memcg: avoid use cmpxchg in swap cgroup maintainance

swap_cgroup uses 2bytes data and uses cmpxchg in a new operation.  2byte
cmpxchg/xchg is not available on some archs.  This patch replaces
cmpxchg/xchg with operations under lock.

Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Reported-by: Sachin Sant <[email protected]> wrote:
Acked-by: Balbir Singh <[email protected]>
Acked-by: Daisuke Nishimura <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
index 3dd88539a0e6b47876ec87a91ee093533e1392c9..6c0081441a326a174f83ebd66485bd9cb961f88d 100644 (file)
--- a/mm/page_cgroup.c
+++ b/mm/page_cgroup.c
@@ -284,6 +284,7 @@ static DEFINE_MUTEX(swap_cgroup_mutex);
 struct swap_cgroup_ctrl {
        struct page **map;
        unsigned long length;
+       spinlock_t      lock;
 };
 
 struct swap_cgroup_ctrl swap_cgroup_ctrl[MAX_SWAPFILES];
@@ -353,16 +354,22 @@ unsigned short swap_cgroup_cmpxchg(swp_entry_t ent,
        struct swap_cgroup_ctrl *ctrl;
        struct page *mappage;
        struct swap_cgroup *sc;
+       unsigned long flags;
+       unsigned short retval;
 
        ctrl = &swap_cgroup_ctrl[type];
 
        mappage = ctrl->map[idx];
        sc = page_address(mappage);
        sc += pos;
-       if (cmpxchg(&sc->id, old, new) == old)
-               return old;
+       spin_lock_irqsave(&ctrl->lock, flags);
+       retval = sc->id;
+       if (retval == old)
+               sc->id = new;
        else
-               return 0;
+               retval = 0;
+       spin_unlock_irqrestore(&ctrl->lock, flags);
+       return retval;
 }
 
 /**
@@ -383,13 +390,17 @@ unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
        struct page *mappage;
        struct swap_cgroup *sc;
        unsigned short old;
+       unsigned long flags;
 
        ctrl = &swap_cgroup_ctrl[type];
 
        mappage = ctrl->map[idx];
        sc = page_address(mappage);
        sc += pos;
-       old = xchg(&sc->id, id);
+       spin_lock_irqsave(&ctrl->lock, flags);
+       old = sc->id;
+       sc->id = id;
+       spin_unlock_irqrestore(&ctrl->lock, flags);
 
        return old;
 }
@@ -441,6 +452,7 @@ int swap_cgroup_swapon(int type, unsigned long max_pages)
        mutex_lock(&swap_cgroup_mutex);
        ctrl->length = length;
        ctrl->map = array;
+       spin_lock_init(&ctrl->lock);
        if (swap_cgroup_prepare(type)) {
                /* memory shortage */
                ctrl->map = NULL;