On Thu, Apr 08, 2021 at 03:04:20PM +0100, David Howells wrote:
> +static inline void set_page_private_2(struct page *page)
> +{
> + get_page(page);
> + SetPagePrivate2(page);
PAGEFLAG(OwnerPriv1, owner_priv_1, PF_ANY)
So we can set Private2 on any tail page ...
> +void end_page_private_2(struct page *page)
> +{
> + page = compound_head(page);
> + VM_BUG_ON_PAGE(!PagePrivate2(page), page);
> + clear_bit_unlock(PG_private_2, &page->flags);
> + wake_up_page_bit(page, PG_private_2);
... but when we try to end on a tail, we actually wake up the head ...
> +void wait_on_page_private_2(struct page *page)
> +{
> + while (PagePrivate2(page))
> + wait_on_page_bit(page, PG_private_2);
... although if we were waiting on a tail, the wake up won't find us ...
if only we had a way to ensure this kind of bug can't happen *cough,
lend your support to the page folio patches*.
