tcp: fix MSG_SENDPAGE_NOTLAST logic

commit ae62ca7b03217be5e74759dc6d7698c95df498b3 upstream.

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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/fs/splice.c b/fs/splice.c
index 3bec7c63be642f2a0dd3b99f8ea5e9e762370263..1c991d6a64b4604d34a63ac008fea6ae0eeb30c2 100644 (file)
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -640,8 +640,10 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
        ret = buf->ops->confirm(pipe, buf);
        if (!ret) {
                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;
+
                if (file->f_op && file->f_op->sendpage)
                        ret = file->f_op->sendpage(file, buf->page, buf->offset,
                                                   sd->len, &pos, more);