panic: spin lock held too long (RELENG_8 from today)

[Hiroki Sato]

Chip Camden <sterling at camdensoftware.com> wrote
  in <20110818025550.GA1971 at libertas.local.camdensoftware.com>:

st> Quoth Attilio Rao on Thursday, 18 August 2011:
st> > In callout_cpu_switch() if a low priority thread is migrating the
st> > callout and gets preempted after the outcoming cpu queue lock is left
st> > (and scheduled much later) we get this problem.
st> >
st> > In order to fix this bug it could be enough to use a critical section,
st> > but I think this should be really interrupt safe, thus I'd wrap them
st> > up with spinlock_enter()/spinlock_exit(). Fortunately
st> > callout_cpu_switch() should be called rarely and also we already do
st> > expensive locking operations in callout, thus we should not have
st> > problem performance-wise.
st> >
st> > Can the guys I also CC'ed here try the following patch, with all the
st> > initial kernel options that were leading you to the deadlock? (thus
st> > revert any debugging patch/option you added for the moment):
st> > http://www.freebsd.org/~attilio/callout-fixup.diff
st> >
st> > Please note that this patch is for STABLE_8, if you can confirm the
st> > good result I'll commit to -CURRENT and then backmarge as soon as
st> > possible.
st> >
st> > Thanks,
st> > Attilio
st> >
st>
st> Thanks, Attilio.  I've applied the patch and removed the extra debug
st> options I had added (though keeping debug symbols).  I'll let you know if
st> I experience any more panics.

 No panic for 20 hours at this moment, FYI.  For my NFS server, I
 think another 24 hours would be sufficient to confirm the stability.
 I will see how it works...

-- Hiroki
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