mm: change mm_update_next_owner() to update mm->owner with WRITE_ONCE

euler inclusion
category: bugfix
bugzilla: 10989
CVE: NA

------------------------------------------------

The RCU reader uses rcu_dereference() inside rcu_read_lock critical
sections, so the writer shall use WRITE_ONCE. Just a cleanup, we still
rely on gcc to emit atomic writes in other places.
Signed-off-by: NAndrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Nzhong jiang <zhongjiang@huawei.com>
Reviewed-by: NJing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

kernel/exit.c

@@ -422,7 +422,7 @@ void mm_update_next_owner(struct mm_struct *mm)
 	 * freed task structure.
 	 */
 	if (atomic_read(&mm->mm_users) <= 1) {
-		mm->owner = NULL;
+		WRITE_ONCE(mm->owner, NULL);
 		return;
 	}
 
@@ -462,7 +462,7 @@ void mm_update_next_owner(struct mm_struct *mm)
 	 * most likely racing with swapoff (try_to_unuse()) or /proc or
 	 * ptrace or page migration (get_task_mm()).  Mark owner as NULL.
 	 */
-	mm->owner = NULL;
+	WRITE_ONCE(mm->owner, NULL);
 	return;
 
 assign_new_owner:
@@ -483,7 +483,7 @@ void mm_update_next_owner(struct mm_struct *mm)
 		put_task_struct(c);
 		goto retry;
 	}
-	mm->owner = c;
+	WRITE_ONCE(mm->owner, c);
 	task_unlock(c);
 	put_task_struct(c);
 }

kernel/fork.c

@@ -961,7 +961,7 @@ static __always_inline void mm_clear_owner(struct mm_struct *mm,
 {
 #ifdef CONFIG_MEMCG
 	if (mm->owner == p)
-		mm->owner = NULL;
+		WRITE_ONCE(mm->owner, NULL);
 #endif
 }