(ZFS?): panic: lockmgr: locking against myself

[Peter Schuller]

> I *think* I just experienced the same problem on 7.0-BETA3, except the
> kernel does not have WITNESS/INVARIANTS so I just get a hack instead of a
> panic. I wanted to post with the information I have for completeness; I
> realize what follows is a bunch of anecdotal mumbo-jumbo.

So I can now confirm this problem on 7.0-RC1 on the machine where I originally 
saw this happen.

If I could trigger this in a debuggable environment I would try to get some 
much more interesting information, but as this was during time-limited access 
to the machine in a noisy colocation facility, with people waiting on the 
machine to come back up, I was not in a position to do very much. Instead I 
will again, as an added data point, provide an approximate timeline below. As 
previously observed, it seems to be triggered by changes in the availability 
of disks and/or zpool configuration, with cold reboots somehow mitigating the 
problem.

Note that the drives are likely to have been moved around a bit logically (but 
not physically), due to the level of indirection and drive number allocation 
resulting from the single-disk raid0 virtual hardware raid device.

Timeline:

* Machine running 7-CURRENT from the october/september era.

* One disk in a three-way zfs mirror (tank, on which root fs is) gets kicked 
out.

* For probably unrelated reasons, the machine crashes with a kmem_alloc error 
(this was the first time ever on this machine). Don't have details; this was 
observed by colocation personel.

* Machine rebooted and panic:s as described in this thread.

* I arrive on-site and reboot again just for kicks. Same problem.

* I physically remove the broken disk and replace it with the new one, and add 
the virtual disk in the RAID controller bios (recap: this is a Dell 2950).

* Now it boots again.

* I zpool replace tank label/tank3 label/tank3r1 (after various 
disklabel/glabel action).

* make installkernell (7.0-RC1)

* Reboot with resilvering/replacement still in progress.

* Panic on boot.

* Tried cold reboot (turn off,turn on) -> it now boots again without a panic.

* Make installworld.

* At this point I no longer remember whether it booted again or whether I had 
to do another cold reboot.

* Machine has not been rebooted again since resilvering completed.

-- 
/ Peter Schuller

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