Re: [patch 3/3] mm: fault handler to replace nopage and populate

Thomas Hellström
2006-10-10T06:11:27Z

Benjamin Herrenschmidt wrote:

>
>>>Could it be an option to make it safe for the fault handler to
>>>temporarily drop the mmap_sem read lock given that some conditions TBD
>>>are met?
>>>In that case it can retake the mmap_sem write lock, do the VMA flags
>>>modifications, downgrade and do the pte modifications using a helper, or
>>>even use remap_pfn_range() during the time the write lock is held?
>>>
>>>
>>When you drop and retake the mmap_sem, you need to start again from
>>find_vma. At which point you technically probably want to start again
>>from the architecture specfic fault code. It sounds difficult but I
>>won't say it can't be done.
>>
>>
>
>I can be done with returning NOPAGE_REFAULT but as you said, I don't
>think it's necessary.
>
>
Still, even with NOPAGE_REFAULT or the equivalent with the new fault() code,
in the case we need to take this route, (and it looks like we won't have
to),
I guess we still need to restart from find_vma() in the fault()/nopage()
handler to make sure the VMA is still present. The object mutex need to
be dropped as well to avoid deadlocks. Sounds complicated.

>Cheers,
>Ben.
>
>
>
>
/Thomas