linux-kernel - Re: mm: slub: invalid memory access in setup

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Date:	Tue, 1 Jul 2014 09:58:52 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	David Rientjes <rientjes@...gle.com>
cc:	Sasha Levin <sasha.levin@...cle.com>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: mm: slub: invalid memory access in setup_object

On Mon, 30 Jun 2014, David Rientjes wrote:

> It's not at all clear to me that that patch is correct.  Wei?

Looks ok to me. But I do not like the convoluted code in new_slab() which
Wei's patch does not make easier to read. Makes it difficult for the
reader to see whats going on.

Lets drop the use of the variable named "last".


Subject: slub: Only call setup_object once for each object

Modify the logic for object initialization to be less convoluted
and initialize an object only once.

Signed-off-by: Christoph Lameter <cl@...ux.com>

Index: linux/mm/slub.c
===================================================================
--- linux.orig/mm/slub.c	2014-07-01 09:50:02.486846653 -0500
+++ linux/mm/slub.c	2014-07-01 09:52:07.918802585 -0500
@@ -1409,7 +1409,6 @@ static struct page *new_slab(struct kmem
 {
 	struct page *page;
 	void *start;
-	void *last;
 	void *p;
 	int order;

@@ -1432,15 +1431,11 @@ static struct page *new_slab(struct kmem
 	if (unlikely(s->flags & SLAB_POISON))
 		memset(start, POISON_INUSE, PAGE_SIZE << order);

-	last = start;
 	for_each_object(p, s, start, page->objects) {
-		setup_object(s, page, last);
-		set_freepointer(s, last, p);
-		last = p;
+		setup_object(s, page, p);
+		set_freepointer(s, p, p + s->size);
 	}
-	setup_object(s, page, last);
-	set_freepointer(s, last, NULL);
-
+	set_freepointer(s, start + (page->objects - 1) * s->size, NULL);
 	page->freelist = start;
 	page->inuse = page->objects;
 	page->frozen = 1;
--
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