JoonSoo Kim Messages: 9 Registered: September 2012
Junior Member
2012/10/19 Glauber Costa <glommer@parallels.com>:
> +void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
> +{
> + struct kmem_cache *c;
> + int i;
> +
> + if (!s->memcg_params)
> + return;
> + if (!s->memcg_params->is_root_cache)
> + return;
> +
> + /*
> + * If the cache is being destroyed, we trust that there is no one else
> + * requesting objects from it. Even if there are, the sanity checks in
> + * kmem_cache_destroy should caught this ill-case.
> + *
> + * Still, we don't want anyone else freeing memcg_caches under our
> + * noses, which can happen if a new memcg comes to life. As usual,
> + * we'll take the set_limit_mutex to protect ourselves against this.
> + */
> + mutex_lock(&set_limit_mutex);
> + for (i = 0; i < memcg_limited_groups_array_size; i++) {
> + c = s->memcg_params->memcg_caches[i];
> + if (c)
> + kmem_cache_destroy(c);
> + }
> + mutex_unlock(&set_limit_mutex);
> +}
It may cause NULL deref.
Look at the following scenario.
1. some memcg slab caches has remained object.
2. start to destroy memcg.
3. schedule_delayed_work(kmem_cache_destroy_work_func, @delay 60hz)
4. all remained object is freed.
5. start to destroy root cache.
6. kmem_cache_destroy makes 's->memcg_params->memcg_caches[i]" NULL!!
7. Start delayed work function.
8. cachep in kmem_cache_destroy_work_func() may be NULL
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