linux-kernel - [PATCH 3/4] mempolicy: sanitize the usage of get_task

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Date:	Wed, 20 Aug 2014 21:23:30 +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 3/4] mempolicy: sanitize the usage of get_task_policy()

Cleanup + preparation. Every user of get_task_policy() calls it
unconditionally, even if it is not going to use the result.

get_task_policy() is cheap but still this does not look clean, plus
the code looks simpler if get_task_policy() is called only when this
is really needed.

Note: I hope this is correct, but it is not clear why vma_policy_mof()
doesn't fall back to get_task_policy() if ->get_policy() returns NULL.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 mm/mempolicy.c |   25 ++++++++++++++-----------
 1 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 656db97..b86b08e 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1621,14 +1621,11 @@ COMPAT_SYSCALL_DEFINE6(mbind, compat_ulong_t, start, compat_ulong_t, len,
 struct mempolicy *get_vma_policy(struct task_struct *task,
 		struct vm_area_struct *vma, unsigned long addr)
 {
-	struct mempolicy *pol = get_task_policy(task);
+	struct mempolicy *pol = NULL;
 
 	if (vma) {
 		if (vma->vm_ops && vma->vm_ops->get_policy) {
-			struct mempolicy *vpol = vma->vm_ops->get_policy(vma,
-									addr);
-			if (vpol)
-				pol = vpol;
+			pol = vma->vm_ops->get_policy(vma, addr);
 		} else if (vma->vm_policy) {
 			pol = vma->vm_policy;
 
@@ -1643,12 +1640,15 @@ struct mempolicy *get_vma_policy(struct task_struct *task,
 		}
 	}
 
+	if (!pol)
+		pol = get_task_policy(task);
+
 	return pol;
 }
 
 bool vma_policy_mof(struct task_struct *task, struct vm_area_struct *vma)
 {
-	struct mempolicy *pol = get_task_policy(task);
+	struct mempolicy *pol = NULL;
 
 	if (vma) {
 		if (vma->vm_ops && vma->vm_ops->get_policy) {
@@ -1660,11 +1660,14 @@ bool vma_policy_mof(struct task_struct *task, struct vm_area_struct *vma)
 			mpol_cond_put(pol);
 
 			return ret;
-		} else if (vma->vm_policy) {
-			pol = vma->vm_policy;
 		}
+
+		pol = vma->vm_policy;
 	}
 
+	if (!pol)
+		pol = get_task_policy(task);
+
 	return pol->flags & MPOL_F_MOF;
 }
 
@@ -2068,12 +2071,12 @@ retry_cpuset:
  */
 struct page *alloc_pages_current(gfp_t gfp, unsigned order)
 {
-	struct mempolicy *pol = get_task_policy(current);
+	struct mempolicy *pol = &default_policy;
 	struct page *page;
 	unsigned int cpuset_mems_cookie;
 
-	if (in_interrupt() || (gfp & __GFP_THISNODE))
-		pol = &default_policy;
+	if (!in_interrupt() && !(gfp & __GFP_THISNODE))
+		pol = get_task_policy(current);
 
 retry_cpuset:
 	cpuset_mems_cookie = read_mems_allowed_begin();
-- 
1.5.5.1


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