Re: [RFC] rmap: fix "race" between do_wp_page and shrink_active_list

[yalin]

> On Mon, May 11, 2015 at 04:59:27PM +0800, yalin wang wrote:
> > i am confused about your analysis ,
> > for the race stack:
> >
> > CPU0                          CPU1
> >
> >     ----                          ----
> >
> >     do_wp_page                    shrink_active_list
> >
> >      lock_page                     page_referenced
> >
> >                                     PageAnon->yes, so skip trylock_page
> >
> >      page_move_anon_rmap
> >
> >       page->mapping = anon_vma
> >
> >                                     rmap_walk
> >
> >                                      PageAnon->no
> >
> >                                      rmap_walk_file
> >
> >                                       BUG
> >
> >       page->mapping += PAGE_MAPPING_ANON
> >
> > the page should must change from PageAnon() to !PageAnon() when crash happened.
> > but page_move_anon_rmap() is doing change a page from !PageAnon()
> > (swapcache page) to PageAnon() ,
> A swapcache page is not necessarily !PageAnon. In do_wp_page() old_page
> *is* PageAnon. It may or may not be on the swapcache though, which does
> not really matter.
>
> > how does this race condition crash happened ?
> It never happened. It might theoretically happen due to a compiler
> "optimization" I described above.
i see,
Thanks for your explanation!

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