1 files changed, 56 insertions, 12 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e74d7080ec9e..9a6a51a7c416 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4077,14 +4077,14 @@ static struct cftype mem_cgroup_legacy_files[] = {
 
 static DEFINE_IDR(mem_cgroup_idr);
 
-static void mem_cgroup_id_get(struct mem_cgroup *memcg)
+static void mem_cgroup_id_get_many(struct mem_cgroup *memcg, unsigned int n)
 {
-        atomic_inc(&memcg->id.ref);
+        atomic_add(n, &memcg->id.ref);
 }
 
-static void mem_cgroup_id_put(struct mem_cgroup *memcg)
+static void mem_cgroup_id_put_many(struct mem_cgroup *memcg, unsigned int n)
 {
-        if (atomic_dec_and_test(&memcg->id.ref)) {
+        if (atomic_sub_and_test(n, &memcg->id.ref)) {
                 idr_remove(&mem_cgroup_idr, memcg->id.id);
                 memcg->id.id = 0;
 
@@ -4093,6 +4093,16 @@ static void mem_cgroup_id_put(struct mem_cgroup *memcg)
         }
 }
 
+static inline void mem_cgroup_id_get(struct mem_cgroup *memcg)
+{
+        mem_cgroup_id_get_many(memcg, 1);
+}
+
+static inline void mem_cgroup_id_put(struct mem_cgroup *memcg)
+{
+        mem_cgroup_id_put_many(memcg, 1);
+}
+
 /**
  * mem_cgroup_from_id - look up a memcg from a memcg id
  * @id: the memcg id to look up
@@ -4727,6 +4737,8 @@ static void __mem_cgroup_clear_mc(void)
                 if (!mem_cgroup_is_root(mc.from))
                         page_counter_uncharge(&mc.from->memsw, mc.moved_swap);
 
+                mem_cgroup_id_put_many(mc.from, mc.moved_swap);
+
                 /*
                  * we charged both to->memory and to->memsw, so we
                  * should uncharge to->memory.
@@ -4734,9 +4746,9 @@ static void __mem_cgroup_clear_mc(void)
                 if (!mem_cgroup_is_root(mc.to))
                         page_counter_uncharge(&mc.to->memory, mc.moved_swap);
 
-                css_put_many(&mc.from->css, mc.moved_swap);
+                mem_cgroup_id_get_many(mc.to, mc.moved_swap);
+                css_put_many(&mc.to->css, mc.moved_swap);
 
-                /* we've already done css_get(mc.to) */
                 mc.moved_swap = 0;
         }
         memcg_oom_recover(from);
@@ -5791,6 +5803,24 @@ static int __init mem_cgroup_init(void)
 subsys_initcall(mem_cgroup_init);
 
 #ifdef CONFIG_MEMCG_SWAP
+static struct mem_cgroup *mem_cgroup_id_get_online(struct mem_cgroup *memcg)
+{
+        while (!atomic_inc_not_zero(&memcg->id.ref)) {
+                /*
+                 * The root cgroup cannot be destroyed, so it's refcount must
+                 * always be >= 1.
+                 */
+                if (WARN_ON_ONCE(memcg == root_mem_cgroup)) {
+                        VM_BUG_ON(1);
+                        break;
+                }
+                memcg = parent_mem_cgroup(memcg);
+                if (!memcg)
+                        memcg = root_mem_cgroup;
+        }
+        return memcg;
+}
+
 /**
  * mem_cgroup_swapout - transfer a memsw charge to swap
  * @page: page whose memsw charge to transfer
@@ -5800,7 +5830,7 @@ subsys_initcall(mem_cgroup_init);
  */
 void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
 {
-        struct mem_cgroup *memcg;
+        struct mem_cgroup *memcg, *swap_memcg;
         unsigned short oldid;
 
         VM_BUG_ON_PAGE(PageLRU(page), page);
@@ -5815,16 +5845,27 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
         if (!memcg)
                 return;
 
-        mem_cgroup_id_get(memcg);
-        oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
+        /*
+         * In case the memcg owning these pages has been offlined and doesn't
+         * have an ID allocated to it anymore, charge the closest online
+         * ancestor for the swap instead and transfer the memory+swap charge.
+         */
+        swap_memcg = mem_cgroup_id_get_online(memcg);
+        oldid = swap_cgroup_record(entry, mem_cgroup_id(swap_memcg));
         VM_BUG_ON_PAGE(oldid, page);
-        mem_cgroup_swap_statistics(memcg, true);
+        mem_cgroup_swap_statistics(swap_memcg, true);
 
         page->mem_cgroup = NULL;
 
         if (!mem_cgroup_is_root(memcg))
                 page_counter_uncharge(&memcg->memory, 1);
 
+        if (memcg != swap_memcg) {
+                if (!mem_cgroup_is_root(swap_memcg))
+                        page_counter_charge(&swap_memcg->memsw, 1);
+                page_counter_uncharge(&memcg->memsw, 1);
+        }
+
         /*
          * Interrupts should be disabled here because the caller holds the
          * mapping->tree_lock lock which is taken with interrupts-off. It is
@@ -5863,11 +5904,14 @@ int mem_cgroup_try_charge_swap(struct page *page, swp_entry_t entry)
         if (!memcg)
                 return 0;
 
+        memcg = mem_cgroup_id_get_online(memcg);
+
         if (!mem_cgroup_is_root(memcg) &&
-            !page_counter_try_charge(&memcg->swap, 1, &counter))
+            !page_counter_try_charge(&memcg->swap, 1, &counter)) {
+                mem_cgroup_id_put(memcg);
                 return -ENOMEM;
+        }
 
-        mem_cgroup_id_get(memcg);
         oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
         VM_BUG_ON_PAGE(oldid, page);
         mem_cgroup_swap_statistics(memcg, true);