Linux-libre 4.6.2-gnu

1 files changed, 19 insertions, 8 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index ca6d2a06a..4786b4150 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -352,13 +352,17 @@ static inline bool ksm_test_exit(struct mm_struct *mm)
 /*
  * We use break_ksm to break COW on a ksm page: it's a stripped down
  *
- *	if (get_user_pages(current, mm, addr, 1, 1, 1, &page, NULL) == 1)
+ *	if (get_user_pages(addr, 1, 1, 1, &page, NULL) == 1)
  *		put_page(page);
  *
  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
  * in case the application has unmapped and remapped mm,addr meanwhile.
  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
+ *
+ * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
+ * of the process that owns 'vma'.  We also do not want to enforce
+ * protection keys here anyway.
  */
 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 {
@@ -367,12 +371,14 @@ static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
 
 	do {
 		cond_resched();
-		page = follow_page(vma, addr, FOLL_GET | FOLL_MIGRATION);
+		page = follow_page(vma, addr,
+				FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
 		if (IS_ERR_OR_NULL(page))
 			break;
 		if (PageKsm(page))
 			ret = handle_mm_fault(vma->vm_mm, vma, addr,
-							FAULT_FLAG_WRITE);
+							FAULT_FLAG_WRITE |
+							FAULT_FLAG_REMOTE);
 		else
 			ret = VM_FAULT_WRITE;
 		put_page(page);
@@ -777,6 +783,7 @@ static int unmerge_and_remove_all_rmap_items(void)
 		}
 
 		remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
+		up_read(&mm->mmap_sem);
 
 		spin_lock(&ksm_mmlist_lock);
 		ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
@@ -788,12 +795,9 @@ static int unmerge_and_remove_all_rmap_items(void)
 
 			free_mm_slot(mm_slot);
 			clear_bit(MMF_VM_MERGEABLE, &mm->flags);
-			up_read(&mm->mmap_sem);
 			mmdrop(mm);
-		} else {
+		} else
 			spin_unlock(&ksm_mmlist_lock);
-			up_read(&mm->mmap_sem);
-		}
 	}
 
 	/* Clean up stable nodes, but don't worry if some are still busy */
@@ -1657,8 +1661,15 @@ next_mm:
 		up_read(&mm->mmap_sem);
 		mmdrop(mm);
 	} else {
-		spin_unlock(&ksm_mmlist_lock);
 		up_read(&mm->mmap_sem);
+		/*
+		 * up_read(&mm->mmap_sem) first because after
+		 * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
+		 * already have been freed under us by __ksm_exit()
+		 * because the "mm_slot" is still hashed and
+		 * ksm_scan.mm_slot doesn't point to it anymore.
+		 */
+		spin_unlock(&ksm_mmlist_lock);
 	}
 
 	/* Repeat until we've completed scanning the whole list */