[AF_UNIX]: Use spinlock for unix_table_lock

This lock is actually taken mostly as a writer,
so using a rwlock actually just makes performance
worse especially on chips like the Intel P4.

Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/af_unix.h

@@ -13,7 +13,7 @@ extern void unix_gc(void);
 #define UNIX_HASH_SIZE	256
 
 extern struct hlist_head unix_socket_table[UNIX_HASH_SIZE + 1];
-extern rwlock_t unix_table_lock;
+extern spinlock_t unix_table_lock;
 
 extern atomic_t unix_tot_inflight;
 

net/unix/af_unix.c

@@ -121,7 +121,7 @@
 int sysctl_unix_max_dgram_qlen = 10;
 
 struct hlist_head unix_socket_table[UNIX_HASH_SIZE + 1];
-DEFINE_RWLOCK(unix_table_lock);
+DEFINE_SPINLOCK(unix_table_lock);
 static atomic_t unix_nr_socks = ATOMIC_INIT(0);
 
 #define unix_sockets_unbound	(&unix_socket_table[UNIX_HASH_SIZE])
@@ -130,7 +130,7 @@ static atomic_t unix_nr_socks = ATOMIC_INIT(0);
 
 /*
  *  SMP locking strategy:
- *    hash table is protected with rwlock unix_table_lock
+ *    hash table is protected with spinlock unix_table_lock
  *    each socket state is protected by separate rwlock.
  */
 
@@ -214,16 +214,16 @@ static void __unix_insert_socket(struct hlist_head *list, struct sock *sk)
 
 static inline void unix_remove_socket(struct sock *sk)
 {
-	write_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 	__unix_remove_socket(sk);
-	write_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 }
 
 static inline void unix_insert_socket(struct hlist_head *list, struct sock *sk)
 {
-	write_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 	__unix_insert_socket(list, sk);
-	write_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 }
 
 static struct sock *__unix_find_socket_byname(struct sockaddr_un *sunname,
@@ -250,11 +250,11 @@ static inline struct sock *unix_find_socket_byname(struct sockaddr_un *sunname,
 {
 	struct sock *s;
 
-	read_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 	s = __unix_find_socket_byname(sunname, len, type, hash);
 	if (s)
 		sock_hold(s);
-	read_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 	return s;
 }
 
@@ -263,7 +263,7 @@ static struct sock *unix_find_socket_byinode(struct inode *i)
 	struct sock *s;
 	struct hlist_node *node;
 
-	read_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 	sk_for_each(s, node,
 		    &unix_socket_table[i->i_ino & (UNIX_HASH_SIZE - 1)]) {
 		struct dentry *dentry = unix_sk(s)->dentry;
@@ -276,7 +276,7 @@ static struct sock *unix_find_socket_byinode(struct inode *i)
 	}
 	s = NULL;
 found:
-	read_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 	return s;
 }
 
@@ -642,12 +642,12 @@ retry:
 	addr->len = sprintf(addr->name->sun_path+1, "%05x", ordernum) + 1 + sizeof(short);
 	addr->hash = unix_hash_fold(csum_partial((void*)addr->name, addr->len, 0));
 
-	write_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 	ordernum = (ordernum+1)&0xFFFFF;
 
 	if (__unix_find_socket_byname(addr->name, addr->len, sock->type,
 				      addr->hash)) {
-		write_unlock(&unix_table_lock);
+		spin_unlock(&unix_table_lock);
 		/* Sanity yield. It is unusual case, but yet... */
 		if (!(ordernum&0xFF))
 			yield();
@@ -658,7 +658,7 @@ retry:
 	__unix_remove_socket(sk);
 	u->addr = addr;
 	__unix_insert_socket(&unix_socket_table[addr->hash], sk);
-	write_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 	err = 0;
 
 out:	up(&u->readsem);
@@ -791,7 +791,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		addr->hash = UNIX_HASH_SIZE;
 	}
 
-	write_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 
 	if (!sunaddr->sun_path[0]) {
 		err = -EADDRINUSE;
@@ -814,7 +814,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	__unix_insert_socket(list, sk);
 
 out_unlock:
-	write_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 out_up:
 	up(&u->readsem);
 out:
@@ -1916,7 +1916,7 @@ static struct sock *unix_seq_idx(int *iter, loff_t pos)
 
 static void *unix_seq_start(struct seq_file *seq, loff_t *pos)
 {
-	read_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 	return *pos ? unix_seq_idx(seq->private, *pos - 1) : ((void *) 1);
 }
 
@@ -1931,7 +1931,7 @@ static void *unix_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 static void unix_seq_stop(struct seq_file *seq, void *v)
 {
-	read_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 }
 
 static int unix_seq_show(struct seq_file *seq, void *v)

net/unix/garbage.c

@@ -182,7 +182,7 @@ void unix_gc(void)
 	if (down_trylock(&unix_gc_sem))
 		return;
 
-	read_lock(&unix_table_lock);
+	spin_lock(&unix_table_lock);
 
 	forall_unix_sockets(i, s)
 	{
@@ -301,7 +301,7 @@ void unix_gc(void)
 		}
 		u->gc_tree = GC_ORPHAN;
 	}
-	read_unlock(&unix_table_lock);
+	spin_unlock(&unix_table_lock);
 
 	/*
 	 *	Here we are. Hitlist is filled. Die.