memcg: fix ugly initialization of return value is in caller

Remove initialization of vaiable in caller of memory cgroup function.
Actually, it's return value of memcg function but it's initialized in
caller.

Some memory cgroup uses following style to bring the result of start
function to the end function for avoiding races.

   mem_cgroup_start_A(&(*ptr))
   /* Something very complicated can happen here. */
   mem_cgroup_end_A(*ptr)

In some calls, *ptr should be initialized to NULL be caller.  But it's
ugly.  This patch fixes that *ptr is initialized by _start function.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-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/memory.c b/mm/memory.c
index 615be5127ce1..20d5f7499ce2 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2767,7 +2767,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         swp_entry_t entry;
         pte_t pte;
         int locked;
-        struct mem_cgroup *ptr = NULL;
+        struct mem_cgroup *ptr;
         int exclusive = 0;
         int ret = 0;