Re: preempt bug in set_pmd_pfn?

[Ingo Molnar]

* Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:

> Ingo Molnar wrote:
>> * Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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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