Created attachment 837889 [details]
system log

I've had on a few systems since update to kernel 4.12.14-lp151.28.48-default 
spontaneous and sudden full btrfs filesystems. During a few seconds the
filesystem is full without a user reason. The filesystems had before e.g. 30 %
free space (>15GB). I know that i can't exclude some programs, which fill the
space quickly.
But i hadn't such effects before this kernel and the monitoring doesn't show an
growing used space during fillup, only the free space is going down.
I haven't only a few snapshots on the filesystems.
I can get the space again if i delete the oldest snapshots.
So it seems that the snapshot referenced space is suddenly increasing ?!

If this happens, some backup jobs were running (reading from the filesystem)
and  some snapper or btrfs maintenance tasks (snapper timeline, which isn't
configured; btrfs balance; btrfs scrub) were running.
It seems like a race condition, which i can't reproduce, but it is really a
nasty situation if this is happening.