On 06/07/2019 05.51, Qu Wenruo wrote:
>> The problem also manifests when attempting to rebalance the metadata.
> 
> Have you tried to balance just one or two metadata block groups?
> E.g using -mdevid or -mvrange?

If I use -mdevid with the device ID of the device I'm trying to remove 
(2), I see the crash.

If I use -mvrange with a range covering one byte past a problematic 
virtual address, I see the crash.

Not sure if you had anything else / specific in mind. Here is a log of 
my experiments so far:

https://dump.thecybershadow.net/da241fb4b6e743b01a7e9f8734f70d6e/scratch.txt

> And did the problem always happen at the same block group?

Upon reviewing my logs, it looks like for "device remove" it always 
tries to move block group 1998263943168 first, upon which it crashes.

For "balance", it seems to vary - looks like there is at least one other 
problematic block group at 48009543942144.

Happy to do more experiments or test kernel patches. I have a VM set up 
with a COW view of the devices, so I can do destructive tests too.

-- 
Best regards,
  Vladimir