On 15.11.2017 06:19, Eric W. Biederman wrote: > Kirill Tkhai <ktk...@virtuozzo.com> writes: > >> On 14.11.2017 21:39, Cong Wang wrote: >>> On Tue, Nov 14, 2017 at 5:53 AM, Kirill Tkhai <ktk...@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. >> >> Yes, there will be possible concurrent ops->init() for a net namespace, >> and ops->exit() for another one. I hadn't found pernet operations, which >> have a problem with that. If they exist, they are hidden and not clear seen. >> The pernet operations in general do not touch someone else's memory. >> If suddenly there is one, KASAN should show it after a while. > > Certainly the use of hash tables shared between multiple network > namespaces would count. I don't rembmer how many of these we have but > there used to be quite a few.
Could you please provide an example of hash tables, you mean?