tcp: fix zerocopy and notsent_lowat issues

My recent patch had at least three problems :

1) TX zerocopy wants notification when skb is acknowledged,
   thus we need to call skb_zcopy_clear() if the skb is
   cached into sk->sk_tx_skb_cache

2) Some applications might expect precise EPOLLOUT
   notifications, so we need to update sk->sk_wmem_queued
   and call sk_mem_uncharge() from sk_wmem_free_skb()
   in all cases. The SOCK_QUEUE_SHRUNK flag must also be set.

3) Reuse of saved skb should have used skb_cloned() instead
  of simply checking if the fast clone has been freed.

Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 10 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 29b94edf05f9..82bd707c0347 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -865,14 +865,9 @@ struct sk_buff *sk_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
 {
         struct sk_buff *skb;
 
-        skb = sk->sk_tx_skb_cache;
-        if (skb && !size) {
-                const struct sk_buff_fclones *fclones;
-
-                fclones = container_of(skb, struct sk_buff_fclones, skb1);
-                if (refcount_read(&fclones->fclone_ref) == 1) {
-                        sk->sk_wmem_queued -= skb->truesize;
-                        sk_mem_uncharge(sk, skb->truesize);
+        if (likely(!size)) {
+                skb = sk->sk_tx_skb_cache;
+                if (skb && !skb_cloned(skb)) {
                         skb->truesize -= skb->data_len;
                         sk->sk_tx_skb_cache = NULL;
                         pskb_trim(skb, 0);
@@ -2543,8 +2538,6 @@ void tcp_write_queue_purge(struct sock *sk)
         tcp_rtx_queue_purge(sk);
         skb = sk->sk_tx_skb_cache;
         if (skb) {
-                sk->sk_wmem_queued -= skb->truesize;
-                sk_mem_uncharge(sk, skb->truesize);
                 __kfree_skb(skb);
                 sk->sk_tx_skb_cache = NULL;
         }