@@ -92,6 +92,27 @@ static inline bool lockdep_rtnl_is_held(void)
#define rcu_replace_pointer_rtnl(rp, p) \
rcu_replace_pointer(rp, p, lockdep_rtnl_is_held())
+#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
+void __rtnl_net_lock(struct net *net);
+void __rtnl_net_unlock(struct net *net);
+void rtnl_net_lock(struct net *net);
+void rtnl_net_unlock(struct net *net);
+int rtnl_net_lock_cmp_fn(const struct lockdep_map *a, const struct lockdep_map *b);
+#else
+static inline void __rtnl_net_lock(struct net *net) {}
+static inline void __rtnl_net_unlock(struct net *net) {}
+
+static inline void rtnl_net_lock(struct net *net)
+{
+ rtnl_lock();
+}
+
+static inline void rtnl_net_unlock(struct net *net)
+{
+ rtnl_unlock();
+}
+#endif
+
static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev)
{
return rtnl_dereference(dev->ingress_queue);
@@ -188,6 +188,10 @@ struct net {
#if IS_ENABLED(CONFIG_SMC)
struct netns_smc smc;
#endif
+#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
+ /* Move to a better place when the config guard is removed. */
+ struct mutex rtnl_mutex;
+#endif
} __randomize_layout;
#include <linux/seq_file_net.h>
@@ -24,3 +24,18 @@ config DEBUG_NET
help
Enable extra sanity checks in networking.
This is mostly used by fuzzers, but is safe to select.
+
+config DEBUG_NET_SMALL_RTNL
+ bool "Add extra per-netns mutex inside RTNL"
+ depends on DEBUG_KERNEL && NET && LOCK_DEBUGGING_SUPPORT
+ select PROVE_LOCKING
+ default n
+ help
+ rtnl_lock() is being replaced with rtnl_net_lock() that
+ acquires the global RTNL and a small per-netns RTNL mutex.
+
+ During the conversion, rtnl_net_lock() just adds an extra
+ mutex in every RTNL scope and slows down the operations.
+
+ Once the conversion completes, rtnl_lock() will be removed
+ and rtnetlink will gain per-netns scalability.
@@ -334,6 +334,12 @@ static __net_init void preinit_net(struct net *net, struct user_namespace *user_
idr_init(&net->netns_ids);
spin_lock_init(&net->nsid_lock);
mutex_init(&net->ipv4.ra_mutex);
+
+#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
+ mutex_init(&net->rtnl_mutex);
+ lock_set_cmp_fn(&net->rtnl_mutex, rtnl_net_lock_cmp_fn, NULL);
+#endif
+
preinit_net_sysctl(net);
}
@@ -179,6 +179,64 @@ bool lockdep_rtnl_is_held(void)
EXPORT_SYMBOL(lockdep_rtnl_is_held);
#endif /* #ifdef CONFIG_PROVE_LOCKING */
+#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
+void __rtnl_net_lock(struct net *net)
+{
+ ASSERT_RTNL();
+
+ mutex_lock(&net->rtnl_mutex);
+}
+EXPORT_SYMBOL(__rtnl_net_lock);
+
+void __rtnl_net_unlock(struct net *net)
+{
+ ASSERT_RTNL();
+
+ mutex_unlock(&net->rtnl_mutex);
+}
+EXPORT_SYMBOL(__rtnl_net_unlock);
+
+void rtnl_net_lock(struct net *net)
+{
+ rtnl_lock();
+ __rtnl_net_lock(net);
+}
+EXPORT_SYMBOL(rtnl_net_lock);
+
+void rtnl_net_unlock(struct net *net)
+{
+ __rtnl_net_unlock(net);
+ rtnl_unlock();
+}
+EXPORT_SYMBOL(rtnl_net_unlock);
+
+static int rtnl_net_cmp_locks(const struct net *net_a, const struct net *net_b)
+{
+ if (net_eq(net_a, net_b))
+ return 0;
+
+ /* always init_net first */
+ if (net_eq(net_a, &init_net))
+ return -1;
+
+ if (net_eq(net_b, &init_net))
+ return 1;
+
+ /* otherwise lock in ascending order */
+ return net_a < net_b ? -1 : 1;
+}
+
+int rtnl_net_lock_cmp_fn(const struct lockdep_map *a, const struct lockdep_map *b)
+{
+ const struct net *net_a, *net_b;
+
+ net_a = container_of(a, struct net, rtnl_mutex.dep_map);
+ net_b = container_of(b, struct net, rtnl_mutex.dep_map);
+
+ return rtnl_net_cmp_locks(net_a, net_b);
+}
+#endif
+
static struct rtnl_link __rcu *__rcu *rtnl_msg_handlers[RTNL_FAMILY_MAX + 1];
static inline int rtm_msgindex(int msgtype)
The goal is to break RTNL down into per-netns mutex. This patch adds per-netns mutex and its helper functions, rtnl_net_lock() and rtnl_net_unlock(). rtnl_net_lock() acquires the global RTNL and per-netns RTNL mutex, and rtnl_net_unlock() releases them. We will replace 800+ rtnl_lock() with rtnl_net_lock() and finally removes rtnl_lock() in rtnl_net_lock(). When we need to nest per-netns RTNL mutex, we will use __rtnl_net_lock(), and its locking order is defined by rtnl_net_lock_cmp_fn() as follows: 1. init_net is first 2. netns address ascending order Note that the conversion will be done under CONFIG_DEBUG_NET_SMALL_RTNL with LOCKDEP so that we can carefully add the extra mutex without slowing down RTNL operations during conversion. Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> --- include/linux/rtnetlink.h | 21 ++++++++++++++ include/net/net_namespace.h | 4 +++ net/Kconfig.debug | 15 ++++++++++ net/core/net_namespace.c | 6 ++++ net/core/rtnetlink.c | 58 +++++++++++++++++++++++++++++++++++++ 5 files changed, 104 insertions(+)