net: listening_hash get a spinlock per bucket

This patch prepares RCU migration of listening_hash table for
TCP/DCCP protocols.

listening_hash table being small (32 slots per protocol), we add
a spinlock for each slot, instead of a single rwlock for whole table.

This should reduce hold time of readers, and writers concurrency.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 30 deletions

diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index 481896045111..62d2dd0d7860 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -99,6 +99,11 @@ struct inet_bind_hashbucket {
         struct hlist_head       chain;
 };
 
+struct inet_listen_hashbucket {
+        spinlock_t              lock;
+        struct hlist_head       head;
+};
+
 /* This is for listening sockets, thus all sockets which possess wildcards. */
 #define INET_LHTABLE_SIZE       32      /* Yes, really, this is all you need. */
 
@@ -123,22 +128,21 @@ struct inet_hashinfo {
         unsigned int                    bhash_size;
         /* Note : 4 bytes padding on 64 bit arches */
 
-        /* All sockets in TCP_LISTEN state will be in here.  This is the only
-         * table where wildcard'd TCP sockets can exist.  Hash function here
-         * is just local port number.
-         */
-        struct hlist_head               listening_hash[INET_LHTABLE_SIZE];
+        struct kmem_cache               *bind_bucket_cachep;
 
         /* All the above members are written once at bootup and
          * never written again _or_ are predominantly read-access.
          *
          * Now align to a new cache line as all the following members
-         * are often dirty.
+         * might be often dirty.
+         */
+        /* All sockets in TCP_LISTEN state will be in here.  This is the only
+         * table where wildcard'd TCP sockets can exist.  Hash function here
+         * is just local port number.
          */
-        rwlock_t                        lhash_lock ____cacheline_aligned;
-        atomic_t                        lhash_users;
-        wait_queue_head_t               lhash_wait;
-        struct kmem_cache                       *bind_bucket_cachep;
+        struct inet_listen_hashbucket   listening_hash[INET_LHTABLE_SIZE]
+                                        ____cacheline_aligned_in_smp;
+
 };
 
 static inline struct inet_ehash_bucket *inet_ehash_bucket(
@@ -236,26 +240,7 @@ extern void __inet_inherit_port(struct sock *sk, struct sock *child);
 
 extern void inet_put_port(struct sock *sk);
 
-extern void inet_listen_wlock(struct inet_hashinfo *hashinfo);
-
-/*
- * - We may sleep inside this lock.
- * - If sleeping is not required (or called from BH),
- *   use plain read_(un)lock(&inet_hashinfo.lhash_lock).
- */
-static inline void inet_listen_lock(struct inet_hashinfo *hashinfo)
-{
-        /* read_lock synchronizes to candidates to writers */
-        read_lock(&hashinfo->lhash_lock);
-        atomic_inc(&hashinfo->lhash_users);
-        read_unlock(&hashinfo->lhash_lock);
-}
-
-static inline void inet_listen_unlock(struct inet_hashinfo *hashinfo)
-{
-        if (atomic_dec_and_test(&hashinfo->lhash_users))
-                wake_up(&hashinfo->lhash_wait);
-}
+void inet_hashinfo_init(struct inet_hashinfo *h);
 
 extern void __inet_hash_nolisten(struct sock *sk);
 extern void inet_hash(struct sock *sk);