1 files changed, 58 insertions, 13 deletions

diff --git a/mm/memory.c b/mm/memory.c
index b6e5fd23cc5a..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);
@@ -2756,25 +2783,43 @@ out_page:
         unlock_page(page);
 out_release:
         page_cache_release(page);
+        if (swapcache) {
+                unlock_page(swapcache);
+                page_cache_release(swapcache);
+        }
         return ret;
 }
 
 /*
- * This is like a special single-page "expand_downwards()",
- * except we must first make sure that 'address-PAGE_SIZE'
+ * This is like a special single-page "expand_{down|up}wards()",
+ * except we must first make sure that 'address{-|+}PAGE_SIZE'
  * doesn't hit another vma.
- *
- * The "find_vma()" will do the right thing even if we wrap
  */
 static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned long address)
 {
         address &= PAGE_MASK;
         if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
-                address -= PAGE_SIZE;
-                if (find_vma(vma->vm_mm, address) != vma)
-                        return -ENOMEM;
+                struct vm_area_struct *prev = vma->vm_prev;
+
+                /*
+                 * Is there a mapping abutting this one below?
+                 *
+                 * That's only ok if it's the same stack mapping
+                 * that has gotten split..
+                 */
+                if (prev && prev->vm_end == address)
+                        return prev->vm_flags & VM_GROWSDOWN ? 0 : -ENOMEM;
+
+                expand_stack(vma, address - PAGE_SIZE);
+        }
+        if ((vma->vm_flags & VM_GROWSUP) && address + PAGE_SIZE == vma->vm_end) {
+                struct vm_area_struct *next = vma->vm_next;
+
+                /* As VM_GROWSDOWN but s/below/above/ */
+                if (next && next->vm_start == address + PAGE_SIZE)
+                        return next->vm_flags & VM_GROWSUP ? 0 : -ENOMEM;
 
-                expand_stack(vma, address);
+                expand_upwards(vma, address + PAGE_SIZE);
         }
         return 0;
 }