Messages in this thread | | | Date | Wed, 2 Sep 2009 15:06:44 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] kthreads: Fix startup synchronization boot crash |
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* Oleg Nesterov <oleg@redhat.com> wrote:
> On 09/01, Ingo Molnar wrote: > > > > * Oleg Nesterov <oleg@redhat.com> 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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