ZFS deadlock

[Peter Maloney]

I've had the same thing happen. It only happens with Linux clients. My
workaround is to mount an empty directory on top of .zfs. I submitted a
PR about it also. And I can't reproduce it on other machines, including
the replicated backup server with all the same snapshots. It only
happens on the one production machine, possibly because it has more nfs
clients active than what I created for my tests.

Here's my forum thread:
http://forums.freebsd.org/showthread.php?t=29648

Here's my PR:
http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/168947


On 07/21/2012 01:50 PM, Rafi Rubin wrote:
> I have a small server with a mirrored pair of hard drives that handles
> generally light loads for a number of linux machines over nfs v3.
>
> I've been seeing some deadlocks (and possibly worse) lately.  I've
> narrowed
> down the freezing to a simple test run simultaneously on a number of the
> client machines:
>
> mount host:/food/bar
> ls bar/.zfs/snapshot
>
> When I do that, all the client machines hang on any access to the
> server.  On
> the server, only the volume "bar" hangs, the rest are fine.
>
> This occurs even when there is no other load on the server.  Also, after
> rebooting the server, the client machines eventually complete the ls and
> behave normally.
>
>
> I think this doesn't happen if the directory is cached, either in
> memory or on
> an L2 ssd, but I need to rerun some tests.
>
> For now the machine seems to be stable with nfsd limited to a single
> thread.
>
>
> Any help debugging would be appreciated,
> Rafi
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