On Sun, 27 Nov 2005, Eric W. Biederman wrote:
> Andi Kleen <[email protected]> writes:
>
> > On Sun, Nov 27, 2005 at 02:05:45AM -0800, Zwane Mwaikambo wrote:
> >> http://bugzilla.kernel.org/show_bug.cgi?id=5203
> >>
> >> There is a small race during SMP shutdown between the processor issuing
> >> the shutdown and the other processors clearing themselves off the
> >> cpu_online_map as they do this without using the normal cpu offline
> >> synchronisation. To avoid this we should wait for all the other processors
> >> to clear their corresponding bits and then proceed. This way we can safely
> >> make the cpu_online test in smp_send_reschedule, it's safe during normal
> >> runtime as smp_send_reschedule is called with a lock held / preemption
> >> disabled.
> >
> > Looking at the backtrace in the bug - how can sys_reboot call do_exit???
> > I would say the problem is in whatever causes that. It shouldn't
> > do that. sys_reboot shouldn't schedule, it's that simple.
> > Your patch is just papering over that real bug.
>
> sys_reboot in the case of halt (after everything else is done)
> has directly called do_exit for years.
>
> There are some very subtle interactions there. The one
> I always remember (having found it the hard way) is that
> interrupts must be left on so ctrl-alt-del still works.
>
> This do_exit may be something similar, although I can't
> think of how it could be useful.
I wondered the same thing, perhaps i am papering over the bug, what
exactly is do_exit doing there?
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