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Cc: freebsd-hackers@freebsd.org
Subject: Re: sched_pin() versus PCPU_GET
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On Thursday, August 05, 2010 12:01:22 pm mdf@freebsd.org wrote:
> On Wed, Aug 4, 2010 at 9:20 AM,  <mdf@freebsd.org> wrote:
> > On Wed, Aug 4, 2010 at 2:26 PM, John Baldwin <jhb@freebsd.org> wrote:
> >> Actually, I would beg to differ in that case.  If PCPU_GET(spinlocks)
> >> returns non-NULL, then it means that you hold a spin lock,
> >
> > ll_count is 0 for the "correct" pc_spinlocks and non-zero for the
> > "wrong" one, though.  So I think it can be non-NULL but the current
> > thread/CPU doesn't hold a spinlock.
> >
> > I don't believe we have any code in the NMI handler.  I'm on vacation
> > today so I'll check tomorrow.
> 
> I checked and ipi_nmi_handler() doesn't appear to have any local
> changes.  I assume that's where I should look?

The tricky bits are all in the assembly rather than in C, probably in 
exception.S.  However, if %gs were corrupt I would not expect it to point to 
another CPU's data, but garbage from userland.

-- 
John Baldwin