mptcp: stop relying on tcp_tx_skb_cache

We want to revert the skb TX cache, but MPTCP is currently
using it unconditionally.

Rework the MPTCP tx code, so that tcp_tx_skb_cache is not
needed anymore: do the whole coalescing check, skb allocation
skb initialization/update inside mptcp_sendmsg_frag(), quite
alike the current TCP code.

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index dbcebf56798fa80a87eb8abd89b35fa13ed85d60..7e5f76092b649677d2a225d26f3fbe116fae2993 100644 (file)
--- 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) - \