NFS-exported ZFS instability

[Hiroki Sato]

Konstantin Belousov <kostikbel at gmail.com> wrote
  in <20130102174044.GB82219 at kib.kiev.ua>:

ko> > I might take a closer look this evening and see if I can spot anything
ko> > in the log, rick
ko> > ps: I hope Alan and Kostik don't mind being added to the cc list.
ko>
ko> What I see in the log is that the lock cascade rooted in the thread
ko> 100838, which owns system map mutex. I believe this prevents malloc(9)
ko> from making a progress in other threads, which e.g. own the ZFS vnode
ko> locks. As the result, the whole system wedged.
ko>
ko> Looking back at the thread 100838, we can see that it executes
ko> smp_tlb_shootdown(). It is impossible to tell from the static dump,
ko> is the appearance of the smp_tlb_shootdown() in the backtrace is
ko> transient, or the thread is spinning there, waiting for other CPUs to
ko> acknowledge the request. But, since the system wedged, most likely,
ko> smp_tlb_shootdown spins.
ko>
ko> Taking this hypothesis, the situation can occur, most likely, due to
ko> some other core running with the interrupts disabled. Inspection of the
ko> backtraces of the processes running on all cores does not show any which
ko> could legitimately own a spinlock or otherwise run with the interrupts
ko> disabled.
ko>
ko> One thing you could try to do is to enable WITNESS for the spinlocks,
ko> to try to catch the leaked spinlock. I very much doubt that this is
ko> the case.
ko>
ko> Another thing to try is to switch the CPU idle method to something
ko> else. Look at the machdep.idle* sysctls. It could be some CPU errata
ko> which blocks wakeup due the interrupt in some conditions in C1 ?

 Thank you.  It can take 1-2 weeks to reproduce this, so I set
 debug.witness.skipspin=0 and keeping machdep.idle acpi abd will see
 how it goes for a while.  I will report again if I can get another
 freeze.

-- Hiroki
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