mempolicy: remove the "task" arg of vma_policy_mof() and simplify it

1. vma_policy_mof(task) is simply not safe unless task == current,
   it can race with do_exit()->mpol_put(). Remove this arg and update
   its single caller.

2. vma can not be NULL, remove this check and simplify the code.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 13 insertions, 16 deletions

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index f230a978e6ba..5e4bfcedd2ce 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -136,7 +136,7 @@ struct mempolicy *mpol_shared_policy_lookup(struct shared_policy *sp,
 
 struct mempolicy *get_vma_policy(struct task_struct *tsk,
                 struct vm_area_struct *vma, unsigned long addr);
-bool vma_policy_mof(struct task_struct *task, struct vm_area_struct *vma);
+bool vma_policy_mof(struct vm_area_struct *vma);
 
 extern void numa_default_policy(void);
 extern void numa_policy_init(void);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bfa3c86d0d68..82088b29704e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1946,7 +1946,7 @@ void task_numa_work(struct callback_head *work)
                 vma = mm->mmap;
         }
         for (; vma; vma = vma->vm_next) {
-                if (!vma_migratable(vma) || !vma_policy_mof(p, vma))
+                if (!vma_migratable(vma) || !vma_policy_mof(vma))
                         continue;
 
                 /*
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b86b08e77b8d..ad27bbc757bf 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1646,27 +1646,24 @@ struct mempolicy *get_vma_policy(struct task_struct *task,
         return pol;
 }
 
-bool vma_policy_mof(struct task_struct *task, struct vm_area_struct *vma)
+bool vma_policy_mof(struct vm_area_struct *vma)
 {
-        struct mempolicy *pol = NULL;
-
-        if (vma) {
-                if (vma->vm_ops && vma->vm_ops->get_policy) {
-                        bool ret = false;
+        struct mempolicy *pol;
 
-                        pol = vma->vm_ops->get_policy(vma, vma->vm_start);
-                        if (pol && (pol->flags & MPOL_F_MOF))
-                                ret = true;
-                        mpol_cond_put(pol);
+        if (vma->vm_ops && vma->vm_ops->get_policy) {
+                bool ret = false;
 
-                        return ret;
-                }
+                pol = vma->vm_ops->get_policy(vma, vma->vm_start);
+                if (pol && (pol->flags & MPOL_F_MOF))
+                        ret = true;
+                mpol_cond_put(pol);
 
-                pol = vma->vm_policy;
+                return ret;
         }
 
+        pol = vma->vm_policy;
         if (!pol)
-                pol = get_task_policy(task);
+                pol = get_task_policy(current);
 
         return pol->flags & MPOL_F_MOF;
 }