On Mon, May 04, 2015 at 07:54:59PM +0900, Minchan Kim wrote: > So, I guess once below compiler optimization happens in __page_set_anon_rmap, > it could be corrupt in page_refernced. > > __page_set_anon_rmap: > page->mapping = (struct address_space *) anon_vma; > page->mapping = (struct address_space *)((void *)page_mapping + PAGE_MAPPING_ANON); > > Because page_referenced checks it with PageAnon which has no memory barrier. > So if above compiler optimization happens, page_referenced can pass the anon > page in rmap_walk_file, not ramp_walk_anon. It's my theory. :) FWIW If such splits were possible, we would have bugs all over the kernel IMO. An example is do_wp_page() vs shrink_active_list(). In do_wp_page() we can call page_move_anon_rmap(), which sets page->mapping in exactly the same fashion as above-mentioned __page_set_anon_rmap(): anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; page->mapping = (struct address_space *) anon_vma; The page in question may be on an LRU list, because nowhere in do_wp_page() we remove it from the list, neither do we take any LRU related locks. The page is locked, that's true, but shrink_active_list() calls page_referenced() on an unlocked page, so according to your logic they can race with the latter receiving a page with page->mapping equal to anon_vma w/o PAGE_MAPPING_ANON bit set: 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+PAGE_MAPPING_ANON However, this does not happen. Thanks, Vladimir -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
