memcg: move charge swapin under lock

While page-cache's charge/uncharge is done under page_lock(), swap-cache
isn't.  (anonymous page is charged when it's newly allocated.)

This patch moves do_swap_page()'s charge() call under lock.  I don't see
any bad problem *now* but this fix will be good for future for avoiding
unnecessary racy state.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: 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, 6 insertions, 5 deletions

diff --git a/mm/memory.c b/mm/memory.c
index ba86b436b85f..54cf20ee0a83 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2326,16 +2326,17 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 count_vm_event(PGMAJFAULT);
         }
 
+        mark_page_accessed(page);
+
+        lock_page(page);
+        delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+
         if (mem_cgroup_charge(page, mm, GFP_KERNEL)) {
-                delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
                 ret = VM_FAULT_OOM;
+                unlock_page(page);
                 goto out;
         }
 
-        mark_page_accessed(page);
-        lock_page(page);
-        delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
-
         /*
          * Back out if somebody else already faulted in this pte.
          */