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

[Karl Denninger]

Update:

This /appears /to be related to attempting to send or receive a /cloned
/snapshot.

I use /beadm /to manage boot environments and the crashes have all come
while send/recv-ing the root pool, which is the one where these clones
get created.  It is /not /consistent within a given snapshot when it
crashes and a second attempt (which does a "recovery" send/receive)
succeeds every time -- I've yet to have it panic twice sequentially.

I surmise that the problem comes about when a file in the cloned
snapshot is modified, but this is a guess at this point.

I'm going to try to force replication of the problem on my test system.

On 7/31/2015 04:47, Karl Denninger wrote:
> 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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