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

[George G. Davis]

On Oct 7, 2011, at 3:47 AM, Russell King - ARM Linux wrote:

> 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.

Yep, I had a feeling that it was not going to work correctly for the HIGHMEM case.
Alas, I'm not using HIGHMEM so I did not see the issue in my testing.  I'll respin it to fix
HIGHMEM breakage.

Thanks!

--
Regards,
George