From: ebiederm@xmission•com (Eric W. Biederman)
To: Ying Xue <ying.xue@windriver•com>
Cc: <netdev@vger•kernel.org>, <cwang@twopensource•com>,
<herbert@gondor•apana.org.au>, <xemul@openvz•org>,
<davem@davemloft•net>, <eric.dumazet@gmail•com>,
<maxk@qti•qualcomm.com>, <stephen@networkplumber•org>,
<tgraf@suug•ch>, <nicolas.dichtel@6wind•com>,
<tom@herbertland•com>, <jchapman@katalix•com>,
<erik.hugne@ericsson•com>, <jon.maloy@ericsson•com>,
<horms@verge•net.au>
Subject: Re: [RFC PATCH net-next 00/11] netns: don't switch namespace while creating kernel sockets
Date: Fri, 08 May 2015 06:07:55 -0500 [thread overview]
Message-ID: <87a8xfba44.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <554C78BE.100@windriver.com> (Ying Xue's message of "Fri, 8 May 2015 16:50:06 +0800")
Ying Xue <ying.xue@windriver•com> writes:
> On 05/08/2015 12:14 AM, Eric W. Biederman wrote:
>> I agree that commit 23fe18669e7f ("[NETNS]: Fix race between put_net()
>> and netlink_kernel_create()." was a hack.
>>
>
> Thanks for the agreement :)
>
>> However it is not appropriate to call get_net on a network namespace
>> whose count might be zero.
>
> I will explain why it's still safe for us in another mail even if we do this.
>
> I believe all of your patches rely on that
>> currently.
>
> Yes, you are right.
>
> Instead we need to build something like sk_release_kernel
>> that does not increase the network namespace reference count
>
> Please refer to above comments.
>
> if you are
>> going to avoid changing the network namespace on a socket (a worthy
>> goal).
>>
>
> Thanks to the conformation for the effort!
>
>> The following change shows how it is possible to always know that your
>> network namespace has a non-zero reference count in the network
>> namespace initialization methods. My implementation of
>> lock_network_namespaces is problematic in that it does not sleep
>> while network namespaces are unregistering. But it is enough to show
>> how the locking and reference counting can be fixed.
>>
>
> If my understanding for your proposal is right, register_pernet_subsys() will
> return a failed error code to its caller if it's found that there is a net whose
> refcount is zero from net_namespace_list in lock_network_namespaces(), which
> means the per namespace operation is not registered at all in this situation.
> But in practice we should not reject the registration even if there is a dead
> net linked in the global net_namespace_list.
I agree which is why my implementation of lock_network_namespaces below
loops until there are no exiting network namespaces.
Eric
> Regards,
> Ying
>
>> Eric
>>
>>
>> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
>> index a3abb719221f..81c53ccc5764 100644
>> --- a/net/core/net_namespace.c
>> +++ b/net/core/net_namespace.c
>> @@ -822,6 +822,49 @@ static void unregister_pernet_operations(struct pernet_operations *ops)
>> ida_remove(&net_generic_ids, *ops->id);
>> }
>>
>> +static void unlock_network_namespaces(void)
>> +{
>> + /* Drop the reference count to every network namespace
>> + * and then release the net_mutex.
>> + */
>> + struct net *net;
>> +
>> + for_each_net(net)
>> + put_net(net);
>> +
>> + mutex_unlock(&net_mutex);
>> +}
>> +
>> +static void lock_network_namespaces(void)
>> +{
>> + /* Take the mutex lock ensuring no new network namespaces
>> + * and take a reference on all existing network namespaces
>> + * allowing network namespace initialization code to take
>> + * further references
>> + */
>> + for (;;) {
>> + struct net *net, *stop;
>> +
>> + mutex_lock(&net_mutex);
>> + for_each_net(net) {
>> + if (!maybe_get_net(net))
>> + goto undo;
>> + }
>> + return;
>> +undo:
>> + /* Remember the network namespace whose reference
>> + * count was not acquired. */
>> + stop = net;
>> + for_each_net(net) {
>> + if (net_eq(net, stop))
>> + goto undone;
>> + put_net(net);
>> + }
>> +undone:
>> + mutex_unlock(&net_mutex);
>> + }
>> +}
>> +
>> /**
>> * register_pernet_subsys - register a network namespace subsystem
>> * @ops: pernet operations structure for the subsystem
>> @@ -844,9 +887,9 @@ static void unregister_pernet_operations(struct pernet_operations *ops)
>> int register_pernet_subsys(struct pernet_operations *ops)
>> {
>> int error;
>> - mutex_lock(&net_mutex);
>> + lock_network_namespaces();
>> error = register_pernet_operations(first_device, ops);
>> - mutex_unlock(&net_mutex);
>> + unlock_network_namespaces();
>> return error;
>> }
>> EXPORT_SYMBOL_GPL(register_pernet_subsys);
>> @@ -890,11 +933,11 @@ EXPORT_SYMBOL_GPL(unregister_pernet_subsys);
>> int register_pernet_device(struct pernet_operations *ops)
>> {
>> int error;
>> - mutex_lock(&net_mutex);
>> + lock_network_namespaces();
>> error = register_pernet_operations(&pernet_list, ops);
>> if (!error && (first_device == &pernet_list))
>> first_device = &ops->list;
>> - mutex_unlock(&net_mutex);
>> + unlock_network_namespaces();
>> return error;
>> }
>> EXPORT_SYMBOL_GPL(register_pernet_device);
next prev parent reply other threads:[~2015-05-08 11:12 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-07 8:52 [RFC PATCH net-next 00/11] netns: don't switch namespace while creating kernel sockets Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 01/11] netns: Fix race between put_net() and netlink_kernel_create() Ying Xue
2015-05-07 9:04 ` Herbert Xu
2015-05-07 17:19 ` Cong Wang
2015-05-07 17:28 ` Eric W. Biederman
2015-05-08 11:20 ` Eric W. Biederman
2015-05-08 11:20 ` Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 02/11] netlink: avoid unnecessary namespace switch when create netlink kernel sockets Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 03/11] tun: avoid unnecessary namespace switch during kernel socket creation Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 04/11] inet: " Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 05/11] udp_tunnel: avoid to switch namespace for tunnel socket Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 06/11] ip6_udp_tunnel: " Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 07/11] l2tp: avoid to switch namespace for l2tp " Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 08/11] ipvs: avoid to switch namespace for ipvs kernel socket Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 09/11] tipc: fix net leak issue Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 10/11] tipc: remove sk_change_net interface Ying Xue
2015-05-07 8:52 ` [RFC PATCH net-next 11/11] net: change behaviours of functions of creating and releasing kernel sockets Ying Xue
2015-05-07 16:14 ` [RFC PATCH net-next 00/11] netns: don't switch namespace while creating " Eric W. Biederman
2015-05-07 18:19 ` Cong Wang
2015-05-07 18:26 ` Eric W. Biederman
2015-05-07 18:53 ` Cong Wang
2015-05-07 18:58 ` Eric W. Biederman
2015-05-07 19:29 ` Cong Wang
2015-05-07 20:01 ` Eric W. Biederman
2015-05-08 9:10 ` Ying Xue
2015-05-08 11:15 ` Eric W. Biederman
2015-05-08 8:50 ` Ying Xue
2015-05-08 9:25 ` Ying Xue
2015-05-08 11:07 ` Eric W. Biederman [this message]
2015-05-08 16:33 ` Cong Wang
2015-05-08 14:07 ` Herbert Xu
2015-05-08 17:36 ` Eric W. Biederman
2015-05-08 20:27 ` Cong Wang
2015-05-08 21:13 ` Cong Wang
2015-05-08 22:08 ` Eric W. Biederman
2015-05-09 1:13 ` Herbert Xu
2015-05-09 1:53 ` Eric W. Biederman
2015-05-09 2:05 ` [PATCH 0/6] Cleanup the " Eric W. Biederman
2015-05-09 2:07 ` [PATCH 1/6] tun: Utilize the normal socket network namespace refcounting Eric W. Biederman
2015-05-09 2:08 ` [PATCH 2/6] net: Add a struct net parameter to sock_create_kern Eric W. Biederman
2015-05-12 8:24 ` David Laight
2015-05-12 8:55 ` Eric W. Biederman
2015-05-12 11:48 ` David Laight
2015-05-12 12:28 ` Nicolas Dichtel
2015-05-12 13:16 ` David Laight
2015-05-12 14:15 ` Nicolas Dichtel
2015-05-12 15:58 ` Eric W. Biederman
2015-05-12 14:45 ` David Miller
2015-05-09 2:09 ` [PATCH 3/6] net: Pass kern from net_proto_family.create to sk_alloc Eric W. Biederman
2015-05-09 16:51 ` Eric Dumazet
2015-05-09 17:31 ` Eric W. Biederman
2015-05-09 2:10 ` [PATCH 4/6] net: Modify sk_alloc to not reference count the netns of kernel sockets Eric W. Biederman
2015-05-09 2:11 ` [PATCH 5/6] netlink: Create kernel netlink sockets in the proper network namespace Eric W. Biederman
2015-05-09 2:12 ` [PATCH 6/6] net: kill sk_change_net and sk_release_kernel Eric W. Biederman
2015-05-09 2:38 ` [PATCH 0/6] Cleanup the kernel sockets Herbert Xu
2015-05-11 14:53 ` David Miller
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