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SubjectRe: preempt bug in set_pmd_pfn?

* Jeremy Fitzhardinge <jeremy@goop.org> wrote:

> Ingo Molnar wrote:
>> * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>>
>>
>>> I think set_pmd_pfn, which is only called by __set_fixmap, might have a
>>> preempt bug in it.
>>>
>>
>> yes, and we had similar preemption bugs in the past. I guess most places
>> are either infrequent or have some natural atomicity anyway. Wanna send a
>> patch?
>
> Sure. Should it just disable preemption, or take a lock? It calls
> set_pte_at without holding any pte locks; that seems to be relatively
> common. Is it OK when you're operating on init_mm?

no, it's not OK to modify the kernel pagetable without locking - taking
the pgd_lock should do the trick. Could you send the stacktrace that
shows the place that is preemptible?

Ingo


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