Re: [RFC] rmap: fix "race" between do_wp_page and shrink_active_list
From: Vladimir Davydov
Date: Tue May 12 2015 - 04:35:09 EST
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->mapping = anon_vma
> 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.
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