I've managed to corrupt my btrfs and btrfsck crashes in repair mode:

root@beast:/data/backup# btrfsck --mode=lowmem --clear-space-cache v2 /dev/md0
parent transid verify failed on 5840011722752 wanted 170755 found 170832
parent transid verify failed on 5840011722752 wanted 170755 found 170832
parent transid verify failed on 5840011722752 wanted 170755 found 170832
parent transid verify failed on 5840011722752 wanted 170755 found 170832
Ignoring transid failure
leaf parent key incorrect 5840011722752
Clear free space cache v2
parent transid verify failed on 5367057465344 wanted 170755 found 170828
parent transid verify failed on 5367057465344 wanted 170755 found 170828
parent transid verify failed on 5367057465344 wanted 170755 found 170828
parent transid verify failed on 5367057465344 wanted 170755 found 170828
Ignoring transid failure
leaf parent key incorrect 72105984
btrfs unable to find ref byte nr 4628577484800 parent 0 root 10  owner 0 offset 1
parent transid verify failed on 5366993256448 wanted 170755 found 170827
parent transid verify failed on 5366993256448 wanted 170755 found 170827
parent transid verify failed on 5366993256448 wanted 170755 found 170827
parent transid verify failed on 5366993256448 wanted 170755 found 170827
Ignoring transid failure
leaf parent key incorrect 41287680
ERROR: failed to clear free space cache v2: -1
transaction.h:41: btrfs_start_transaction: BUG_ON `root->commit_root` triggered, value 34947872
btrfs check[0x411674]
btrfs check(close_ctree_fs_info+0x125)[0x41368c]
btrfs check(cmd_check+0x36d8)[0x45e8e8]
btrfs check(main+0x15d)[0x40ac5c]
/lib/libc.so.6(__libc_start_main+0xf0)[0x7fb2af7a70d0]
btrfs check[0x40a729]
Aborted

Btrfsck is the latest from git:

root@beast:/build/pkg/btrfs-progs# git describe
v4.11
root@beast:/build/pkg/btrfs-progs# git log --oneline -1
981f2d8 Btrfs progs v4.11

Kernel is mainline from a few days ago, with a single networking patch on top:

root@beast:/build/pkg/btrfs-progs# uname -a
Linux beast 4.12.0-rc4 #114 SMP Fri Jun 9 16:18:57 CEST 2017 x86_64 GNU/Linux

root@beast:/build/pkg/linux-torvalds# git log --oneline -2
9e49b2b bonding: sane default value for MAX_BONDS
eb4125d Merge tag 'for-linus-4.12b-rc5-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip