net: annotate data-races around sk->sk_forward_alloc

Every time sk->sk_forward_alloc is read locklessly,
add a READ_ONCE().

Add sk_forward_alloc_add() helper to centralize updates,
to reduce number of WRITE_ONCE().

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1053,6 +1053,12 @@ static inline void sk_wmem_queued_add(struct sock *sk, int val)
 	WRITE_ONCE(sk->sk_wmem_queued, sk->sk_wmem_queued + val);
 }
 
+static inline void sk_forward_alloc_add(struct sock *sk, int val)
+{
+	/* Paired with lockless reads of sk->sk_forward_alloc */
+	WRITE_ONCE(sk->sk_forward_alloc, sk->sk_forward_alloc + val);
+}
+
 void sk_stream_write_space(struct sock *sk);
 
 /* OOB backlog add */
@@ -1377,7 +1383,7 @@ static inline int sk_forward_alloc_get(const struct sock *sk)
 	if (sk->sk_prot->forward_alloc_get)
 		return sk->sk_prot->forward_alloc_get(sk);
 #endif
-	return sk->sk_forward_alloc;
+	return READ_ONCE(sk->sk_forward_alloc);
 }
 
 static inline bool __sk_stream_memory_free(const struct sock *sk, int wake)
@@ -1673,14 +1679,14 @@ static inline void sk_mem_charge(struct sock *sk, int size)
 {
 	if (!sk_has_account(sk))
 		return;
-	sk->sk_forward_alloc -= size;
+	sk_forward_alloc_add(sk, -size);
 }
 
 static inline void sk_mem_uncharge(struct sock *sk, int size)
 {
 	if (!sk_has_account(sk))
 		return;
-	sk->sk_forward_alloc += size;
+	sk_forward_alloc_add(sk, size);
 	sk_mem_reclaim(sk);
 }
 

net/core/sock.c

@@ -1045,7 +1045,7 @@ static int sock_reserve_memory(struct sock *sk, int bytes)
 		mem_cgroup_uncharge_skmem(sk->sk_memcg, pages);
 		return -ENOMEM;
 	}
-	sk->sk_forward_alloc += pages << PAGE_SHIFT;
+	sk_forward_alloc_add(sk, pages << PAGE_SHIFT);
 
 	WRITE_ONCE(sk->sk_reserved_mem,
 		   sk->sk_reserved_mem + (pages << PAGE_SHIFT));
@@ -3139,10 +3139,10 @@ int __sk_mem_schedule(struct sock *sk, int size, int kind)
 {
 	int ret, amt = sk_mem_pages(size);
 
-	sk->sk_forward_alloc += amt << PAGE_SHIFT;
+	sk_forward_alloc_add(sk, amt << PAGE_SHIFT);
 	ret = __sk_mem_raise_allocated(sk, size, amt, kind);
 	if (!ret)
-		sk->sk_forward_alloc -= amt << PAGE_SHIFT;
+		sk_forward_alloc_add(sk, -(amt << PAGE_SHIFT));
 	return ret;
 }
 EXPORT_SYMBOL(__sk_mem_schedule);
@@ -3174,7 +3174,7 @@ void __sk_mem_reduce_allocated(struct sock *sk, int amount)
 void __sk_mem_reclaim(struct sock *sk, int amount)
 {
 	amount >>= PAGE_SHIFT;
-	sk->sk_forward_alloc -= amount << PAGE_SHIFT;
+	sk_forward_alloc_add(sk, -(amount << PAGE_SHIFT));
 	__sk_mem_reduce_allocated(sk, amount);
 }
 EXPORT_SYMBOL(__sk_mem_reclaim);

net/ipv4/tcp_output.c

@@ -3474,7 +3474,7 @@ void sk_forced_mem_schedule(struct sock *sk, int size)
 	if (delta <= 0)
 		return;
 	amt = sk_mem_pages(delta);
-	sk->sk_forward_alloc += amt << PAGE_SHIFT;
+	sk_forward_alloc_add(sk, amt << PAGE_SHIFT);
 	sk_memory_allocated_add(sk, amt);
 
 	if (mem_cgroup_sockets_enabled && sk->sk_memcg)

net/ipv4/udp.c

@@ -1414,9 +1414,9 @@ static void udp_rmem_release(struct sock *sk, int size, int partial,
 		spin_lock(&sk_queue->lock);
 
 
-	sk->sk_forward_alloc += size;
+	sk_forward_alloc_add(sk, size);
 	amt = (sk->sk_forward_alloc - partial) & ~(PAGE_SIZE - 1);
-	sk->sk_forward_alloc -= amt;
+	sk_forward_alloc_add(sk, -amt);
 
 	if (amt)
 		__sk_mem_reduce_allocated(sk, amt >> PAGE_SHIFT);
@@ -1527,7 +1527,7 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 		goto uncharge_drop;
 	}
 
-	sk->sk_forward_alloc -= size;
+	sk_forward_alloc_add(sk, -size);
 
 	/* no need to setup a destructor, we will explicitly release the
 	 * forward allocated memory on dequeue

net/mptcp/protocol.c

@@ -1800,7 +1800,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		}
 
 		/* data successfully copied into the write queue */
-		sk->sk_forward_alloc -= total_ts;
+		sk_forward_alloc_add(sk, -total_ts);
 		copied += psize;
 		dfrag->data_len += psize;
 		frag_truesize += psize;
@@ -3257,7 +3257,7 @@ void mptcp_destroy_common(struct mptcp_sock *msk, unsigned int flags)
 	/* move all the rx fwd alloc into the sk_mem_reclaim_final in
 	 * inet_sock_destruct() will dispose it
 	 */
-	sk->sk_forward_alloc += msk->rmem_fwd_alloc;
+	sk_forward_alloc_add(sk, msk->rmem_fwd_alloc);
 	msk->rmem_fwd_alloc = 0;
 	mptcp_token_destroy(msk);
 	mptcp_pm_free_anno_list(msk);
@@ -3522,7 +3522,7 @@ static void mptcp_shutdown(struct sock *sk, int how)
 
 static int mptcp_forward_alloc_get(const struct sock *sk)
 {
-	return sk->sk_forward_alloc + mptcp_sk(sk)->rmem_fwd_alloc;
+	return READ_ONCE(sk->sk_forward_alloc) + mptcp_sk(sk)->rmem_fwd_alloc;
 }
 
 static int mptcp_ioctl_outq(const struct mptcp_sock *msk, u64 v)