net: sk_wmem_alloc has initial value of one, not zero

commit 2b85a34e911bf483c27cfdd124aeb1605145dc80
(net: No more expensive sock_hold()/sock_put() on each tx)
changed initial sk_wmem_alloc value.

Some protocols check sk_wmem_alloc value to determine if a timer
must delay socket deallocation. We must take care of the sk_wmem_alloc
value being one instead of zero when no write allocations are pending.

Reported by Ingo Molnar, and full diagnostic from David Miller.

This patch introduces three helpers to get read/write allocations
and a followup patch will use these helpers to report correct
write allocations to user.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1206,6 +1206,39 @@ static inline int skb_copy_to_page(struct sock *sk, char __user *from,
 	return 0;
 }
 
+/**
+ * sk_wmem_alloc_get - returns write allocations
+ * @sk: socket
+ *
+ * Returns sk_wmem_alloc minus initial offset of one
+ */
+static inline int sk_wmem_alloc_get(const struct sock *sk)
+{
+	return atomic_read(&sk->sk_wmem_alloc) - 1;
+}
+
+/**
+ * sk_rmem_alloc_get - returns read allocations
+ * @sk: socket
+ *
+ * Returns sk_rmem_alloc
+ */
+static inline int sk_rmem_alloc_get(const struct sock *sk)
+{
+	return atomic_read(&sk->sk_rmem_alloc);
+}
+
+/**
+ * sk_has_allocations - check if allocations are outstanding
+ * @sk: socket
+ *
+ * Returns true if socket has write or read allocations
+ */
+static inline int sk_has_allocations(const struct sock *sk)
+{
+	return sk_wmem_alloc_get(sk) || sk_rmem_alloc_get(sk);
+}
+
 /*
  * 	Queue a received datagram if it will fit. Stream and sequenced
  *	protocols can't normally use this as they need to fit buffers in

net/appletalk/ddp.c

@@ -162,8 +162,7 @@ static void atalk_destroy_timer(unsigned long data)
 {
 	struct sock *sk = (struct sock *)data;
 
-	if (atomic_read(&sk->sk_wmem_alloc) ||
-	    atomic_read(&sk->sk_rmem_alloc)) {
+	if (sk_has_allocations(sk)) {
 		sk->sk_timer.expires = jiffies + SOCK_DESTROY_TIME;
 		add_timer(&sk->sk_timer);
 	} else
@@ -175,8 +174,7 @@ static inline void atalk_destroy_socket(struct sock *sk)
 	atalk_remove_socket(sk);
 	skb_queue_purge(&sk->sk_receive_queue);
 
-	if (atomic_read(&sk->sk_wmem_alloc) ||
-	    atomic_read(&sk->sk_rmem_alloc)) {
+	if (sk_has_allocations(sk)) {
 		setup_timer(&sk->sk_timer, atalk_destroy_timer,
 				(unsigned long)sk);
 		sk->sk_timer.expires	= jiffies + SOCK_DESTROY_TIME;

net/ax25/af_ax25.c

@@ -330,8 +330,7 @@ void ax25_destroy_socket(ax25_cb *ax25)
 	}
 
 	if (ax25->sk != NULL) {
-		if (atomic_read(&ax25->sk->sk_wmem_alloc) ||
-		    atomic_read(&ax25->sk->sk_rmem_alloc)) {
+		if (sk_has_allocations(ax25->sk)) {
 			/* Defer: outstanding buffers */
 			setup_timer(&ax25->dtimer, ax25_destroy_timer,
 					(unsigned long)ax25);

net/econet/af_econet.c

@@ -540,8 +540,7 @@ static void econet_destroy_timer(unsigned long data)
 {
 	struct sock *sk=(struct sock *)data;
 
-	if (!atomic_read(&sk->sk_wmem_alloc) &&
-	    !atomic_read(&sk->sk_rmem_alloc)) {
+	if (!sk_has_allocations(sk)) {
 		sk_free(sk);
 		return;
 	}
@@ -579,8 +578,7 @@ static int econet_release(struct socket *sock)
 
 	skb_queue_purge(&sk->sk_receive_queue);
 
-	if (atomic_read(&sk->sk_rmem_alloc) ||
-	    atomic_read(&sk->sk_wmem_alloc)) {
+	if (sk_has_allocations(sk)) {
 		sk->sk_timer.data     = (unsigned long)sk;
 		sk->sk_timer.expires  = jiffies + HZ;
 		sk->sk_timer.function = econet_destroy_timer;

net/netrom/af_netrom.c

@@ -286,8 +286,7 @@ void nr_destroy_socket(struct sock *sk)
 		kfree_skb(skb);
 	}
 
-	if (atomic_read(&sk->sk_wmem_alloc) ||
-	    atomic_read(&sk->sk_rmem_alloc)) {
+	if (sk_has_allocations(sk)) {
 		/* Defer: outstanding buffers */
 		sk->sk_timer.function = nr_destroy_timer;
 		sk->sk_timer.expires  = jiffies + 2 * HZ;

net/rose/af_rose.c

@@ -356,8 +356,7 @@ void rose_destroy_socket(struct sock *sk)
 		kfree_skb(skb);
 	}
 
-	if (atomic_read(&sk->sk_wmem_alloc) ||
-	    atomic_read(&sk->sk_rmem_alloc)) {
+	if (sk_has_allocations(sk)) {
 		/* Defer: outstanding buffers */
 		setup_timer(&sk->sk_timer, rose_destroy_timer,
 				(unsigned long)sk);

net/x25/af_x25.c

@@ -372,8 +372,7 @@ static void __x25_destroy_socket(struct sock *sk)
 		kfree_skb(skb);
 	}
 
-	if (atomic_read(&sk->sk_wmem_alloc) ||
-	    atomic_read(&sk->sk_rmem_alloc)) {
+	if (sk_has_allocations(sk)) {
 		/* Defer: outstanding buffers */
 		sk->sk_timer.expires  = jiffies + 10 * HZ;
 		sk->sk_timer.function = x25_destroy_timer;