Re: hugetlbfs for ppc440 - kernel BUG -- follow up

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Tue, 2007-07-17 at 16:07 -0500, Satya wrote:
> hello,
> 
> Upon investigating the below issue further, I found that
> pte_alloc_map() calls kmap_atomic. The allocated pte page must be
> unmapped before invoking any function that might_sleep.
> 
> In this case clear_huge_page() is being called without invoking
> pte_unmap(). The 'normal' counterpart of hugetlb_no_page (which is
> do_no_page() in mm/memory.c) does call pte_unmap() before calling
> alloc_page() (which might sleep).
> 
> So, I believe pte_unmap() must be invoked first in hugetlb_no_page().
> But the problem here is, we do not have a reference to the pmd to map
> the pte again (using pte_offset_map()). The do_no_page() function does
> have a pmd_t* parameter, so it can remap the pte when required.
> 
> For now, I resolved the problem by expanding the pte_alloc_map() macro
> by hand and replacing kmap_atomic with kmap(), although I think it is
> not the right thing to do.
> 
> Let me know if my analysis is helping you figure out the problem here. Thanks!

Except that I don't see where pte_alloc_map() has been called before
hand... hugetlb_no_page() is called by hugetlb_fault() which is called
by __handle_mm_fault(), with no lock held.

Ben.