Merge branch 'remove-sk-skb-caches'

Paolo Abeni says:

====================
net: remove sk skb caches

Eric noted we would be better off reverting the sk
skb caches.

MPTCP relies on such a feature, so we need a
little refactor of the MPTCP tx path before the mentioned
revert.

The first patch exposes additional TCP helpers. The 2nd patch
changes the MPTCP code to do locally the whole skb allocation
and updating, so it does not rely anymore on core TCP helpers
for that nor the sk skb cache.

As a side effect, we can make the tcp_build_frag helper static.

Finally, we can pull Eric's revert.

RFC -> v1:
 - drop driver specific patch - no more needed after helper rename
 - rename skb_entail -> tcp_skb_entail (Eric)
 - preserve the tcp_build_frag helpwe, just make it static (Eric)
====================

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

1 files changed, 77 insertions, 60 deletions

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index dbcebf56798f..7e5f76092b64 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1224,6 +1224,7 @@ static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
 		if (likely(__mptcp_add_ext(skb, gfp))) {
 			skb_reserve(skb, MAX_TCP_HEADER);
 			skb->reserved_tailroom = skb->end - skb->tail;
+			INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
 			return skb;
 		}
 		__kfree_skb(skb);
@@ -1233,31 +1234,23 @@ static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
 	return NULL;
 }
 
-static bool __mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
+static struct sk_buff *__mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
 {
 	struct sk_buff *skb;
 
-	if (ssk->sk_tx_skb_cache) {
-		skb = ssk->sk_tx_skb_cache;
-		if (unlikely(!skb_ext_find(skb, SKB_EXT_MPTCP) &&
-			     !__mptcp_add_ext(skb, gfp)))
-			return false;
-		return true;
-	}
-
 	skb = __mptcp_do_alloc_tx_skb(sk, gfp);
 	if (!skb)
-		return false;
+		return NULL;
 
 	if (likely(sk_wmem_schedule(ssk, skb->truesize))) {
-		ssk->sk_tx_skb_cache = skb;
-		return true;
+		tcp_skb_entail(ssk, skb);
+		return skb;
 	}
 	kfree_skb(skb);
-	return false;
+	return NULL;
 }
 
-static bool mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, bool data_lock_held)
+static struct sk_buff *mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, bool data_lock_held)
 {
 	gfp_t gfp = data_lock_held ? GFP_ATOMIC : sk->sk_allocation;
 
@@ -1287,23 +1280,29 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 			      struct mptcp_sendmsg_info *info)
 {
 	u64 data_seq = dfrag->data_seq + info->sent;
+	int offset = dfrag->offset + info->sent;
 	struct mptcp_sock *msk = mptcp_sk(sk);
 	bool zero_window_probe = false;
 	struct mptcp_ext *mpext = NULL;
-	struct sk_buff *skb, *tail;
-	bool must_collapse = false;
-	int size_bias = 0;
-	int avail_size;
-	size_t ret = 0;
+	bool can_coalesce = false;
+	bool reuse_skb = true;
+	struct sk_buff *skb;
+	size_t copy;
+	int i;
 
 	pr_debug("msk=%p ssk=%p sending dfrag at seq=%llu len=%u already sent=%u",
 		 msk, ssk, dfrag->data_seq, dfrag->data_len, info->sent);
 
+	if (WARN_ON_ONCE(info->sent > info->limit ||
+			 info->limit > dfrag->data_len))
+		return 0;
+
 	/* compute send limit */
 	info->mss_now = tcp_send_mss(ssk, &info->size_goal, info->flags);
-	avail_size = info->size_goal;
+	copy = info->size_goal;
+
 	skb = tcp_write_queue_tail(ssk);
-	if (skb) {
+	if (skb && copy > skb->len) {
 		/* Limit the write to the size available in the
 		 * current skb, if any, so that we create at most a new skb.
 		 * Explicitly tells TCP internals to avoid collapsing on later
@@ -1316,62 +1315,80 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
 			goto alloc_skb;
 		}
 
-		must_collapse = (info->size_goal > skb->len) &&
-				(skb_shinfo(skb)->nr_frags < sysctl_max_skb_frags);
-		if (must_collapse) {
-			size_bias = skb->len;
-			avail_size = info->size_goal - skb->len;
+		i = skb_shinfo(skb)->nr_frags;
+		can_coalesce = skb_can_coalesce(skb, i, dfrag->page, offset);
+		if (!can_coalesce && i >= sysctl_max_skb_frags) {
+			tcp_mark_push(tcp_sk(ssk), skb);
+			goto alloc_skb;
 		}
-	}
 
+		copy -= skb->len;
+	} else {
 alloc_skb:
-	if (!must_collapse &&
-	    !mptcp_alloc_tx_skb(sk, ssk, info->data_lock_held))
-		return 0;
+		skb = mptcp_alloc_tx_skb(sk, ssk, info->data_lock_held);
+		if (!skb)
+			return -ENOMEM;
+
+		i = skb_shinfo(skb)->nr_frags;
+		reuse_skb = false;
+		mpext = skb_ext_find(skb, SKB_EXT_MPTCP);
+	}
 
 	/* Zero window and all data acked? Probe. */
-	avail_size = mptcp_check_allowed_size(msk, data_seq, avail_size);
-	if (avail_size == 0) {
+	copy = mptcp_check_allowed_size(msk, data_seq, copy);
+	if (copy == 0) {
 		u64 snd_una = READ_ONCE(msk->snd_una);
 
-		if (skb || snd_una != msk->snd_nxt)
+		if (snd_una != msk->snd_nxt) {
+			tcp_remove_empty_skb(ssk, tcp_write_queue_tail(ssk));
 			return 0;
+		}
+
 		zero_window_probe = true;
 		data_seq = snd_una - 1;
-		avail_size = 1;
-	}
+		copy = 1;
 
-	if (WARN_ON_ONCE(info->sent > info->limit ||
-			 info->limit > dfrag->data_len))
-		return 0;
+		/* all mptcp-level data is acked, no skbs should be present into the
+		 * ssk write queue
+		 */
+		WARN_ON_ONCE(reuse_skb);
+	}
 
-	ret = info->limit - info->sent;
-	tail = tcp_build_frag(ssk, avail_size + size_bias, info->flags,
-			      dfrag->page, dfrag->offset + info->sent, &ret);
-	if (!tail) {
-		tcp_remove_empty_skb(sk, tcp_write_queue_tail(ssk));
+	copy = min_t(size_t, copy, info->limit - info->sent);
+	if (!sk_wmem_schedule(ssk, copy)) {
+		tcp_remove_empty_skb(ssk, tcp_write_queue_tail(ssk));
 		return -ENOMEM;
 	}
 
-	/* if the tail skb is still the cached one, collapsing really happened.
-	 */
-	if (skb == tail) {
-		TCP_SKB_CB(tail)->tcp_flags &= ~TCPHDR_PSH;
-		mpext->data_len += ret;
+	if (can_coalesce) {
+		skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
+	} else {
+		get_page(dfrag->page);
+		skb_fill_page_desc(skb, i, dfrag->page, offset, copy);
+	}
+
+	skb->len += copy;
+	skb->data_len += copy;
+	skb->truesize += copy;
+	sk_wmem_queued_add(ssk, copy);
+	sk_mem_charge(ssk, copy);
+	skb->ip_summed = CHECKSUM_PARTIAL;
+	WRITE_ONCE(tcp_sk(ssk)->write_seq, tcp_sk(ssk)->write_seq + copy);
+	TCP_SKB_CB(skb)->end_seq += copy;
+	tcp_skb_pcount_set(skb, 0);
+
+	/* on skb reuse we just need to update the DSS len */
+	if (reuse_skb) {
+		TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
+		mpext->data_len += copy;
 		WARN_ON_ONCE(zero_window_probe);
 		goto out;
 	}
 
-	mpext = skb_ext_find(tail, SKB_EXT_MPTCP);
-	if (WARN_ON_ONCE(!mpext)) {
-		/* should never reach here, stream corrupted */
-		return -EINVAL;
-	}
-
 	memset(mpext, 0, sizeof(*mpext));
 	mpext->data_seq = data_seq;
 	mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
-	mpext->data_len = ret;
+	mpext->data_len = copy;
 	mpext->use_map = 1;
 	mpext->dsn64 = 1;
 
@@ -1380,18 +1397,18 @@ alloc_skb:
 		 mpext->dsn64);
 
 	if (zero_window_probe) {
-		mptcp_subflow_ctx(ssk)->rel_write_seq += ret;
+		mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
 		mpext->frozen = 1;
 		if (READ_ONCE(msk->csum_enabled))
-			mptcp_update_data_checksum(tail, ret);
+			mptcp_update_data_checksum(skb, copy);
 		tcp_push_pending_frames(ssk);
 		return 0;
 	}
 out:
 	if (READ_ONCE(msk->csum_enabled))
-		mptcp_update_data_checksum(tail, ret);
-	mptcp_subflow_ctx(ssk)->rel_write_seq += ret;
-	return ret;
+		mptcp_update_data_checksum(skb, copy);
+	mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
+	return copy;
 }
 
 #define MPTCP_SEND_BURST_SIZE		((1 << 16) - \