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

[Josef Bacik <jbacik@fb.com>]

On 09/15/2015 10:47 AM, Stéphane Lesimple wrote:
>> I've been experiencing repetitive "kernel BUG" occurences in the past
>> few days trying to balance a raid5 filesystem after adding a new drive.
>> It occurs on both 4.2.0 and 4.1.7, using 4.2 userspace tools.
>
> I've ran a scrub on this filesystem after the crash happened twice, and
> if found no errors.
>
> The BUG_ON() condition that my filesystem triggers is the following :
>
> BUG_ON(owner < BTRFS_FIRST_FREE_OBJECTID);
> // in insert_inline_extent_backref() of extent-tree.c.
>
> I've compiled a fresh 4.3.0-rc1 with a couple added printk's just before
> the BUG_ON(), to dump the parameters passed to
> insert_inline_extent_backref() when the problem occurs.
> Here is an excerpt of the resulting dmesg :
>
> {btrfs} in insert_inline_extent_backref, got owner <
> BTRFS_FIRST_FREE_OBJECTID
> {btrfs} with bytenr=4557830635520 num_bytes=16384 parent=4558111506432
> root_objectid=3339 owner=1 offset=0 refs_to_add=1
> BTRFS_FIRST_FREE_OBJECTID=256
> ------------[ cut here ]------------
> kernel BUG at fs/btrfs/extent-tree.c:1837!
>
> I'll retry with the exact same kernel once I get the machine back up,
> and see if the the bug happens again at the same filesystem spot or a
> different one.
> The variable amount of time after a balance start elapsed before I get
> the bug suggests that this would be a different one.
>

Does btrfsck complain at all?  Thanks,

Josef