Re: kernel BUG at linux-4.2.0/fs/btrfs/extent-tree.c:1833 on rebalance

["Stéphane Lesimple" <stephane_btrfs@lesimple.fr>]

Le 2015-09-16 15:04, Stéphane Lesimple a écrit :
> I also disabled quota because it has almost for sure nothing
> to do with the bug

As it turns out, it seems that this assertion was completely wrong.

I've got balance running for more than 16 hours now, without a crash. 
This is almost 50% of the work done without any issue. Before, a crash 
would happen within minutes, sometimes 1 hour, but not much more. The 
problem is, I didn't change anything to the filesystem, well, appart 
from the benign quota disable. So Qu's question about the qgroups errors 
in fsck made me wonder : if I activate quota again, it'll still continue 
to balance flawlessly, right ?

Well, it doesn't. I just ran btrfs quota enable on my filesystem, it 
completed successfully after some minutes (rescan -s said that no rescan 
was pending). Then less than 5 minutes later, the kernel crashed, at the 
same BUG_ON() than usually :

[60156.062082] BTRFS info (device dm-3): relocating block group 
972839452672 flags 129
[60185.203626] BTRFS info (device dm-3): found 1463 extents
[60414.452890] {btrfs} in insert_inline_extent_backref, got owner < 
BTRFS_FIRST_FREE_OBJECTID
[60414.452894] {btrfs} with bytenr=5197436141568 num_bytes=16384 
parent=5336636473344 root_objectid=3358 owner=1 offset=0 refs_to_add=1 
BTRFS_FIRST_FREE_OBJECTID=256
[60414.452924] ------------[ cut here ]------------
[60414.452928] kernel BUG at fs/btrfs/extent-tree.c:1837!

owner is=1 again at this point in the code (this is still kernel 
4.3.0-rc1 with my added printks).

So I'll disable quota, again, and resume the balance. If I'm right, it 
should proceed without issue for 18 more hours !

Qu, my filesystem is at your disposal :)

-- 
Stéphane.