[TCP]: Fix sk_forward_alloc underflow in tcp_sendmsg

I've finally found a potential cause of the sk_forward_alloc underflows
that people have been reporting sporadically.

When tcp_sendmsg tacks on extra bits to an existing TCP_PAGE we don't
check sk_forward_alloc even though a large amount of time may have
elapsed since we allocated the page.  In the mean time someone could've
come along and liberated packets and reclaimed sk_forward_alloc memory.

This patch makes tcp_sendmsg check sk_forward_alloc every time as we
do in do_tcp_sendpages.
 
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 3 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index e51e626e9af1..cf628261da52 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1232,9 +1232,8 @@ static inline struct page *sk_stream_alloc_page(struct sock *sk)
 {
         struct page *page = NULL;
 
-        if (sk_stream_wmem_schedule(sk, PAGE_SIZE))
-                page = alloc_pages(sk->sk_allocation, 0);
-        else {
+        page = alloc_pages(sk->sk_allocation, 0);
+        if (!page) {
                 sk->sk_prot->enter_memory_pressure();
                 sk_stream_moderate_sndbuf(sk);
         }