mptcp: annotate data-races around msk->rmem_fwd_alloc

msk->rmem_fwd_alloc can be read locklessly.

Add mptcp_rmem_fwd_alloc_add(), similar to sk_forward_alloc_add(),
and appropriate READ_ONCE()/WRITE_ONCE() annotations.

Fixes: 6511882 ("mptcp: allocate fwd memory separately on the rx and tx path")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/protocol.c

@@ -134,9 +134,15 @@ static void mptcp_drop(struct sock *sk, struct sk_buff *skb)
 	__kfree_skb(skb);
 }
 
+static void mptcp_rmem_fwd_alloc_add(struct sock *sk, int size)
+{
+	WRITE_ONCE(mptcp_sk(sk)->rmem_fwd_alloc,
+		   mptcp_sk(sk)->rmem_fwd_alloc + size);
+}
+
 static void mptcp_rmem_charge(struct sock *sk, int size)
 {
-	mptcp_sk(sk)->rmem_fwd_alloc -= size;
+	mptcp_rmem_fwd_alloc_add(sk, -size);
 }
 
 static bool mptcp_try_coalesce(struct sock *sk, struct sk_buff *to,
@@ -177,7 +183,7 @@ static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to,
 static void __mptcp_rmem_reclaim(struct sock *sk, int amount)
 {
 	amount >>= PAGE_SHIFT;
-	mptcp_sk(sk)->rmem_fwd_alloc -= amount << PAGE_SHIFT;
+	mptcp_rmem_charge(sk, amount << PAGE_SHIFT);
 	__sk_mem_reduce_allocated(sk, amount);
 }
 
@@ -186,7 +192,7 @@ static void mptcp_rmem_uncharge(struct sock *sk, int size)
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	int reclaimable;
 
-	msk->rmem_fwd_alloc += size;
+	mptcp_rmem_fwd_alloc_add(sk, size);
 	reclaimable = msk->rmem_fwd_alloc - sk_unused_reserved_mem(sk);
 
 	/* see sk_mem_uncharge() for the rationale behind the following schema */
@@ -341,7 +347,7 @@ static bool mptcp_rmem_schedule(struct sock *sk, struct sock *ssk, int size)
 	if (!__sk_mem_raise_allocated(sk, size, amt, SK_MEM_RECV))
 		return false;
 
-	msk->rmem_fwd_alloc += amount;
+	mptcp_rmem_fwd_alloc_add(sk, amount);
 	return true;
 }
 
@@ -3258,7 +3264,7 @@ void mptcp_destroy_common(struct mptcp_sock *msk, unsigned int flags)
 	 * inet_sock_destruct() will dispose it
 	 */
 	sk_forward_alloc_add(sk, msk->rmem_fwd_alloc);
-	msk->rmem_fwd_alloc = 0;
+	WRITE_ONCE(msk->rmem_fwd_alloc, 0);
 	mptcp_token_destroy(msk);
 	mptcp_pm_free_anno_list(msk);
 	mptcp_free_local_addr_list(msk);
@@ -3522,7 +3528,8 @@ static void mptcp_shutdown(struct sock *sk, int how)
 
 static int mptcp_forward_alloc_get(const struct sock *sk)
 {
-	return READ_ONCE(sk->sk_forward_alloc) + mptcp_sk(sk)->rmem_fwd_alloc;
+	return READ_ONCE(sk->sk_forward_alloc) +
+	       READ_ONCE(mptcp_sk(sk)->rmem_fwd_alloc);
 }
 
 static int mptcp_ioctl_outq(const struct mptcp_sock *msk, u64 v)