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SubjectRe: [PATCH] net: Convert net_mutex into rw_semaphore and down read it on net->init/->exit
On Tue, Nov 14, 2017 at 5:53 AM, Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
> @@ -406,7 +406,7 @@ struct net *copy_net_ns(unsigned long flags,
>
> get_user_ns(user_ns);
>
> - rv = mutex_lock_killable(&net_mutex);
> + rv = down_read_killable(&net_sem);
> if (rv < 0) {
> net_free(net);
> dec_net_namespaces(ucounts);
> @@ -421,7 +421,7 @@ struct net *copy_net_ns(unsigned long flags,
> list_add_tail_rcu(&net->list, &net_namespace_list);
> rtnl_unlock();
> }
> - mutex_unlock(&net_mutex);
> + up_read(&net_sem);
> if (rv < 0) {
> dec_net_namespaces(ucounts);
> put_user_ns(user_ns);
> @@ -446,7 +446,7 @@ static void cleanup_net(struct work_struct *work)
> list_replace_init(&cleanup_list, &net_kill_list);
> spin_unlock_irq(&cleanup_list_lock);
>
> - mutex_lock(&net_mutex);
> + down_read(&net_sem);
>
> /* Don't let anyone else find us. */
> rtnl_lock();
> @@ -486,7 +486,7 @@ static void cleanup_net(struct work_struct *work)
> list_for_each_entry_reverse(ops, &pernet_list, list)
> ops_free_list(ops, &net_exit_list);
>
> - mutex_unlock(&net_mutex);
> + up_read(&net_sem);

After your patch setup_net() could run concurrently with cleanup_net(),
given that ops_exit_list() is called on error path of setup_net() too,
it means ops->exit() now could run concurrently if it doesn't have its
own lock. Not sure if this breaks any existing user.

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