On 17/10/2016 22:50, Karl Denninger wrote:
I will make some effort on the sandbox machine to see if I can come up
with a way to replicate this.  I do have plenty of spare larger drives
laying around that used to be in service and were obsolesced due to
capacity -- but what I don't know if whether the system will misbehave
if the source is all spinning rust.

In other words:

1. Root filesystem is mirrored spinning rust (production is mirrored SSDs)

2. Backup is mirrored spinning rust (of approx the same size)

3. Set up auto-snapshot exactly as the production system has now (which
the sandbox is NOT since I don't care about incremental recovery on that
machine; it's a sandbox!)

4. Run a bunch of build-somethings (e.g. buildworlds, cross-build for
the Pi2s I have here, etc) to generate a LOT of filesystem entropy
across lots of snapshots.

5. Back that up.

6. Export the backup pool.

7. Re-import it and "zfs destroy -r" the backup filesystem.

That is what got me in a reboot loop after the *first* panic; I was
simply going to destroy the backup filesystem and re-run the backup, but
as soon as I issued that zfs destroy the machine panic'd and as soon as
I re-attached it after a reboot it panic'd again.  Repeat until I set

But... if I CAN replicate it that still shouldn't be happening, and the
system should *certainly* survive attempting to TRIM on a vdev that
doesn't support TRIMs, even if the removal is for a large amount of
space and/or files on the target, without blowing up.

BTW I bet it isn't that rare -- if you're taking timed snapshots on an
active filesystem (with lots of entropy) and then make the mistake of
trying to remove those snapshots (as is the case with a zfs destroy -r
or a zfs recv of an incremental copy that attempts to sync against a
source) on a pool that has been imported before the system realizes that
TRIM is unavailable on those vdevs.

Noting this:

     Yes need to find some time to have a look at it, but given how rare
     this is and with TRIM being re-implemented upstream in a totally
     different manor I'm reticent to spend any real time on it.

What's in-process in this regard, if you happen to have a reference?
Looks like it may be still in review: https://reviews.csiden.org/r/263/

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