[RFC/PATCH 2/7] ARM: ARM11 MPCore: pte_alloc_one{,_kernel} are not preempt safe

[Russell King - ARM Linux]

On Thu, Oct 06, 2011 at 10:38:36PM -0400, gdavis at mvista.com wrote:
> -#define PGALLOC_GFP	(GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT | __GFP_ZERO)
> +#define PGALLOC_GFP	(GFP_KERNEL | __GFP_NOTRACK | __GFP_REPEAT)
> @@ -81,8 +88,14 @@ pte_alloc_one(struct mm_struct *mm, unsigned long addr)
>  	pte = alloc_pages(PGALLOC_GFP, 0);
>  #endif
>  	if (pte) {
> +		void *p = page_address(pte);
> +		if (cache_ops_need_broadcast())
> +			preempt_disable();
> +		memset(p, 0, PAGE_SIZE);
>  		if (!PageHighMem(pte))
> -			clean_pte_table(page_address(pte));
> +			clean_pte_table(p);
> +		if (cache_ops_need_broadcast())
> +			preempt_enable();

This won't work - page_address(pte) will be NULL for highmem pages, and
so will cause an oops, and removing the __GFP_ZERO will mean that highmem
pages will not be zeroed, meaning that such page tables will not have been
initialized.