> Index: mmotm-0811/mm/memcontrol.c
> ===================================================================
> --- mmotm-0811.orig/mm/memcontrol.c
> +++ mmotm-0811/mm/memcontrol.c
> @@ -195,6 +195,7 @@ static void mem_cgroup_oom_notify(struct
> */
> struct mem_cgroup {
> struct cgroup_subsys_state css;
> + int valid; /* for checking validness under RCU access.*/
> /*
> * the counter to account for memory usage
> */
Do we really need to add this new member ?
Can't we safely access "mem(=rcu_dereference(mem_cgroup[id]))" under rcu_read_lock() ?
(iow, "mem" is not freed ?)
> @@ -4049,6 +4068,7 @@ static void __mem_cgroup_free(struct mem
> mem_cgroup_remove_from_trees(mem);
> free_css_id(&mem_cgroup_subsys, &mem->css);
>
> + atomic_dec(&mem_cgroup_num);
> for_each_node_state(node, N_POSSIBLE)
> free_mem_cgroup_per_zone_info(mem, node);
>
> @@ -4059,6 +4079,19 @@ static void __mem_cgroup_free(struct mem
> vfree(mem);
> }
>
> +static void mem_cgroup_free(struct mem_cgroup *mem)
> +{
> + /* No more lookup */
> + mem->valid = 0;
> + rcu_assign_pointer(mem_cgroups[css_id(&mem->css)], NULL);
> + /*
> + * Because we call vfree() etc...use synchronize_rcu() rather than
> + * call_rcu();
> + */
> + synchronize_rcu();
> + __mem_cgroup_free(mem);
> +}
> +
> static void mem_cgroup_get(struct mem_cgroup *mem)
> {
> atomic_inc(&mem->refcnt);
> @@ -4068,7 +4101,7 @@ static void __mem_cgroup_put(struct mem_
> {
> if (atomic_sub_and_test(count, &mem->refcnt)) {
> struct mem_cgroup *parent = parent_mem_cgroup(mem);
> - __mem_cgroup_free(mem);
> + mem_cgroup_free(mem);
> if (parent)
> mem_cgroup_put(parent);
> }
> @@ -4189,9 +4222,11 @@ mem_cgroup_create(struct cgroup_subsys *
> atomic_set(&mem->refcnt, 1);
> mem->move_charge_at_immigrate = 0;
> mutex_init(&mem->thresholds_lock);
> + atomic_inc(&mem_cgroup_num);
> + register_memcg_id(mem);
> return &mem->css;
> free_out:
> - __mem_cgroup_free(mem);
> + mem_cgroup_free(mem);
> root_mem_cgroup = NULL;
> return ERR_PTR(error);
> }
I think mem_cgroup_num should be increased at mem_cgroup_alloc(), because it
is decreased at __mem_cgroup_free(). Otherwise, it can be decreased while it
has not been increased, if mem_cgroup_create() fails after mem_cgroup_alloc().
Thanks,
Daisuke Nishimura.
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