Re: [PATCH] kthreads: Fix startup synchronization boot crash

[Ingo Molnar]

* Oleg Nesterov <oleg@xxxxxxxxxx> wrote:

> On 09/01, Ingo Molnar wrote:
> >
> > * Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> >
> > > But I must admit, now I don't understand what happens,
> > >
> > > 	The modification of that variable is protected by the BKL, but
> > > 	the _ordering_ of the initial task (which becomes the idle
> > > 	thread of CPU0) and the init task (which is spawned by the
> > > 	initial task) is not synchronized.
> > >
> > > 	So we can occasionally end up init running sooner than
> > > 	rest_init()
> > >
> > > How? rest_init() can't be preempted and it holds BKL. And
> > > kernel_init() takes BKL before anything else. Confused...
> >
> > it cannot be preempted but it can schedule anywhere - and the BKL
> > will be dropped silently.
> >
> > This is one of the biggest dangers of the BKL
> 
> Yes I see. But rest_init() runs under preempt_disable(). If it was 
> rescheduled, schedule_debug() should complain. No?

hm, either something is broken, or some other codepath learned to do 
preempt_enable() in early init ... [which i'd call broken too]

Weird.

	Ingo
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