linux-kernel - [PATCH 4/4] mempolicy: remove the "task" arg of vma_policy

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Date:	Wed, 20 Aug 2014 21:23:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 4/4] 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@...hat.com>
---
 include/linux/mempolicy.h |    2 +-
 kernel/sched/fair.c       |    2 +-
 mm/mempolicy.c            |   25 +++++++++++--------------
 3 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index f230a97..5e4bfce 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 bfa3c86..82088b2 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 b86b08e..ad27bbc 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;
 }
-- 
1.5.5.1


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