tcp: fix MSG_SENDPAGE_NOTLAST logic

commit 35f9c09fe9c72e (tcp: tcp_sendpages() should call tcp_push() once)
added an internal flag : MSG_SENDPAGE_NOTLAST meant to be set on all
frags but the last one for a splice() call.

The condition used to set the flag in pipe_to_sendpage() relied on
splice() user passing the exact number of bytes present in the pipe,
or a smaller one.

But some programs pass an arbitrary high value, and the test fails.

The effect of this bug is a lack of tcp_push() at the end of a
splice(pipe -> socket) call, and possibly very slow or erratic TCP
sessions.

We should both test sd->total_len and fact that another fragment
is in the pipe (pipe->nrbufs > 1)

Many thanks to Willy for providing very clear bug report, bisection
and test programs.

Reported-by: Willy Tarreau <w@1wt.eu>
Bisected-by: Willy Tarreau <w@1wt.eu>
Tested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 1 deletions

diff --git a/fs/splice.c b/fs/splice.c
index 8890604e3fcd..6909d89d0da5 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -696,8 +696,10 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
                 return -EINVAL;
 
         more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
-        if (sd->len < sd->total_len)
+
+        if (sd->len < sd->total_len && pipe->nrbufs > 1)
                 more |= MSG_SENDPAGE_NOTLAST;
+
         return file->f_op->sendpage(file, buf->page, buf->offset,
                                     sd->len, &pos, more);
 }