Re: Oops in a driver while using SLUB as a SLAB allocator

[Hugh Dickins <hugh@veritas.com>]

On Thu, 21 Jun 2007, Christoph Lameter wrote:

> Maybe this will address the issue on ARM?

Looks like it would indeed address the immediate issue on ARM -
IF they've no particular reason to be using kmalloc there.

However... what gives you confidence that flush_dcache_page is
never applied to other slab pages?

This looks to me like a clean way forward to try in -mm; but that
2.6.22 should go with the safety PageSlab test in page_mapping.

Hugh

> 
> 
> ARM: Allocate dma pages via the page allocator and not via the slab allocator
> 
> Slab allocations are not guaranteed to be page aligned and slab allocators
> may use the page structs for their own purposes. Using the page allocator
> yields a properly aligned page and also makes the page flushing logic work right.
> 
> Passing a kmalloced "page" to a flushing function will not work reliably.
> 
> This will hopefully address the issue with SLUB on ARM. SLUB uses the
> page->mapping field which is also checked by the flushing logic. The
> flushing logic expects a normal page and not a slab page.
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> ---
>  arch/arm/mm/consistent.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/arch/arm/mm/consistent.c
> ===================================================================
> --- linux-2.6.orig/arch/arm/mm/consistent.c	2007-06-21 18:18:15.000000000 -0700
> +++ linux-2.6/arch/arm/mm/consistent.c	2007-06-21 18:29:16.000000000 -0700
> @@ -277,7 +277,7 @@ dma_alloc_coherent(struct device *dev, s
>  	if (arch_is_coherent()) {
>  		void *virt;
>  
> -		virt = kmalloc(size, gfp);
> +		virt = get_free_pages(gfp, get_order(size));
>  		if (!virt)
>  			return NULL;
>  		*handle =  virt_to_dma(dev, virt);
> @@ -364,7 +364,7 @@ void dma_free_coherent(struct device *de
>  	WARN_ON(irqs_disabled());
>  
>  	if (arch_is_coherent()) {
> -		kfree(cpu_addr);
> +		free_pages((unsigned long)cpu_addr, get_order(size));
>  		return;
>  	}
>  
>