svn commit: r343047 - head/sys/netinet

[Stephen Hurd]

Author: shurd
Date: Tue Jan 15 17:40:19 2019
New Revision: 343047
URL: https://svnweb.freebsd.org/changeset/base/343047

Log:
  Fix window update issue when scaling disabled
  
  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

Modified:
  head/sys/netinet/tcp_output.c

Modified: head/sys/netinet/tcp_output.c
==============================================================================
--- head/sys/netinet/tcp_output.c	Tue Jan 15 16:12:47 2019	(r343046)
+++ head/sys/netinet/tcp_output.c	Tue Jan 15 17:40:19 2019	(r343047)
@@ -656,7 +656,8 @@ after_sack_rexmit:
 		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;