On 2019-09-30 9:53 p.m., Qu Wenruo wrote:

> 
> It's indeed a symptom of btrfs kernel module bug. But at least looks
> repairable.
> 

As advertised, btrfs --check repair restored the FS to full function.

A follow-up scrub even found and corrected some corrupt data on one of
the disks, that went  completely unreported by the disk itself.  So,
despite this hiccup, BTRFS did it's job admirably.


Whenever I do any further btrfs check after cleanly unmounting the
filesystem, I get this error:

cache and super generation don't match, space cache will be invalidated

Even mounting with clear_cache,nospace_cache , (then mounting again with
space_cache=v2) does not remove this warning.  But it doesn't seem to be
causing any problems.. There are no warnings about the space cache in
the dmesg log when the filesystem is mounted.