powerpc: disable assert_pte_locked for collapse_huge_page

With THP we set pmd to none, before we do pte_clear. Hence we can't
walk page table to get the pte lock ptr and verify whether it is locked.
THP do take pte lock before calling pte_clear. So we don't change the locking
rules here. It is that we can't use page table walking to check whether
pte locks are held with THP.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 214130a4edc6..edda589795c3 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -235,6 +235,14 @@ void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
         pud = pud_offset(pgd, addr);
         BUG_ON(pud_none(*pud));
         pmd = pmd_offset(pud, addr);
+        /*
+         * khugepaged to collapse normal pages to hugepage, first set
+         * pmd to none to force page fault/gup to take mmap_sem. After
+         * pmd is set to none, we do a pte_clear which does this assertion
+         * so if we find pmd none, return.
+         */
+        if (pmd_none(*pmd))
+                return;
         BUG_ON(!pmd_present(*pmd));
         assert_spin_locked(pte_lockptr(mm, pmd));
 }