xfssyncd keeps disks awake

[Andrew Lutomirski]

I have an XFS filesystem on RAID5 (actually XFS on LVM on dm-crypt on
RAID5, but I doubt that matters).  Every few seconds, xfssyncd writes
something, so my disks never spin down.  As far as I can tell, there
is nothing at all accessing that partition.  (I can even unmount it.)

block_dump shows things like this:

xfssyncd/dm-4(957): WRITE block 1181327312 on dm-4 (2 sectors)
md1_raid5(842): WRITE block 0 on sda2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdb2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdc2 (2 sectors)
md1_raid5(842): WRITE block 0 on sda2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdb2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdc2 (2 sectors)
xfssyncd/dm-4(957): WRITE block 1181327314 on dm-4 (2 sectors)
md1_raid5(842): WRITE block 0 on sda2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdb2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdc2 (2 sectors)
md1_raid5(842): WRITE block 0 on sda2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdb2 (2 sectors)
md1_raid5(842): WRITE block 0 on sdc2 (2 sectors)

I have this problem on Fedora's 2.6.35 and on kernel.org's 2.6.37.  Any ideas?

--Andy