Re: [PATCH v2] mm: don't expose page to fast gup prematurely

[Kirill A. Shutemov]

On Sat, Sep 14, 2019 at 01:05:18AM -0600, Yu Zhao wrote:
> We don't want to expose page to fast gup running on a remote CPU
> before all local non-atomic ops on page flags are visible first.
> 
> For anon page that isn't in swap cache, we need to make sure all
> prior non-atomic ops, especially __SetPageSwapBacked() in
> page_add_new_anon_rmap(), are order before set_pte_at() to prevent
> the following race:
> 
> 	CPU 1				CPU1
> set_pte_at()			get_user_pages_fast()
> page_add_new_anon_rmap()		gup_pte_range()
> 	__SetPageSwapBacked()			SetPageReferenced()

Is there a particular codepath that has what you listed for CPU?
After quick look, I only saw that we page_add_new_anon_rmap() called
before set_pte_at().

-- 
 Kirill A. Shutemov