lkml.org 
[lkml]   [2015]   [May]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC] rmap: fix "race" between do_wp_page and shrink_active_list
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.

Thanks,
Vladimir


\
 
 \ /
  Last update: 2015-05-12 10:41    [W:0.391 / U:0.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site