kern/49235: can't send fax anymore with 6.1.4 kernel

[is%beverly.kleinbus.org@localhost]

>Number:         49235
>Category:       kern
>Synopsis:       can't send fax anymore with a 6.1.4 kernel
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 24 09:00:00 +0000 2014
>Originator:     Ignatios Souvatzis
>Release:        NetBSD 6.1.4_PATCH
>Organization:
>Environment:
System: NetBSD marie 6.1.4_PATCH NetBSD 6.1.4_PATCH (MARIE) #4: Sat Aug 23 20:25:06 CEST 2014 is@henrietta:/var/itch/sources/6.1/obj.shark/sys/arch/shark/compile/MARIE shark
Architecture: arm
Machine: shark

com0 at ofisa0 (serial@i3f8): ns16550a, working fifo
com1 at ofisa0 (ir@i2f8): ns16550a, working fifo

>Description:
	When sending a fax, actual fax transmission aborts a few
	seconds (according to log) after starting the first page;
	the receiving fax machine prints the first ca. three (dot) lines.

	The sendfax process sees this error at this point:

	09/24 08:30:53 y00   input: got [0d][0a]+FHS:43[0d][0a]

	FHS:43 is "DTE to DCE data underflow  "

	which points to something broken with flow control.
	Debug output sees us sending more data, 64bytes at a time,
	continuing until the page has been sent.

	the serial used is com0 - see above.

>How-To-Repeat:
	faxspool ... ; faxrunq
>Fix:
	workaround: rebooting to the 5.1.3_PATCH kernel
	(obviously only with 5.1.3 userland)

>Unformatted:
 
 On this kernel,
 
 	checked with 5.1.3_PATCH userland / mgetty-1.1.37nb9
 	checked with 6.1_PATCH   userland / mgetty-1.1.37nb10
 
 resulting in the same error.