1 files changed, 25 insertions, 1 deletions

diff --git a/mm/memory.c b/mm/memory.c
index bbab1e37055e..fb5608a120ed 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -311,6 +311,21 @@ int __pte_alloc(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
         if (!new)
                 return -ENOMEM;
 
+        /*
+         * Ensure all pte setup (eg. pte page lock and page clearing) are
+         * visible before the pte is made visible to other CPUs by being
+         * put into page tables.
+         *
+         * The other side of the story is the pointer chasing in the page
+         * table walking code (when walking the page table without locking;
+         * ie. most of the time). Fortunately, these data accesses consist
+         * of a chain of data-dependent loads, meaning most CPUs (alpha
+         * being the notable exception) will already guarantee loads are
+         * seen in-order. See the alpha page table accessors for the
+         * smp_read_barrier_depends() barriers in page table walking code.
+         */
+        smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
+
         spin_lock(&mm->page_table_lock);
         if (!pmd_present(*pmd)) {       /* Has another populated it ? */
                 mm->nr_ptes++;
@@ -329,6 +344,8 @@ int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
         if (!new)
                 return -ENOMEM;
 
+        smp_wmb(); /* See comment in __pte_alloc */
+
         spin_lock(&init_mm.page_table_lock);
         if (!pmd_present(*pmd)) {       /* Has another populated it ? */
                 pmd_populate_kernel(&init_mm, pmd, new);
@@ -969,7 +986,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                 goto no_page_table;
         
         pmd = pmd_offset(pud, address);
-        if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+        if (pmd_none(*pmd))
                 goto no_page_table;
 
         if (pmd_huge(*pmd)) {
@@ -978,6 +995,9 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
                 goto out;
         }
 
+        if (unlikely(pmd_bad(*pmd)))
+                goto no_page_table;
+
         ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
         if (!ptep)
                 goto out;
@@ -2616,6 +2636,8 @@ int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
         if (!new)
                 return -ENOMEM;
 
+        smp_wmb(); /* See comment in __pte_alloc */
+
         spin_lock(&mm->page_table_lock);
         if (pgd_present(*pgd))          /* Another has populated it */
                 pud_free(mm, new);
@@ -2637,6 +2659,8 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
         if (!new)
                 return -ENOMEM;
 
+        smp_wmb(); /* See comment in __pte_alloc */
+
         spin_lock(&mm->page_table_lock);
 #ifndef __ARCH_HAS_4LEVEL_HACK
         if (pud_present(*pud))          /* Another has populated it */