Re: [RFC][PATCH v1 11/11] mm: hwpoison: introduce clear_hwpoison_free_buddy_page()

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

On Fri, Nov 09, 2018 at 05:03:06PM +0530, Anshuman Khandual wrote:
> 
> 
> On 11/09/2018 12:17 PM, Naoya Horiguchi wrote:
> > The new function is a reverse operation of set_hwpoison_free_buddy_page()
> > to adjust unpoison_memory() to the new semantics.
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> 
> snip
> 
> > +
> > +/*
> > + * Reverse operation of set_hwpoison_free_buddy_page(), which is expected
> > + * to work only on error pages isolated from buddy allocator.
> > + */
> > +bool clear_hwpoison_free_buddy_page(struct page *page)
> > +{
> > +	struct zone *zone = page_zone(page);
> > +	bool unpoisoned = false;
> > +
> > +	spin_lock(&zone->lock);
> > +	if (TestClearPageHWPoison(page)) {
> > +		unsigned long pfn = page_to_pfn(page);
> > +		int migratetype = get_pfnblock_migratetype(page, pfn);
> > +
> > +		__free_one_page(page, pfn, zone, 0, migratetype);
> > +		unpoisoned = true;
> > +	}
> > +	spin_unlock(&zone->lock);
> > +	return unpoisoned;
> > +}
> >  #endif
> > 
> 
> Though there are multiple page state checks in unpoison_memory() leading
> upto clearing HWPoison flag, the page must not be in buddy already if
> __free_one_page() would be called on it.

Yes, you're right.
clear_hwpoison_free_buddy_page() is intended to cancel the isolation by
set_hwpoison_free_buddy_page() which removes the target page from buddy allocator,
so the page clear_hwpoison_free_buddy_page() tries to handle is not a buddy page
actually (not linked to any freelist).

Thanks,
Naoya Horiguchi