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Date:      Thu, 5 Aug 2010 19:17:36 +0300
From:      Kostik Belousov <kostikbel@gmail.com>
To:        mdf@freebsd.org
Cc:        freebsd-hackers@freebsd.org
Subject:   Re: sched_pin() versus PCPU_GET
Message-ID:  <20100805161736.GG22295@deviant.kiev.zoral.com.ua>
In-Reply-To: <AANLkTimD6fMLazWwA1bMZZJCKSHdL5v-4kc1wCSVQoMZ@mail.gmail.com>
References:  <AANLkTikY20TxyeyqO5zP3zC-azb748kV-MdevPfm%2B8cq@mail.gmail.com> <201007301031.34266.jhb@freebsd.org> <AANLkTinp7278ZD1L8s616seQET=OQBx1RZ4eHx=e%2BpD5@mail.gmail.com> <201008041026.17553.jhb@freebsd.org> <AANLkTi=YjbBdZp9KuGUmMuYUmWyx_n%2BykikPSMMMo=j9@mail.gmail.com> <AANLkTimD6fMLazWwA1bMZZJCKSHdL5v-4kc1wCSVQoMZ@mail.gmail.com>

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On Thu, Aug 05, 2010 at 09:01:22AM -0700, 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. =9AIf 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. =9ASo 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. =9AI'm on vacation
> > today so I'll check tomorrow.
>=20
> I checked and ipi_nmi_handler() doesn't appear to have any local
> changes.  I assume that's where I should look?

I think that, in case you do not use hwpmc, you could add "iretq"
as the first instruction of the nmi handler in exception.S and see
whether the issue is reproducable.

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