With this new kernel, I notice two messages I do not have with
2.6.19-rc6-mm2 :

Dec 15 20:00:47 brouette kernel: Filesystem "sdb9": Disabling barriers,trial barrier write failed
Dec 15 20:00:47 brouette kernel: Filesystem "sda5": Disabling barriers,trial barrier write failed

Nothing changed in the config between the two, and going back to
2.6.19-rc6-mm2 do not give the messages.

Also, I got panics when unmounting reiser4 filesystems with
2.6.20-rc1-mm1 but I guess this is related to your waring about reiser4
being broken in 2.6.19-mm1 (even if it is not listed in notes for
2.6.20-rc1-mm1)... I attach dmesg and config, but the reiser4 panics did
not get logged and I am not able to reboot on 2.6.20-rc1-mm1 right now.
For the moment, I mainly wanted to report the xfs messages which seems
a bit suspect.

-- 
Damien Wyart