linux-kernel - [ 090/123] tcp: fix MSG_SENDPAGE

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Date:	Wed,  9 Jan 2013 12:35:29 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Willy Tarreau <w@....eu>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 090/123] tcp: fix MSG_SENDPAGE_NOTLAST logic

3.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit ae62ca7b03217be5e74759dc6d7698c95df498b3 ]

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@....eu>
Bisected-by: Willy Tarreau <w@....eu>
Tested-by: Willy Tarreau <w@....eu>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/splice.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/fs/splice.c
+++ b/fs/splice.c
@@ -696,8 +696,10 @@ static int pipe_to_sendpage(struct 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);
 }

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