hugetlb: clarify hugetlb_instantiation_mutex usage

[platform/adaptation/renesas_rcar/renesas_kernel.git] / mm / hugetlb.c

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 7acd125..49e693b 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2349,6 +2349,9 @@ static int unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 
 /*
  * Hugetlb_cow() should be called with page lock of the original hugepage held.
+ * Called with hugetlb_instantiation_mutex held and pte_page locked so we
+ * cannot race with other handlers or page migration.
+ * Keep the pte_same checks anyway to make transition from the mutex easier.
  */
 static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
                        unsigned long address, pte_t *ptep, pte_t pte,
@@ -2408,7 +2411,14 @@ retry_avoidcopy:
                                BUG_ON(page_count(old_page) != 1);
                                BUG_ON(huge_pte_none(pte));
                                spin_lock(&mm->page_table_lock);
-                               goto retry_avoidcopy;
+                               ptep = huge_pte_offset(mm, address & huge_page_mask(h));
+                               if (likely(pte_same(huge_ptep_get(ptep), pte)))
+                                       goto retry_avoidcopy;
+                               /*
+                                * race occurs while re-acquiring page_table_lock, and
+                                * our job is done.
+                                */
+                               return 0;
                        }
                        WARN_ON_ONCE(1);
                }