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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