1 files changed, 36 insertions, 5 deletions

diff --git a/mm/memory.c b/mm/memory.c
index 6b2ab1051851..0e18b4d649ec 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2623,7 +2623,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 unsigned int flags, pte_t orig_pte)
 {
         spinlock_t *ptl;
-        struct page *page;
+        struct page *page, *swapcache = NULL;
         swp_entry_t entry;
         pte_t pte;
         struct mem_cgroup *ptr = NULL;
@@ -2679,10 +2679,25 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         lock_page(page);
         delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
 
-        page = ksm_might_need_to_copy(page, vma, address);
-        if (!page) {
-                ret = VM_FAULT_OOM;
-                goto out;
+        /*
+         * Make sure try_to_free_swap or reuse_swap_page or swapoff did not
+         * release the swapcache from under us.  The page pin, and pte_same
+         * test below, are not enough to exclude that.  Even if it is still
+         * swapcache, we need to check that the page's swap has not changed.
+         */
+        if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val))
+                goto out_page;
+
+        if (ksm_might_need_to_copy(page, vma, address)) {
+                swapcache = page;
+                page = ksm_does_need_to_copy(page, vma, address);
+
+                if (unlikely(!page)) {
+                        ret = VM_FAULT_OOM;
+                        page = swapcache;
+                        swapcache = NULL;
+                        goto out_page;
+                }
         }
 
         if (mem_cgroup_try_charge_swapin(mm, page, GFP_KERNEL, &ptr)) {
@@ -2735,6 +2750,18 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
                 try_to_free_swap(page);
         unlock_page(page);
+        if (swapcache) {
+                /*
+                 * Hold the lock to avoid the swap entry to be reused
+                 * until we take the PT lock for the pte_same() check
+                 * (to avoid false positives from pte_same). For
+                 * further safety release the lock after the swap_free
+                 * so that the swap count won't change under a
+                 * parallel locked swapcache.
+                 */
+                unlock_page(swapcache);
+                page_cache_release(swapcache);
+        }
 
         if (flags & FAULT_FLAG_WRITE) {
                 ret |= do_wp_page(mm, vma, address, page_table, pmd, ptl, pte);
@@ -2756,6 +2783,10 @@ out_page:
         unlock_page(page);
 out_release:
         page_cache_release(page);
+        if (swapcache) {
+                unlock_page(swapcache);
+                page_cache_release(swapcache);
+        }
         return ret;
 }