svn commit: r211176 - in head/sys: amd64/amd64 i386/i386

[Kostik Belousov]

On Wed, Aug 11, 2010 at 01:21:46PM +0200, Attilio Rao wrote:
> 2010/8/11 Kostik Belousov <kostikbel at gmail.com>:
> > On Wed, Aug 11, 2010 at 10:51:27AM +0000, Attilio Rao wrote:
> >> Author: attilio
> >> Date: Wed Aug 11 10:51:27 2010
> >> New Revision: 211176
> >> URL: http://svn.freebsd.org/changeset/base/211176
> >>
> >> Log:
> >>   IPI handlers may run generally with interrupts disabled because they
> >>   are served via an interrupt gate.
> >>
> >>   However, that doesn't explicitly prevent preemption and thread
> >>   migration thus scheduler pinning may be necessary in some handlers.
> >>   Fix that.
> >
> > How the preemption is supposed to happen ? Aside from the explicit
> > calls to mi_switch() from e.g. critical_exit().
> 
> IIRC it should be hardclock() willing to schedule the softclock(). It
> is the critical_exit() in the thread_unlock() that may trigger it
> (sorry for not digging more, it was a while back that I hacked this
> part, but I guess you can verify on your own).
> We already have other points within the kernel that take care of
> dealing with preemption/migration like lapic_handle_timer(), for
> example.

Right, and if the interrupts are indeed disabled, I do not see how
the preemption may be triggered in the fragments like
	cpu = PCPU_GET(cpuid);
	cpumask = PCPU_GET(cpumask);
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