commit 56039efa18f2530fc23e8ef19e716b65ee2a1d1e
author KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Wed Mar 23 16:42:19 2011 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Wed Mar 23 19:46:22 2011 -0700
tree a61cbd2f760e93363657622de2cd1591db028458
parent 6c191cd01a935e5b53ef43c9403c771bb7a32b60

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>

mm/memcontrol.c

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e1ee6ad..b56bd74 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2475,7 +2475,7 @@
 
 	/* shmem */
 	if (PageSwapCache(page)) {
-		struct mem_cgroup *mem = NULL;
+		struct mem_cgroup *mem;
 
 		ret = mem_cgroup_try_charge_swapin(mm, page, gfp_mask, &mem);
 		if (!ret)
@@ -2501,6 +2501,8 @@
 	struct mem_cgroup *mem;
 	int ret;
 
+	*ptr = NULL;
+
 	if (mem_cgroup_disabled())
 		return 0;
 
@@ -2916,6 +2918,8 @@
 	enum charge_type ctype;
 	int ret = 0;
 
+	*ptr = NULL;
+
 	VM_BUG_ON(PageTransHuge(page));
 	if (mem_cgroup_disabled())
 		return 0;
@@ -3058,7 +3062,7 @@
 			    struct mm_struct *mm,
 			    gfp_t gfp_mask)
 {
-	struct mem_cgroup *mem = NULL;
+	struct mem_cgroup *mem;
 	int ret;
 
 	if (mem_cgroup_disabled())

mm/memory.c

diff --git a/mm/memory.c b/mm/memory.c
index 615be51..20d5f74 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2767,7 +2767,7 @@
 	swp_entry_t entry;
 	pte_t pte;
 	int locked;
-	struct mem_cgroup *ptr = NULL;
+	struct mem_cgroup *ptr;
 	int exclusive = 0;
 	int ret = 0;
 

mm/migrate.c

diff --git a/mm/migrate.c b/mm/migrate.c
index 89e5c3f..b0406d7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -633,7 +633,7 @@
 	struct page *newpage = get_new_page(page, private, &result);
 	int remap_swapcache = 1;
 	int charge = 0;
-	struct mem_cgroup *mem = NULL;
+	struct mem_cgroup *mem;
 	struct anon_vma *anon_vma = NULL;
 
 	if (!newpage)

mm/swapfile.c

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 71b42ec..039e616 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -880,7 +880,7 @@
 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		unsigned long addr, swp_entry_t entry, struct page *page)
 {
-	struct mem_cgroup *ptr = NULL;
+	struct mem_cgroup *ptr;
 	spinlock_t *ptl;
 	pte_t *pte;
 	int ret = 1;