[PATCH] __kmalloc: Generate BUG if size requested is too large.

[PATCH] __kmalloc: Generate BUG if size requested is too large.

[Christoph Lameter]

I had an issue on ia64 where I got a bug in kernel/workqueue because kzalloc
returned a NULL pointer due to the task structure getting too big for the slab
allocator. Usually these cases are caught by the kmalloc macro in include/linux/slab.h.
Compilation will fail if a too big value is passed to kmalloc.

However, kzalloc uses __kmalloc which has no check for that. This patch makes __kmalloc
bug if a too large entity is requested.

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

Index: linux-2.6.14-rc2/mm/slab.c
===================================================================
--- linux-2.6.14-rc2.orig/mm/slab.c	2005-09-22 11:21:07.000000000 -0700
+++ linux-2.6.14-rc2/mm/slab.c	2005-09-22 11:58:45.000000000 -0700
@@ -2906,8 +2906,7 @@ void *__kmalloc(size_t size, unsigned in
 	 * functions.
 	 */
 	cachep = __find_general_cachep(size, flags);
-	if (unlikely(cachep == NULL))
-		return NULL;
+	BUG_ON(!cachep);		/* Allocation size too large for kmalloc */
 	return __cache_alloc(cachep, flags);
 }
 EXPORT_SYMBOL(__kmalloc);

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Re: [PATCH] __kmalloc: Generate BUG if size requested is too large.

[Dave Hansen]

On Thu, 2005-09-22 at 12:32 -0700, Christoph Lameter wrote:
> I had an issue on ia64 where I got a bug in kernel/workqueue because kzalloc
> returned a NULL pointer due to the task structure getting too big for the slab
> allocator. Usually these cases are caught by the kmalloc macro in include/linux/slab.h.
> Compilation will fail if a too big value is passed to kmalloc.

I'd be more concerned that the workqueue code wasn't checking for NULL.
Also, the one place where I see the workqueue code using kzalloc(), it
checks for kzalloc() failure (in __create_workqueue).

> However, kzalloc uses __kmalloc which has no check for that. This
> patch makes __kmalloc bug if a too large entity is requested.

I don't see that in current -git, either.  Which version of the kernel
are you working against?

> void *kzalloc(size_t size, unsigned int __nocast flags)
> {
>         void *ret = kmalloc(size, flags);
>         if (ret)
>                 memset(ret, 0, size);
>         return ret;
> }
> EXPORT_SYMBOL(kzalloc);

-- Dave

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Re: [PATCH] __kmalloc: Generate BUG if size requested is too large.

[Christoph Lameter]

On Thu, 22 Sep 2005, Dave Hansen wrote:

> On Thu, 2005-09-22 at 12:32 -0700, Christoph Lameter wrote:
> > I had an issue on ia64 where I got a bug in kernel/workqueue because kzalloc
> > returned a NULL pointer due to the task structure getting too big for the slab
> > allocator. Usually these cases are caught by the kmalloc macro in include/linux/slab.h.
> > Compilation will fail if a too big value is passed to kmalloc.
> 
> I'd be more concerned that the workqueue code wasn't checking for NULL.
> Also, the one place where I see the workqueue code using kzalloc(), it
> checks for kzalloc() failure (in __create_workqueue).

The workqueue code is checking for NULL after getting out of a another 
function. 

> > However, kzalloc uses __kmalloc which has no check for that. This
> > patch makes __kmalloc bug if a too large entity is requested.
> 
> I don't see that in current -git, either.  Which version of the kernel
> are you working against?

Look at __kmalloc in current not kzalloc. kzalloc calls __kmalloc 
since size is not a constant.

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