linux-kernel - Re: Uninline kcalloc

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Date:	Tue, 14 Feb 2012 13:37:44 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Xi Wang <xi.wang@...il.com>
cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesper Juhl <jj@...osbits.net>, Jens Axboe <axboe@...nel.dk>,
	Pekka Enberg <penberg@...nel.org>,
	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: Uninline kcalloc

This patch still preserves kcalloc. But note that if kcalloc returns NULL
then multiple conditions may have caused it. One is that the array is
simply too large. The other may be that such an allocation is not possible
due to fragmentation.


Subject: Introduce calculate_array_size

calculate_array_size calculates the size of an array while
checking for errors. Returns 0 if the size is too large.

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


---
 include/linux/slab.h |   15 +++++++++++++++
 mm/util.c            |    9 ++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

Index: linux-2.6/include/linux/slab.h
===================================================================
--- linux-2.6.orig/include/linux/slab.h	2012-02-14 13:32:43.000000000 -0600
+++ linux-2.6/include/linux/slab.h	2012-02-14 13:34:41.000000000 -0600
@@ -242,6 +242,21 @@ size_t ksize(const void *);
  */
 void *kcalloc(size_t n, size_t size, gfp_t flags);

+/*
+ * calculate_array_size - Calculate an array size given the size of a
+ * particular element with checking for overflow.
+ *
+ * Return 0 if there is an overflow.
+ */
+static inline long calculate_array_size(size_t n, size_t size)
+{
+	if (size != 0 && n > ULONG_MAX / size)
+
+		return 0;
+
+	return n * size;
+}
+
 #if !defined(CONFIG_NUMA) && !defined(CONFIG_SLOB)
 /**
  * kmalloc_node - allocate memory from a specific node
Index: linux-2.6/mm/util.c
===================================================================
--- linux-2.6.orig/mm/util.c	2012-02-14 13:32:54.000000000 -0600
+++ linux-2.6/mm/util.c	2012-02-14 13:34:10.000000000 -0600
@@ -83,9 +83,12 @@ EXPORT_SYMBOL(kmemdup);
  */
 void *kcalloc(size_t n, size_t size, gfp_t flags)
 {
-	if (size != 0 && n > ULONG_MAX / size)
-		return NULL;
-	return __kmalloc(n * size, flags | __GFP_ZERO);
+	size_t s = calculate_array_size(n, size);
+
+	if (s)
+		return kzalloc(s, flags);
+
+	return NULL;
 }
 EXPORT_SYMBOL(kcalloc);

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