1 files changed, 76 insertions, 24 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 11673c5d2c20..247b5c312b9b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1457,25 +1457,60 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
 {
         struct page *old_page, *new_page;
         pte_t entry;
-        int ret = VM_FAULT_MINOR;
+        int reuse, ret = VM_FAULT_MINOR;
 
         old_page = vm_normal_page(vma, address, orig_pte);
         if (!old_page)
                 goto gotten;
 
-        if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {
-                int reuse = can_share_swap_page(old_page);
-                unlock_page(old_page);
-                if (reuse) {
-                        flush_cache_page(vma, address, pte_pfn(orig_pte));
-                        entry = pte_mkyoung(orig_pte);
-                        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-                        ptep_set_access_flags(vma, address, page_table, entry, 1);
-                        update_mmu_cache(vma, address, entry);
-                        lazy_mmu_prot_update(entry);
-                        ret |= VM_FAULT_WRITE;
-                        goto unlock;
+        if (unlikely((vma->vm_flags & (VM_SHARED|VM_WRITE)) ==
+                                (VM_SHARED|VM_WRITE))) {
+                if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
+                        /*
+                         * Notify the address space that the page is about to
+                         * become writable so that it can prohibit this or wait
+                         * for the page to get into an appropriate state.
+                         *
+                         * We do this without the lock held, so that it can
+                         * sleep if it needs to.
+                         */
+                        page_cache_get(old_page);
+                        pte_unmap_unlock(page_table, ptl);
+
+                        if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
+                                goto unwritable_page;
+
+                        page_cache_release(old_page);
+
+                        /*
+                         * Since we dropped the lock we need to revalidate
+                         * the PTE as someone else may have changed it.  If
+                         * they did, we just return, as we can count on the
+                         * MMU to tell us if they didn't also make it writable.
+                         */
+                        page_table = pte_offset_map_lock(mm, pmd, address,
+                                                         &ptl);
+                        if (!pte_same(*page_table, orig_pte))
+                                goto unlock;
                 }
+
+                reuse = 1;
+        } else if (PageAnon(old_page) && !TestSetPageLocked(old_page)) {
+                reuse = can_share_swap_page(old_page);
+                unlock_page(old_page);
+        } else {
+                reuse = 0;
+        }
+
+        if (reuse) {
+                flush_cache_page(vma, address, pte_pfn(orig_pte));
+                entry = pte_mkyoung(orig_pte);
+                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+                ptep_set_access_flags(vma, address, page_table, entry, 1);
+                update_mmu_cache(vma, address, entry);
+                lazy_mmu_prot_update(entry);
+                ret |= VM_FAULT_WRITE;
+                goto unlock;
         }
 
         /*
@@ -1535,6 +1570,10 @@ oom:
         if (old_page)
                 page_cache_release(old_page);
         return VM_FAULT_OOM;
+
+unwritable_page:
+        page_cache_release(old_page);
+        return VM_FAULT_SIGBUS;
 }
 
 /*
@@ -2083,18 +2122,31 @@ retry:
         /*
          * Should we do an early C-O-W break?
          */
-        if (write_access && !(vma->vm_flags & VM_SHARED)) {
-                struct page *page;
+        if (write_access) {
+                if (!(vma->vm_flags & VM_SHARED)) {
+                        struct page *page;
 
-                if (unlikely(anon_vma_prepare(vma)))
-                        goto oom;
-                page = alloc_page_vma(GFP_HIGHUSER, vma, address);
-                if (!page)
-                        goto oom;
-                copy_user_highpage(page, new_page, address);
-                page_cache_release(new_page);
-                new_page = page;
-                anon = 1;
+                        if (unlikely(anon_vma_prepare(vma)))
+                                goto oom;
+                        page = alloc_page_vma(GFP_HIGHUSER, vma, address);
+                        if (!page)
+                                goto oom;
+                        copy_user_highpage(page, new_page, address);
+                        page_cache_release(new_page);
+                        new_page = page;
+                        anon = 1;
+
+                } else {
+                        /* if the page will be shareable, see if the backing
+                         * address space wants to know that the page is about
+                         * to become writable */
+                        if (vma->vm_ops->page_mkwrite &&
+                            vma->vm_ops->page_mkwrite(vma, new_page) < 0
+                            ) {
+                                page_cache_release(new_page);
+                                return VM_FAULT_SIGBUS;
+                        }
+                }
         }
 
         page_table = pte_offset_map_lock(mm, pmd, address, &ptl);