mm/THP: use pmd_populate() to update the pmd with pgtable_t pointer
Aneesh Kumar K.V [Fri, 24 May 2013 22:55:21 +0000 (15:55 -0700)]
We should not use set_pmd_at to update pmd_t with pgtable_t pointer.
set_pmd_at is used to set pmd with huge pte entries and architectures
like ppc64, clear few flags from the pte when saving a new entry.
Without this change we observe bad pte errors like below on ppc64 with
THP enabled.

  BUG: Bad page map in process ld mm=0xc000001ee39f4780 pte:7fc3f37848000001 pmd:c000001ec0000000

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/huge_memory.c

index 03a89a2..362c329 100644 (file)
@@ -2325,7 +2325,12 @@ static void collapse_huge_page(struct mm_struct *mm,
                pte_unmap(pte);
                spin_lock(&mm->page_table_lock);
                BUG_ON(!pmd_none(*pmd));
-               set_pmd_at(mm, address, pmd, _pmd);
+               /*
+                * We can only use set_pmd_at when establishing
+                * hugepmds and never for establishing regular pmds that
+                * points to regular pagetables. Use pmd_populate for that
+                */
+               pmd_populate(mm, pmd, pmd_pgtable(_pmd));
                spin_unlock(&mm->page_table_lock);
                anon_vma_unlock_write(vma->anon_vma);
                goto out;