linux-kernel - Re: kfree(0)

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Message-ID: <Pine.LNX.4.64.0708171621260.12644@schroedinger.engr.sgi.com>
Date:	Fri, 17 Aug 2007 16:22:09 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Pekka Enberg <penberg@...helsinki.fi>
cc:	Satyam Sharma <satyam@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Tim Bird <tim.bird@...sony.com>,
	linux kernel <linux-kernel@...r.kernel.org>
Subject: Re: kfree(0) - ok?

On Sat, 18 Aug 2007, Pekka Enberg wrote:

> Agreed, especially as we have real zero-sized objects returned from
> kmalloc() et al now.



Slab allocators: Fail if ksize is called with a NULL parameter

A NULL pointer means that the object was not allocated. One cannot
determine the size of an object that has not been allocated. Currently
we return 0 but we really should BUG() on attempts to determine the size
of something nonexistent.

krealloc() interprets NULL to mean a zero sized object. Handle that
separately in krealloc().

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

Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c	2007-08-17 16:17:41.000000000 -0700
+++ linux-2.6/mm/slab.c	2007-08-17 16:18:15.000000000 -0700
@@ -4436,7 +4436,8 @@ const struct seq_operations slabstats_op
  */
 size_t ksize(const void *objp)
 {
-	if (unlikely(ZERO_OR_NULL_PTR(objp)))
+	BUG_ON(!objp);
+	if (unlikely(objp == ZERO_SIZE_PTR))
 		return 0;
 
 	return obj_size(virt_to_cache(objp));
Index: linux-2.6/mm/slob.c
===================================================================
--- linux-2.6.orig/mm/slob.c	2007-08-17 16:18:19.000000000 -0700
+++ linux-2.6/mm/slob.c	2007-08-17 16:18:40.000000000 -0700
@@ -484,7 +484,8 @@ size_t ksize(const void *block)
 {
 	struct slob_page *sp;
 
-	if (ZERO_OR_NULL_PTR(block))
+	BUG_ON(!block);
+	if (block == ZERO_SIZE_PTR)
 		return 0;
 
 	sp = (struct slob_page *)virt_to_page(block);
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2007-08-17 16:16:36.000000000 -0700
+++ linux-2.6/mm/slub.c	2007-08-17 16:17:36.000000000 -0700
@@ -2426,7 +2426,8 @@ size_t ksize(const void *object)
 	struct page *page;
 	struct kmem_cache *s;
 
-	if (ZERO_OR_NULL_PTR(object))
+	BUG_ON(!object);
+	if (object == ZERO_SIZE_PTR)
 		return 0;
 
 	page = get_object_page(object);
Index: linux-2.6/mm/util.c
===================================================================
--- linux-2.6.orig/mm/util.c	2007-08-17 16:16:29.000000000 -0700
+++ linux-2.6/mm/util.c	2007-08-17 16:16:32.000000000 -0700
@@ -81,14 +81,16 @@ EXPORT_SYMBOL(kmemdup);
 void *krealloc(const void *p, size_t new_size, gfp_t flags)
 {
 	void *ret;
-	size_t ks;
+	size_t ks = 0;
 
 	if (unlikely(!new_size)) {
 		kfree(p);
 		return ZERO_SIZE_PTR;
 	}
 
-	ks = ksize(p);
+	if (p)
+		ks = ksize(p);
+
 	if (ks >= new_size)
 		return (void *)p;
 
 
-
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