Re: [PATCH] Btrfs: fix deadlock with nested trans handles

[Josef Bacik <jbacik@fb.com>]

On 03/14/2014 06:40 PM, Rich Freeman wrote:
> On Wed, Mar 12, 2014 at 12:34 PM, Rich Freeman
> <r-btrfs@thefreemanclan.net> wrote:
>> On Wed, Mar 12, 2014 at 11:24 AM, Josef Bacik <jbacik@fb.com> wrote:
>>> On 03/12/2014 08:56 AM, Rich Freeman wrote:
>>>>
>>>>   After a number of reboots the system became stable, presumably
>>>> whatever race condition btrfs was hitting followed a favorable
>>>> path.
>>>>
>>>> I do have a 2GB btrfs-image pre-dating my application of this
>>>> patch that was causing the issue last week.
>>>>
>>>
>>> Uhm wow that's pretty epic.  I will talk to chris and figure out how
>>> we want to deal with that and send you a patch shortly.  Thanks,
>>
>> A tiny bit more background.
>
> And some more background.  I had more reboots over the next two days
> at the same time each day, just after my crontab successfully
> completed.  One of the last thing it does is runs the snapper cleanups
> which delete a bunch of snapshots.  During a reboot I checked and
> there were a bunch of deleted snapshots, which disappeared over the
> next 30-60 seconds before the panic, and then they would re-appear on
> the next reboot.
>
> I disabled the snapper cron job and this morning had no issues at all.
>   One day isn't much to establish a trend, but I suspect that this is
> the cause.  Obviously getting rid of snapshots would be desirable at
> some point, but I can wait for a patch.  Snapper would be deleting
> about 48 snapshots at the same time, since I create them hourly and
> the cleanup occurs daily on two different subvolumes on the same
> filesystem.

Ok that's helpful, I'm no longer positive I know what's causing this, 
I'll try to reproduce once I've nailed down these backref problems and 
balance corruption.  Thanks,

Josef