kernel BUG at fs/btrfs/free-space-cache.c:1542!

[scorpp]

Looks very similar to https://bugzilla.redhat.com/show_bug.cgi?id=923542
Here are details of my case:

i have couple of btrfs partitions one of which stops working for second time now with same symptoms (see dmesg). Others are working fine at the same time.
After the first failure i was able to get partition back to life by addtion nospace_cache option to fstab and rebooting. After that everything worked fine for a few weeks up until today.
Partition was always mounted like this

/dev/mapper/vg0-var /var btrfs defaults,compress=lzo 0 0

I created partition image just like you said in redhat bugzilla comment with git version of btrfs-image tool

$ uname -a
Linux archbang 3.8.7-1-pae #1 SMP PREEMPT Mon Apr 15 18:39:53 EDT 2013 i686 GNU/Linux

You could also see details of my first failure here https://bbs.archlinux.org/viewtopic.php?pid=1256798#p1256798