tcp: tcp_sendpages() should call tcp_push() once

commit 2f533844242 (tcp: allow splice() to build full TSO packets) added
a regression for splice() calls using SPLICE_F_MORE.

We need to call tcp_flush() at the end of the last page processed in
tcp_sendpages(), or else transmits can be deferred and future sends
stall.

Add a new internal flag, MSG_SENDPAGE_NOTLAST, acting like MSG_MORE, but
with different semantic.

For all sendpage() providers, its a transparent change. Only
sock_sendpage() and tcp_sendpages() can differentiate the two different
flags provided by pipe_to_sendpage()

Reported-by: Tom Herbert <therbert@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: H.K. Jerry Chu <hkchu@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Mahesh Bandewar <maheshb@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail>com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 4 insertions, 4 deletions

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 2ff6f45a76f4..5d54ed30e821 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -860,7 +860,7 @@ wait_for_memory:
         }
 
 out:
-        if (copied && !(flags & MSG_MORE))
+        if (copied && !(flags & MSG_SENDPAGE_NOTLAST))
                 tcp_push(sk, flags, mss_now, tp->nonagle);
         return copied;
 
diff --git a/net/socket.c b/net/socket.c
index 484cc6953fc6..851edcd6b098 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -811,9 +811,9 @@ static ssize_t sock_sendpage(struct file *file, struct page *page,
 
         sock = file->private_data;
 
-        flags = !(file->f_flags & O_NONBLOCK) ? 0 : MSG_DONTWAIT;
-        if (more)
-                flags |= MSG_MORE;
+        flags = (file->f_flags & O_NONBLOCK) ? MSG_DONTWAIT : 0;
+        /* more is a combination of MSG_MORE and MSG_SENDPAGE_NOTLAST */
+        flags |= more;
 
         return kernel_sendpage(sock, page, offset, size, flags);
 }