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SubjectRe: [local DoS] Re: Linux 2.6.24-rc4

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

>
>
> On Tue, 4 Dec 2007, Luiz Fernando N. Capitulino wrote:
> >
> > sched_rr_get_interval(1, NULL);
>
> Looks like we have a zero "cfs_rq->load.weight".
>
> Ingo? Both sched_slice() and __sched_slice() do a divide by the
> runqueue weight, and at least dequeue_task_fair() explicitly checks
> for that being zero, so clearly zero is a possible value. Hmm?

yeah, i can reproduce this crash too.

The problem is on SMP: if sched_rr_get_interval() gets a task from an
otherwise idle runqueue, then rq->load.weight is 0. Normally
sched_slice() is only used on a busy runqueue. So the correct fixup site
is not in sched_slice() but in sys_sched_rr_get_interval() - i'm working
on the right fix, i hope to be able to send a pull request in a few
minutes.

Ingo


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