Merge tag 'v4.5-rc7' into x86/asm, to pick up SMAP fix

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 38090ca37a08..906d8e3b42c0 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3425,8 +3425,18 @@ static int __handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
         if (unlikely(pmd_none(*pmd)) &&
             unlikely(__pte_alloc(mm, vma, pmd, address)))
                 return VM_FAULT_OOM;
-        /* if an huge pmd materialized from under us just retry later */
-        if (unlikely(pmd_trans_huge(*pmd) || pmd_devmap(*pmd)))
+        /*
+         * If a huge pmd materialized under us just retry later.  Use
+         * pmd_trans_unstable() instead of pmd_trans_huge() to ensure the pmd
+         * didn't become pmd_trans_huge under us and then back to pmd_none, as
+         * a result of MADV_DONTNEED running immediately after a huge pmd fault
+         * in a different thread of this mm, in turn leading to a misleading
+         * pmd_trans_huge() retval.  All we have to ensure is that it is a
+         * regular pmd that we can walk with pte_offset_map() and we can do that
+         * through an atomic read in C, which is what pmd_trans_unstable()
+         * provides.
+         */
+        if (unlikely(pmd_trans_unstable(pmd) || pmd_devmap(*pmd)))
                 return 0;
         /*
          * A regular pmd is established and it can't morph into a huge pmd