Patchwork tcp: fix MSG_SENDPAGE_NOTLAST logic

login
register
mail settings
Submitter Eric Dumazet
Date Jan. 7, 2013, 4:21 a.m.
Message ID <1357532509.6919.1715.camel@edumazet-glaptop>
Download mbox | patch
Permalink /patch/209850/
State Accepted
Delegated to: David Miller
Headers show

Comments

Eric Dumazet - Jan. 7, 2013, 4:21 a.m.
From: Eric Dumazet <edumazet@google.com>

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>
---
 fs/splice.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)



--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
David Miller - Jan. 7, 2013, 4:59 a.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Sun, 06 Jan 2013 20:21:49 -0800

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

Applied and queued up for -stable, thanks everyone.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Patch

diff --git a/fs/splice.c b/fs/splice.c
index 8890604..6909d89 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);
 }