releases/3.4.25/tcp-fix-msg_sendpage_notlast-logic.patch

   1 From 8b19905f4cf882dc5fbc403aa3077b01e33c5b4d Mon Sep 17 00:00:00 2001
   2 From: Eric Dumazet <edumazet@google.com>
   3 Date: Sun, 6 Jan 2013 18:21:49 +0000
   4 Subject: tcp: fix MSG_SENDPAGE_NOTLAST logic
   5
   6
   7 From: Eric Dumazet <edumazet@google.com>
   8
   9 [ Upstream commit ae62ca7b03217be5e74759dc6d7698c95df498b3 ]
  10
  11 commit 35f9c09fe9c72e (tcp: tcp_sendpages() should call tcp_push() once)
  12 added an internal flag : MSG_SENDPAGE_NOTLAST meant to be set on all
  13 frags but the last one for a splice() call.
  14
  15 The condition used to set the flag in pipe_to_sendpage() relied on
  16 splice() user passing the exact number of bytes present in the pipe,
  17 or a smaller one.
  18
  19 But some programs pass an arbitrary high value, and the test fails.
  20
  21 The effect of this bug is a lack of tcp_push() at the end of a
  22 splice(pipe -> socket) call, and possibly very slow or erratic TCP
  23 sessions.
  24
  25 We should both test sd->total_len and fact that another fragment
  26 is in the pipe (pipe->nrbufs > 1)
  27
  28 Many thanks to Willy for providing very clear bug report, bisection
  29 and test programs.
  30
  31 Reported-by: Willy Tarreau <w@1wt.eu>
  32 Bisected-by: Willy Tarreau <w@1wt.eu>
  33 Tested-by: Willy Tarreau <w@1wt.eu>
  34 Signed-off-by: Eric Dumazet <edumazet@google.com>
  35 Signed-off-by: David S. Miller <davem@davemloft.net>
  36 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  37 ---
  38  fs/splice.c |    4 +++-
  39  1 file changed, 3 insertions(+), 1 deletion(-)
  40
  41 --- a/fs/splice.c
  42 +++ b/fs/splice.c
  43 @@ -696,8 +696,10 @@ static int pipe_to_sendpage(struct pipe_
  44                 return -EINVAL;
  45
  46         more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
  47 -       if (sd->len < sd->total_len)
  48 +
  49 +       if (sd->len < sd->total_len && pipe->nrbufs > 1)
  50                 more |= MSG_SENDPAGE_NOTLAST;
  51 +
  52         return file->f_op->sendpage(file, buf->page, buf->offset,
  53                                     sd->len, &pos, more);
  54  }