the rtnl
- * semaphore.
- *
- * Pure readers hold dev_base_lock for reading, or rcu_read_lock()
- *
- * Writers must hold the rtnl semaphore while they loop through the
- * dev_base_head list, and hold dev_base_lock for writing when they do the
- * actual updates.  This allows pure readers to access the list even
- * while a writer is preparing to update it.
- *
- * To put it another way, dev_base_lock is held for writing only to
- * protect against pure readers; the rtnl semaphore provides the
- * protection against other writers.
- *
- * See, for example usages, register_netdevice() and
- * unregister_netdevice(), which must be called with the rtnl
- * semaphore held.
- */
-DEFINE_RWLOCK(dev_base_lock);
-EXPORT_SYMBOL(dev_base_lock);
-
 static DEFINE_MUTEX(ifalias_mutex);
 
 /* protects napi_hash addition/deletion and napi_gen_id */
@@ -393,12 +371,10 @@ static void list_netdevice(struct net_device *dev)
 
 	ASSERT_RTNL();
 
-	write_lock(&dev_base_lock);
 	list_add_tail_rcu(&dev->dev_list, &net->dev_base_head);
 	netdev_name_node_add(net, dev->name_node);
 	hlist_add_head_rcu(&dev->index_hlist,
 			   dev_index_hash(net, dev->ifindex));
-	write_unlock(&dev_base_lock);
 
 	netdev_for_each_altname(dev, name_node)
 		netdev_name_node_add(net, name_node);
@@ -425,11 +401,9 @@ static void unlist_netdevice(struct net_device *dev)
 		netdev_name_node_del(name_node);
 
 	/* Unlink dev from the device chain */
-	write_lock(&dev_base_lock);
 	list_del_rcu(&dev->dev_list);
 	netdev_name_node_del(dev->name_node);
 	hlist_del_rcu(&dev->index_hlist);
-	write_unlock(&dev_base_lock);
 
 	dev_base_seq_inc(dev_net(dev));
 }
@@ -744,9 +718,9 @@ EXPORT_SYMBOL_GPL(dev_fill_forward_path);
  *	@net: the applicable net namespace
  *	@name: name to find
  *
- *	Find an interface by name. Must be called under RTNL semaphore
- *	or @dev_base_lock. If the name is found a pointer to the device
- *	is returned. If the name is not found then %NULL is returned. The
+ *	Find an interface by name. Must be called under RTNL semaphore.
+ *	If the name is found a pointer to the device is returned.
+ *	If the name is not found then %NULL is returned. The
  *	reference counters are not incremented so the caller must be
  *	careful with locks.
  */
@@ -827,8 +801,7 @@ EXPORT_SYMBOL(netdev_get_by_name);
  *	Search for an interface by index. Returns %NULL if the device
  *	is not found or a pointer to the device. The device has not
  *	had its reference counter increased so the caller must be careful
- *	about locking. The caller must hold either the RTNL semaphore
- *	or @dev_base_lock.
+ *	about locking. The caller must hold the RTNL semaphore.
  */
 
 struct net_device *__dev_get_by_index(struct net *net, int ifindex)
@@ -1233,15 +1206,11 @@ int dev_change_name(struct net_device *dev, const char *newname)
 
 	netdev_adjacent_rename_links(dev, oldname);
 
-	write_lock(&dev_base_lock);
 	netdev_name_node_del(dev->name_node);
-	write_unlock(&dev_base_lock);
 
 	synchronize_rcu();
 
-	write_lock(&dev_base_lock);
 	netdev_name_node_add(net, dev->name_node);
-	write_unlock(&dev_base_lock);
 
 	ret = call_netdevice_notifiers(NETDEV_CHANGENAME, dev);
 	ret = notifier_to_errno(ret);
-- 
2.43.0.687.g38aa6559b0-goog