Hi,

Using Kernel 4.7.1 ( openSUSE Tumbleweed x86_64 ), btrfsprogs 4.7 I
always get a hard lockup when trying to mount my btrfs root partition.

This may be due to some previous errors which only manifested
themselves now, as it's been converted from an ext4 partition.

Using mount -o ro works. Using mount -o recovery or mounting without
arguments does not. I've managed to capture one of the error messages,
but via screenshot only. I've transcribed some of it below, more at

  http://i.imgur.com/OSIddHE.jpg

BTRFS info (device sda1): disk space caching is enabled
BTRFS info (device sda1): detected SSD devices, enabling SSD mode
BTRFS info (device sda1): checking UUID tree
BTRFS info (device sda1): continuing balance
BTRFS info (device sda1): relocating block group 1047892328448 flags 1
BTRFS info (device sda1): found 805 extents
(...)
kernel BUG at ../fs/btrfs/extent-tree.c:1872
invalid opcode: 0000 [#1] PREEMPT SMP
(...)
Workqueue: btrfs-extent-refs btrfs_extent_refs_helper [btrfs]
(...)
Call Trace:
 [...] remove_extent_backref
 [...] __btrfs_free_extent_isra
 [...] __btrfs_run_delayed
 [...] delayed_ref_async_start
 [...] btrfs_scrubparity_helper
 [...] process_one_work
 [...] worked_thread
 [...] kthread
 [...] ret_from_fork
DWARF2 unwinder stuck at ret_from_fork

For reference, I've attached the output of

- btrfsck /dev/sda1
- btrfsck --repair /dev/sda1
- btrfsck --repair /dev/sda1 (2nd execution)

I've included two executions in repair mode to show that nothing of
interest changes between the two.

My way out is simply transferring the data out ( mount -o ro works )
and creating a new partition, but it would be interesting to fix it,
and if there's any information I can offer to help prepare a bug fix
please let me know.

Thanks,

Robert

-- 
http://robert.muntea.nu/