On Saturday, 11 December 2021 3:34:36 PM AEDT Matthew Wilcox wrote: > On Thu, Nov 18, 2021 at 01:54:27PM -0800, akpm@xxxxxxxxxxxxxxxxxxxx wrote: > > +++ a/mm/migrate.c > > @@ -305,15 +305,7 @@ void __migration_entry_wait(struct mm_st > > page = pfn_swap_entry_to_page(entry); > > page = compound_head(page); > > > > - /* > > - * Once page cache replacement of page migration started, page_count > > - * is zero; but we must not call put_and_wait_on_page_locked() without > > - * a ref. Use get_page_unless_zero(), and just fault again if it fails. > > - */ > > - if (!get_page_unless_zero(page)) > > - goto out; > > - pte_unmap_unlock(ptep, ptl); > > - put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE); > > + migration_entry_wait_on_locked(page_folio(page), ptep, ptl); > > This is clearly bogus. The 'page = compound_head(page)' line should > be deleted. > > But I think we should go further and turn this into: > > migration_entry_wait_on_locked(entry, ptep, ptl); > > Neither caller has anything useful to do with the page any more. Thanks for spotting that, I have posted a new version which does that.
