Patchwork [185/222] tcp: fix MSG_SENDPAGE_NOTLAST logic

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Submitter Herton Ronaldo Krzesinski
Date Jan. 16, 2013, 3:56 p.m.
Message ID <1358351822-7675-186-git-send-email-herton.krzesinski@canonical.com>
Download mbox | patch
Permalink /patch/212759/
State New
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Herton Ronaldo Krzesinski - Jan. 16, 2013, 3:56 p.m.
3.5.7.3 -stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@google.com>

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: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
---
 fs/splice.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
Ben Hutchings - Feb. 1, 2013, 5:40 p.m.
On Wed, 2013-01-16 at 13:56 -0200, Herton Ronaldo Krzesinski wrote:
> 3.5.7.3 -stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Eric Dumazet <edumazet@google.com>
> 
> 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.
[...]

David, I think this is needed for 3.0 and 3.2 as well since
35f9c09fe9c72e was backported to them.  You previously included it in
updates for 3.4 and 3.7.

Ben.
David Miller - Feb. 12, 2013, 7:36 a.m.
From: Ben Hutchings <ben@decadent.org.uk>
Date: Fri, 01 Feb 2013 18:40:57 +0100

> On Wed, 2013-01-16 at 13:56 -0200, Herton Ronaldo Krzesinski wrote:
>> 3.5.7.3 -stable review patch.  If anyone has any objections, please let me know.
>> 
>> ------------------
>> 
>> From: Eric Dumazet <edumazet@google.com>
>> 
>> 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.
> [...]
> 
> David, I think this is needed for 3.0 and 3.2 as well since
> 35f9c09fe9c72e was backported to them.  You previously included it in
> updates for 3.4 and 3.7.

Ok, queued up, thanks.

Patch

diff --git a/fs/splice.c b/fs/splice.c
index 7bf08fa..6cb3acb 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);
 }