1 files changed, 9 insertions, 24 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index adddf697c4ea..1acec26a3758 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -87,32 +87,14 @@ unsigned long task_statm(struct mm_struct *mm,
 
 #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.
+ * Save get_task_policy() for show_numa_map().
  */
 static void hold_task_mempolicy(struct proc_maps_private *priv)
 {
         struct task_struct *task = priv->task;
 
         task_lock(task);
-        priv->task_mempolicy = task->mempolicy;
+        priv->task_mempolicy = get_task_policy(task);
         mpol_get(priv->task_mempolicy);
         task_unlock(task);
 }
@@ -1431,7 +1413,6 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
         struct vm_area_struct *vma = v;
         struct numa_maps *md = &numa_priv->md;
         struct file *file = vma->vm_file;
-        struct task_struct *task = proc_priv->task;
         struct mm_struct *mm = vma->vm_mm;
         struct mm_walk walk = {};
         struct mempolicy *pol;
@@ -1451,9 +1432,13 @@ static int show_numa_map(struct seq_file *m, void *v, int is_pid)
         walk.private = md;
         walk.mm = mm;
 
-        pol = get_vma_policy(task, vma, vma->vm_start);
-        mpol_to_str(buffer, sizeof(buffer), pol);
-        mpol_cond_put(pol);
+        pol = __get_vma_policy(vma, vma->vm_start);
+        if (pol) {
+                mpol_to_str(buffer, sizeof(buffer), pol);
+                mpol_cond_put(pol);
+        } else {
+                mpol_to_str(buffer, sizeof(buffer), proc_priv->task_mempolicy);
+        }
 
         seq_printf(m, "%08lx %s", vma->vm_start, buffer);