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SubjectRe: [PATCH v27 3/4] mm/page_poison: expose page_poisoning_enabled to kernel modules
On 02/08/2018 02:34 AM, Michael S. Tsirkin wrote:
> On Wed, Feb 07, 2018 at 02:54:30PM +0800, Wei Wang wrote:
>> In some usages, e.g. virtio-balloon, a kernel module needs to know if
>> page poisoning is in use. This patch exposes the page_poisoning_enabled
>> function to kernel modules.
>>
>> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Michal Hocko <mhocko@kernel.org>
>> Cc: Michael S. Tsirkin <mst@redhat.com>
>> ---
>> mm/page_poison.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/mm/page_poison.c b/mm/page_poison.c
>> index e83fd44..c08d02a 100644
>> --- a/mm/page_poison.c
>> +++ b/mm/page_poison.c
>> @@ -30,6 +30,11 @@ bool page_poisoning_enabled(void)
>> debug_pagealloc_enabled()));
>> }
>>
>> +/**
>> + * page_poisoning_enabled - check if page poisoning is enabled
>> + *
>> + * Return true if page poisoning is enabled, or false if not.
>> + */
>> static void poison_page(struct page *page)
>> {
>> void *addr = kmap_atomic(page);
>> @@ -37,6 +42,7 @@ static void poison_page(struct page *page)
>> memset(addr, PAGE_POISON, PAGE_SIZE);
>> kunmap_atomic(addr);
>> }
>> +EXPORT_SYMBOL_GPL(page_poisoning_enabled);
>>
>> static void poison_pages(struct page *page, int n)
>> {
> Looks like both the comment and the export are in the wrong place.

Thanks. Will be more careful.

> I'm a bit concerned that callers also in fact poke at the
> PAGE_POISON - exporting that seems to be more of an accident
> as it's only used without page_poisoning.c - it might be
> better to have page_poisoning_enabled get u8 * and set it.
>

PAGE_POISON is a macro defined in the header, why would callers using it
be a concern?

Do you suggest to have:

bool page_poisoning_get(u8 *val)
{
if (page_poisoning_enabled()) {
*val = PAGE_POISON;
return true;
}

return false;
}
EXPORT_SYMBOL_GPL(page_poisoning_get);


Best,
Wei

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