Re: [PATCH v8 10/15] mm: Check individual hugetlb pages for poison

On Fri, Jul 31, 2026 at 09:07:55PM +0100, Matthew Wilcox (Oracle) wrote:
> +/*
> + * We have no reference on the folio containing this page.
> + * The hugetlb_lock keeps hugetlb folios from being freed.
> + */
> +bool hugetlb_unref_page_hwpoison(const struct page *page)
> +{
> +	const struct folio *folio;
> +	unsigned long flags;
> +	bool ret;
> +
> +	spin_lock_irqsave(&hugetlb_lock, flags);
> +	folio = page_folio(page);
> +	if (!folio_test_huge_poison(folio)) {
> +		ret = PageHWPoison(page);
> +		goto unlock;
> +	}
> +
> +	ret = precise_page_poisoned(folio, page);
> +unlock:
> +	spin_unlock_irqrestore(&hugetlb_lock, flags);
> +	return ret;
> +}
> +

I ended up with the same question as sashiko - i think this behavior
implies we must hold a reference on the page, otherwise the folio can
be invalid and all these accesses are unsafe.

But that must be the existing behavior for poison checks like this, so
this is at least no worse. Not sure it's worth addressing.

Reviewed-by: Gregory Price (Meta) <[email protected]>