Quoting Ben Blum (bblum@xxxxxxxxxx):
...
> +static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp,
> + enum cgroup_filetype type)
> +{
> + struct cgroup_pidlist *l;
> + /* don't need task_nsproxy() if we're looking at ourself */
> + struct pid_namespace *ns = get_pid_ns(current->nsproxy->pid_ns);
> + /*
> + * We can't drop the pidlist_mutex before taking the l->mutex in case
> + * the last ref-holder is trying to remove l from the list at the same
> + * time. Holding the pidlist_mutex precludes somebody taking whichever
> + * list we find out from under us - compare release_pid_array().
> + */
> + mutex_lock(&cgrp->pidlist_mutex);
> + list_for_each_entry(l, &cgrp->pidlists, links) {
> + if (l->key.type == type && l->key.ns == ns) {
> + /* found a matching list - drop the extra refcount */
> + put_pid_ns(ns);
> + /* make sure l doesn't vanish out from under us */
> + down_write(&l->mutex);
> + mutex_unlock(&cgrp->pidlist_mutex);
> + l->use_count++;
> + return l;
> + }
> + }
> + /* entry not found; create a new one */
> + l = kmalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL);
> + if (!l) {
> + mutex_unlock(&cgrp->pidlist_mutex);
Again, you need to put_pid_ns(ns) here.
> + return l;
> + }
> + init_rwsem(&l->mutex);
> + down_write(&l->mutex);
> + l->key.type = type;
> + l->key.ns = ns;
> + l->use_count = 0; /* don't increment here */
> + l->list = NULL;
> + l->owner = cgrp;
> + list_add(&l->links, &cgrp->pidlists);
> + mutex_unlock(&cgrp->pidlist_mutex);
> + return l;
> +}
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