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>

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e1ee6ad9c9718c4bd973cc2dd3b92085e410345c..b56bd74b486fb539e6e893151b0e0af42395444a 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2475,7 +2475,7 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 
        /* 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 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm,
        struct mem_cgroup *mem;
        int ret;
 
+       *ptr = NULL;
+
        if (mem_cgroup_disabled())
                return 0;
 
@@ -2916,6 +2918,8 @@ int mem_cgroup_prepare_migration(struct page *page,
        enum charge_type ctype;
        int ret = 0;
 
+       *ptr = NULL;
+
        VM_BUG_ON(PageTransHuge(page));
        if (mem_cgroup_disabled())
                return 0;
@@ -3058,7 +3062,7 @@ int mem_cgroup_shmem_charge_fallback(struct page *page,
                            struct mm_struct *mm,
                            gfp_t gfp_mask)
 {
-       struct mem_cgroup *mem = NULL;
+       struct mem_cgroup *mem;
        int ret;
 
        if (mem_cgroup_disabled())

diff --git a/mm/memory.c b/mm/memory.c
index 615be5127ce1f2895da610978c7d73ec9789308d..20d5f7499ce25cec556e60ba9932efd648ecad46 100644 (file)
--- 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;
 

diff --git a/mm/migrate.c b/mm/migrate.c
index 89e5c3fe8bbca2cc1a325abe080953d3b1ef6208..b0406d739ea7a07b282e3e65a387a31770b40d11 100644 (file)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -633,7 +633,7 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
        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)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 71b42ec55b783039b020cfeb3b410121b8a15fc0..039e61677635a815e8165b365f521034dd20bf95 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -880,7 +880,7 @@ unsigned int count_swap_pages(int type, int free)
 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;