Daily panic in getnewvnode

[Greg 'groggy' Lehey]

For the last month I've been getting a daily panic out of getvnode.  A
brief summary:

- Panic message is "Cleaned vnode isn't".  This means that the vnode
  pulled off the free list and cleaned with vtryrecycle still has the
  vp->v_data field set.
- It happens during the nightly cron jobs.
- The program in question is find, going through a large disk (200 GB,
  several million files).
- The disk does not seem to be getting fsck'd.
- The test in question is part of the INVARIANTS checking code, so if
  I turned INVARIANTS off, the panic would no longer occur.

I suspect that if I ran fsck on the disk, it would also solve the
problem.  The reason I haven't done so is because I chose this
particular panic to document for my next kernel debugging tutorial.
Unfortunately, I'm running out of time, and I'd really like to find
the *real* cause of this bug.  If anybody's seen anything like this,
please let me know.  I have a draft of my tutorial notes at
http://www.lemis.com/grog/handout.pdf, and the description starts on
page 86.  If anybody can help me clarify the problem, I'd be very
grateful.

Greg
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