Re: 2.6.38-rc1 problems with khugepaged

[Steven Rostedt]

On Wed, Jan 19, 2011 at 11:21:50PM +0100, Andrea Arcangeli wrote:
> Hello Werner,
> 
> this should fix your oops, it's untested still so let me know if you
> test it.

I tested this with ktest.pl on the config that was breaking for me. I
ran the test 20 times and it succeeded for all 20 tests.

Tested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>

-- Steve


> 
> It's a noop for x86_64 and it only affected x86 32bit with highpte enabled.
> 
> ====
> Subject: khugepaged: fix pte_unmap for highpte x86_32
> 
> From: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> 
> __collapse_huge_page_copy is still dereferencing the pte passed as parameter so
> we must pte_unmap after __collapse_huge_page_copy returns, not before.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> ---
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 004c9c2..c4f634b 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1837,9 +1837,9 @@ static void collapse_huge_page(struct mm_struct *mm,
>  	spin_lock(ptl);
>  	isolated = __collapse_huge_page_isolate(vma, address, pte);
>  	spin_unlock(ptl);
> -	pte_unmap(pte);
>  
>  	if (unlikely(!isolated)) {
> +		pte_unmap(pte);
>  		spin_lock(&mm->page_table_lock);
>  		BUG_ON(!pmd_none(*pmd));
>  		set_pmd_at(mm, address, pmd, _pmd);
> @@ -1856,6 +1856,7 @@ static void collapse_huge_page(struct mm_struct *mm,
>  	anon_vma_unlock(vma->anon_vma);
>  
>  	__collapse_huge_page_copy(pte, new_page, vma, address, ptl);
> +	pte_unmap(pte);
>  	__SetPageUptodate(new_page);
>  	pgtable = pmd_pgtable(_pmd);
>  	VM_BUG_ON(page_count(pgtable) != 1);
> 
> 
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