@@ -12,6 +12,7 @@
  #include <linux/sched.h>
  #include <linux/proc_fs.h>
  struct  ctl_table_header;
+struct  mempolicy;
  
  extern struct proc_dir_entry proc_root;
  #ifdef CONFIG_PROC_SYSCTL

@@ -74,6 +75,9 @@ struct proc_maps_private {
  #ifdef CONFIG_MMU
  	struct vm_area_struct *tail_vma;
  #endif
+#ifdef CONFIG_NUMA
+	struct mempolicy *task_mempolicy;
+#endif
  };
  
  void proc_init_inodecache(void);

@@ -89,11 +89,55 @@ static void pad_len_spaces(struct seq_file *m, int len)
  		len = 1;
  	seq_printf(m, "%*c", len, ' ');
  }
+#ifdef CONFIG_NUMA
+/*
+ * These functions are for numa_maps but called in generic **maps seq_file
+ * ->start(), ->stop() ops.
+ *
+ * numa_maps scans all vmas under mmap_sem and checks their mempolicy.
+ * Each mempolicy object is controlled by reference counting. The problem here
+ * is how to avoid accessing dead mempolicy object.
+ *
+ * Because we're holding mmap_sem while reading seq_file, it's safe to access
+ * each vma's mempolicy, no vma objects will never drop refs to mempolicy.
+ *
+ * A task's mempolicy (task->mempolicy) has different behavior. task->mempolicy
+ * is set and replaced under mmap_sem but unrefed and cleared under task_lock().
+ * So, without task_lock(), we cannot trust get_vma_policy() because we cannot
+ * gurantee the task never exits under us. But taking task_lock() around
+ * get_vma_plicy() causes lock order problem.
+ *
+ * To access task->mempolicy without lock, we hold a reference count of an
+ * object pointed by task->mempolicy and remember it. This will guarantee
+ * that task->mempolicy points to an alive object or NULL in numa_maps accesses.
+ */
+static void hold_task_mempolicy(struct proc_maps_private *priv)
+{
+	struct task_struct *task = priv->task;
+
+	task_lock(task);
+	priv->task_mempolicy = task->mempolicy;
+	mpol_get(priv->task_mempolicy);
+	task_unlock(task);
+}
+static void release_task_mempolicy(struct proc_maps_private *priv)
+{
+	mpol_put(priv->task_mempolicy);
+}
+#else
+static void hold_task_mempolicy(struct proc_maps_private *priv)
+{
+}
+static void release_task_mempolicy(struct proc_maps_private *priv)
+{
+}
+#endif
  
  static void vma_stop(struct proc_maps_private *priv, struct vm_area_struct *vma)
  {
  	if (vma && vma != priv->tail_vma) {
  		struct mm_struct *mm = vma->vm_mm;
+		release_task_mempolicy(priv);
  		up_read(&mm->mmap_sem);
  		mmput(mm);
  	}

@@ -132,7 +176,7 @@ static void *m_start(struct seq_file *m, loff_t *pos)
  
  	tail_vma = get_gate_vma(priv->task->mm);
  	priv->tail_vma = tail_vma;
-
+	hold_task_mempolicy(priv);
  	/* Start with last addr hint */
  	vma = find_vma(mm, last_addr);
  	if (last_addr && vma) {

@@ -159,6 +203,7 @@ out:
  	if (vma)
  		return vma;
  
+	release_task_mempolicy(priv);
  	/* End of vmas has been reached */
  	m->version = (tail_vma != NULL)? 0: -1UL;
  	up_read(&mm->mmap_sem);

@@ -1178,11 +1223,9 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
  	walk.private = md;
  	walk.mm = mm;
  
-	task_lock(task);
  	pol = get_vma_policy(task, vma, vma->vm_start);
  	mpol_to_str(buffer, sizeof(buffer), pol, 0);
  	mpol_cond_put(pol);
-	task_unlock(task);
  
  	seq_printf(m, "%08lx %s", vma->vm_start, buffer);