memcg: make page->mapping NULL before uncharge

This patch tries to make page->mapping to be NULL before
mem_cgroup_uncharge_cache_page() is called.

"page->mapping == NULL" is a good check for "whether the page is still
radix-tree or not".  This patch also adds BUG_ON() to
mem_cgroup_uncharge_cache_page();

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index e1b23fda48de..ab8553658af3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -116,12 +116,12 @@ void __remove_from_page_cache(struct page *page)
 {
         struct address_space *mapping = page->mapping;
 
-        mem_cgroup_uncharge_cache_page(page);
         radix_tree_delete(&mapping->page_tree, page->index);
         page->mapping = NULL;
         mapping->nrpages--;
         __dec_zone_page_state(page, NR_FILE_PAGES);
         BUG_ON(page_mapped(page));
+        mem_cgroup_uncharge_cache_page(page);
 
         /*
          * Some filesystems seem to re-dirty the page even after