kern/51275: syncing a full lfs wedges

[dholland%NetBSD.org@localhost]

>Number:         51275
>Category:       kern
>Synopsis:       syncing a full lfs wedges
>Confidential:   no
>Severity:       critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Jun 26 07:50:00 +0000 2016
>Originator:     David A. Holland
>Release:        NetBSD 7.99.31 (20160620)
>Organization:
>Environment:
System: NetBSD amnesiac 7.99.31 NetBSD 7.99.31 (GENERIC) #14: Sun Jun 26 03:11:19 EDT 2016  dholland@valkyrie:/y/trees/netbsd/lfs2/sys/arch/amd64/compile/obj.amd64/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:


	% dd if=/dev/zero of=image bs=102400 count=1000
	% newfs_lfs ./image
	% qemu-system-x86_64 -nographic -m 64 -hda rootdisk -hdb image
	(rootdisk is from anita install)
	[...]
	# mount -t lfs /dev/wd1b /mnt
	# cd /mnt
	# dd if=/dev/zero of=blef bs=64k
	dd: blef: No space left on device
	1228+0 records in
	1227+0 records out
	80412672 bytes transferred in 2.261 secs (35565091 bytes/sec)
	# sync
	# <hangs>

If you don't sync, things seem to be fine (at least for a while); if
the volume isn't full, syncing isn't lethal.

If you do sync you get a prompt back and there's 1-2 seconds before it
wedges.

>How-To-Repeat:

>Fix: