Re: [PATCH] tcp: fix MSG_SENDPAGE_NOTLAST logic

David Miller
2013-01-07T04:59:39Z

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.