Panic in ZFS during zfs recv (while snapshots being destroyed)

[Karl Denninger]

I have an automated script that runs zfs send/recv copies to bring a
backup data set into congruence with the running copies nightly.  The
source has automated snapshots running on a fairly frequent basis
through zfs-auto-snapshot.

Recently I have started having a panic show up about once a week during
the backup run, but it's inconsistent.  It is in the same place, but I
cannot force it to repeat.

The trap itself is a page fault in kernel mode in the zfs code at
zfs_unmount_snap(); here's the traceback from the kvm (sorry for the
image link but I don't have a better option right now.)

I'll try to get a dump, this is a production machine with encrypted swap
so it's not normally turned on.

Note that the pool that appears to be involved (the backup pool) has
passed a scrub and thus I would assume the on-disk structure is ok.....
but that might be an unfair assumption.  It is always occurring in the
same dataset although there are a half-dozen that are sync'd -- if this
one (the first one) successfully completes during the run then all the
rest will as well (that is, whenever I restart the process it has always
failed here.)  The source pool is also clean and passes a scrub.

traceback is at http://www.denninger.net/kvmimage.png; apologies for the
image traceback but this is coming from a remote KVM.

I first saw this on 10.1-STABLE and it is still happening on FreeBSD
10.2-PRERELEASE #9 r285890M, which I updated to in an attempt to see if
the problem was something that had been addressed.


-- 
Karl Denninger
karl at denninger.net <mailto:karl at denninger.net>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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