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

yalin
2015-05-17T12:48:31Z

> 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!