btrfs crash 4

upgraded to 3.7rc1, worked fine
using 3.7rc1, built and installed 3.7rc2, would not boot, saying "bad superblock"


linux-it84:/mnt # btrfs fi show
Label: none  uuid: 53b579ef-9da6-4985-9a1f-11bba5cf1993
        Total devices 4 FS bytes used 190.68GiB
        devid    1 size 80.00GiB used 56.02GiB path /dev/sda3
        devid    2 size 80.00GiB used 57.00GiB path /dev/sdb3
        devid    4 size 80.00GiB used 56.01GiB path /dev/sdc3
        devid    3 size 80.00GiB used 57.01GiB path /dev/sdd3

Btrfs v0.19+20120406
linux-it84:/mnt # mount /dev/sda3 btrfs/
mount: wrong fs type, bad option, bad superblock on /dev/sda3,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so

linux-it84:/mnt # dmesg | tail
[   37.523048] nf_conntrack: automatic helper assignment is deprecated and it will be removed soon. Use the iptables CT target to attach helpers instead.
[   39.417402] NET: Registered protocol family 17
[   48.396802] EXT4-fs (dm-3): re-mounted. Opts: acl,user_xattr,commit=0
[   48.478588] EXT4-fs (md127): re-mounted. Opts: commit=0
[   48.480748] EXT4-fs (dm-1): re-mounted. Opts: commit=0
[  181.843322] Btrfs loaded
[  181.845005] device fsid 53b579ef-9da6-4985-9a1f-11bba5cf1993 devid 1 transid 49910 /dev/sda3
[  181.845722] btrfs: disk space caching is enabled
[  181.846220] btrfs: failed to read the system array on sda3
[  181.846587] btrfs: open_ctree failed

linux-it84:/home/peter/projects/btrfs-progs # ./btrfsck /dev/sda3
checking extents
checking fs roots
root 812 inode 2764202 errors 100
root 902 inode 4891484 errors 2500
found 204733300883 bytes used err is 1
total csum bytes: 193396164
total tree bytes: 6335557632
total fs tree bytes: 5609336832
btree space waste bytes: 1670043334
file data blocks allocated: 5452471107584
 referenced 632679079936
Btrfs v0.20-rc1-37-g91d9eec