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Fix window update issue when scaling disabled

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When the TCP window scale option is not used, and the window
opens up enough in one soreceive, a window update will not be sent.

For example, if recwin == 65535, so->so_rcv.sb_hiwat >= 262144, and
so->so_rcv.sb_hiwat <= 524272, the window update will never be sent.
This is because recwin and adv are clamped to TCP_MAXWIN << tp->rcv_scale,
and so will never be >= so->so_rcv.sb_hiwat / 4
or <= so->so_rcv.sb_hiwat / 8.

This patch ensures a window update is sent if the window opens by
TCP_MAXWIN << tp->rcv_scale, which should only happen when the window
size goes from zero to the max expressible.

This issue looks like it was introduced in r306769 when recwin was clamped
to TCP_MAXWIN << tp->rcv_scale.

MFC after:	1 week
Sponsored by:	Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D18821
This commit is contained in:
Stephen Hurd 2019-01-15 17:40:19 +00:00
parent d366f891b1
commit 500759395a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=343047
1 changed files with 2 additions and 1 deletions
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3
sys/netinet/tcp_output.c
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@ -656,7 +656,8 @@ tcp_output(struct tcpcb *tp)
if (adv >= (int32_t)(2 * tp->t_maxseg) &&
(adv >= (int32_t)(so->so_rcv.sb_hiwat / 4) ||
recwin <= (so->so_rcv.sb_hiwat / 8) ||
so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg))
so->so_rcv.sb_hiwat <= 8 * tp->t_maxseg ||
adv >= TCP_MAXWIN << tp->rcv_scale))
goto send;
if (2 * adv >= (int32_t)so->so_rcv.sb_hiwat)
goto send;