linux-kernel - [ 89/89] slub: assign refcount for kmalloc

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Date:	Fri,  1 Feb 2013 14:08:44 +0100
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Paul Hargrove <phhargrove@....gov>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <js1304@...il.com>, CAI Qian <caiqian@...hat.com>
Subject: [ 89/89] slub: assign refcount for kmalloc_caches

3.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: CAI Qian <caiqian@...hat.com>

This is for stable-3.7.y only and this problem has already been solved
in mainline through some slab/slub re-work which isn't suitable to
backport here. See create_kmalloc_cache() in mm/slab_common.c there.

commit cce89f4f6911286500cf7be0363f46c9b0a12ce0('Move kmem_cache
refcounting to common code') moves some refcount manipulation code to
common code. Unfortunately, it also removed refcount assignment for
kmalloc_caches. So, kmalloc_caches's refcount is initially 0.
This makes erroneous situation.

Paul Hargrove report that when he create a 8-byte kmem_cache and
destory it, he encounter below message.
'Objects remaining in kmalloc-8 on kmem_cache_close()'

8-byte kmem_cache merge with 8-byte kmalloc cache and refcount is
increased by one. So, resulting refcount is 1. When destroy it, it hit
refcount = 0, then kmem_cache_close() is executed and error message is
printed.

This patch assign initial refcount 1 to kmalloc_caches, so fix this
erroneous situation.

Reported-by: Paul Hargrove <phhargrove@....gov>
Cc: Christoph Lameter <cl@...ux.com>
Signed-off-by: Joonsoo Kim <js1304@...il.com>
Signed-off-by: CAI Qian <caiqian@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/slub.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3279,6 +3279,7 @@ static struct kmem_cache *__init create_
 	if (kmem_cache_open(s, flags))
 		goto panic;

+	s->refcount = 1;
 	list_add(&s->list, &slab_caches);
 	return s;

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