Michal Hocko wrote:
> +bool task_has_external_users(struct task_struct *p)
> +{
> + struct mm_struct *mm = NULL;
> + struct task_struct *t;
> + int active_threads = 0;
> + bool ret = true; /* be pessimistic */
> +
> + rcu_read_lock();
> + for_each_thread(p, t) {
> + task_lock(t);
> + if (likely(t->mm)) {
> + active_threads++;
> + if (!mm) {
> + mm = t->mm;
> + atomic_inc(&mm->mm_count);
> + }
> + }
> + task_unlock(t);
> + }
> + rcu_read_unlock();
> +
I don't like this. We might sleep here long enough to change mm_users.
> + if (mm) {
> + if (atomic_read(&mm->mm_users) <= active_threads)
> + ret = false;
> + mmdrop(mm);
> + }
> + return ret;
> +}
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