From: ebiederm@xmission•com (Eric W. Biederman)
To: Fan Du <fan.du@windriver•com>
Cc: <serge.hallyn@canonical•com>, <davem@davemloft•net>,
<netdev@vger•kernel.org>
Subject: Re: [PATCH] net namespace: wrap for_each_net with rtnl_lock
Date: Thu, 04 Jul 2013 00:04:27 -0700 [thread overview]
Message-ID: <87txkaolfo.fsf@xmission.com> (raw)
In-Reply-To: <1372918855-3815-1-git-send-email-fan.du@windriver.com> (Fan Du's message of "Thu, 4 Jul 2013 14:20:55 +0800")
Fan Du <fan.du@windriver•com> writes:
> The read access to net_namespace_list with for_each_net should always
> be protected with rtnl_lock agiast any adding/removing operation from
> the list.
That is not correct. The rtnl_lock does not protect the
net_namespace_list. The net_mutex provides that protection.
Modifications to the net_namespace_list are under both the rtnl_lock
and the net_mutex which removes the need of grabbing the net_mutex when
you just need to traverse the list of network namespaces. This avoids a
lock ordering problem as most places it is desirable to traverse the
net namespace list the rtnl_lock is already held.
In general the init methods will deadlock if you call them with the
rtnl_lock held, as they grab the rtnl_lock when creating network devices
etc.
The methods you change are protected by the net_mutex so I don't see any
problems here.
Was this patch inspired by code review or was there an actual problem
that inspired it?
> Signed-off-by: Fan Du <fan.du@windriver•com>
> ---
> net/core/net_namespace.c | 4 ++++
> 1 files changed, 4 insertions(+), 0 deletions(-)
>
> diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
> index f976520..f3808ff 100644
> --- a/net/core/net_namespace.c
> +++ b/net/core/net_namespace.c
> @@ -445,12 +445,14 @@ static int __register_pernet_operations(struct list_head *list,
>
> list_add_tail(&ops->list, list);
> if (ops->init || (ops->id && ops->size)) {
> + rtnl_lock();
> for_each_net(net) {
> error = ops_init(ops, net);
> if (error)
> goto out_undo;
> list_add_tail(&net->exit_list, &net_exit_list);
> }
> + rtnl_unlock();
> }
> return 0;
>
> @@ -468,8 +470,10 @@ static void __unregister_pernet_operations(struct pernet_operations *ops)
> LIST_HEAD(net_exit_list);
>
> list_del(&ops->list);
> + rtnl_lock();
> for_each_net(net)
> list_add_tail(&net->exit_list, &net_exit_list);
> + rtnl_unlock();
> ops_exit_list(ops, &net_exit_list);
> ops_free_list(ops, &net_exit_list);
> }
next prev parent reply other threads:[~2013-07-04 7:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-04 6:20 [PATCH] net namespace: wrap for_each_net with rtnl_lock Fan Du
2013-07-04 7:04 ` Eric W. Biederman [this message]
2013-07-04 7:57 ` Fan Du
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