Hugh Dickins <hughd@xxxxxxxxxx> writes:
> Swapoff after swapping hangs on the G5. That's because the _PAGE_PTE
> bit, added by set_pte_at(), is not expected by swapoff: so swap ptes
> cannot be recognized.
>
> I'm not sure whether a swap pte should or should not have _PAGE_PTE set:
> this patch assumes not, and fixes set_pte_at() to set _PAGE_PTE only on
> present entries.
One of the reason we added _PAGE_PTE is to enable HUGETLB migration. So
we want migratio ptes to have _PAGE_PTE set.
>
> But if that's wrong, a reasonable alternative would be to
> #define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) & ~_PAGE_PTE })
> #define __swp_entry_to_pte(x) __pte((x).val | _PAGE_PTE)
>
We do clear _PAGE_PTE bits, when converting swp_entry_t to type and
offset. Can you share the stack trace for the hang, which will help me
understand this more ? .
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
>
> arch/powerpc/mm/pgtable.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> --- 4.4-next/arch/powerpc/mm/pgtable.c 2016-01-06 11:54:01.477512251 -0800
> +++ linux/arch/powerpc/mm/pgtable.c 2016-01-09 13:51:15.793485717 -0800
> @@ -180,9 +180,10 @@ void set_pte_at(struct mm_struct *mm, un
> VM_WARN_ON((pte_val(*ptep) & (_PAGE_PRESENT | _PAGE_USER)) ==
> (_PAGE_PRESENT | _PAGE_USER));
> /*
> - * Add the pte bit when tryint set a pte
> + * Add the pte bit when setting a pte (not a swap entry)
> */
> - pte = __pte(pte_val(pte) | _PAGE_PTE);
> + if (pte_val(pte) & _PAGE_PRESENT)
> + pte = __pte(pte_val(pte) | _PAGE_PTE);
>
> /* Note: mm->context.id might not yet have been assigned as
> * this context might not have been activated yet when this
-aneesh
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