From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH] net: Convert net_mutex into rw_semaphore and down read it on net->init/->exit Date: Wed, 15 Nov 2017 10:31:11 -0600 Message-ID: <87r2sz33n4.fsf@xmission.com> References: <151066759055.14465.9783879083192000862.stgit@localhost.localdomain> <88152c11-a5b5-90f8-be46-99ed6c722064@virtuozzo.com> <87shdg8bzd.fsf@xmission.com> <8c808278-1925-37c0-619c-87bd1802790a@virtuozzo.com> <06b1d740-d443-ac23-a7b0-675e7b6ff6f9@virtuozzo.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Cong Wang , David Miller , vyasevic@redhat.com, kstewart@linuxfoundation.org, pombredanne@nexb.com, Vladislav Yasevich , mark.rutland@arm.com, Greg KH , Alexey Dobriyan , Florian Westphal , Nicolas Dichtel , roman.kapl@sysgo.com, Paul Moore , David Ahern , Daniel Borkmann , lucien xin , Matthias Schiffer , rshearma@brocade.com, LKML , Linux Kernel Network Developers , avagin@virtuozzo.com, gorcunov@virtuozzo.com To: Kirill Tkhai Return-path: In-Reply-To: <06b1d740-d443-ac23-a7b0-675e7b6ff6f9@virtuozzo.com> (Kirill Tkhai's message of "Wed, 15 Nov 2017 15:36:34 +0300") Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org Kirill Tkhai writes: > On 15.11.2017 12:51, Kirill Tkhai wrote: >> On 15.11.2017 06:19, Eric W. Biederman wrote: >>> Kirill Tkhai writes: >>> >>>> On 14.11.2017 21:39, Cong Wang wrote: >>>>> On Tue, Nov 14, 2017 at 5:53 AM, Kirill Tkhai 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? > > Ah, I see, it's dccp_hashinfo etc. The big one used to be the route cache. With resizable hash tables things may be getting better in that regard. Eric