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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