netdev - Re: [patch net-next 03/12] ipmr: Add FIB notification access functions

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Date:   Thu, 21 Sep 2017 14:19:10 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Jiri Pirko <jiri@...nulli.us>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, yotamg@...lanox.com, idosch@...lanox.com,
        mlxsw@...lanox.com
Subject: Re: [patch net-next 03/12] ipmr: Add FIB notification access
 functions

On 21/09/17 09:43, Jiri Pirko wrote:
> From: Yotam Gigi <yotamg@...lanox.com>
> 
> Make the ipmr module register as a FIB notifier. To do that, implement both
> the ipmr_seq_read and ipmr_dump ops.
> 
> The ipmr_seq_read op returns a sequence counter that is incremented on
> every notification related operation done by the ipmr. To implement that,
> add a sequence counter in the netns_ipv4 struct and increment it whenever a
> new MFC route or VIF are added or deleted. The sequence operations are
> protected by the RTNL lock.
> 
> The ipmr_dump iterates the list of MFC routes and the list of VIF entries
> and sends notifications about them. The entries dump is done under RCU.
> 
> Signed-off-by: Yotam Gigi <yotamg@...lanox.com>
> Reviewed-by: Ido Schimmel <idosch@...lanox.com>
> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
> ---
>  include/linux/mroute.h   |  15 ++++++
>  include/net/netns/ipv4.h |   3 ++
>  net/ipv4/ipmr.c          | 135 ++++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 151 insertions(+), 2 deletions(-)
> 
[snip]
> +
> +static int ipmr_dump(struct net *net, struct notifier_block *nb)
> +{
> +	struct mr_table *mrt;
> +	int err;
> +
> +	err = ipmr_rules_dump(net, nb);
> +	if (err)
> +		return err;
> +
> +	ipmr_for_each_table(mrt, net) {
> +		struct vif_device *v = &mrt->vif_table[0];
> +		struct mfc_cache *mfc;
> +		int vifi;
> +
> +		/* Notifiy on table VIF entries */
> +		for (vifi = 0; vifi < mrt->maxvif; vifi++, v++) {
> +			if (!v->dev)
> +				continue;
> +
> +			call_ipmr_vif_entry_notifier(nb, net, FIB_EVENT_VIF_ADD,
> +						     v, vifi, mrt->id);
> +		}

The VIF table is protected by mrt_lock (rwlock), here with RCU only
you're not guaranteed to keep v->dev. It can become NULL after the check above.
For details you can see vif_delete() in net/ipv4/ipmr.c. You need at least
mrt_lock for reading.

> +
> +		/* Notify on table MFC entries */
> +		list_for_each_entry_rcu(mfc, &mrt->mfc_cache_list, list)
> +			call_ipmr_mfc_entry_notifier(nb, net,
> +						     FIB_EVENT_ENTRY_ADD, mfc,
> +						     mrt->id);
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct fib_notifier_ops ipmr_notifier_ops_template = {
> +	.family		= RTNL_FAMILY_IPMR,
> +	.fib_seq_read	= ipmr_seq_read,
> +	.fib_dump	= ipmr_dump,
> +	.owner		= THIS_MODULE,
> +};
> +
> +int __net_init ipmr_notifier_init(struct net *net)
> +{
> +	struct fib_notifier_ops *ops;
> +
> +	net->ipv4.ipmr_seq = 0;
> +
> +	ops = fib_notifier_ops_register(&ipmr_notifier_ops_template, net);
> +	if (IS_ERR(ops))
> +		return PTR_ERR(ops);
> +	net->ipv4.ipmr_notifier_ops = ops;
> +
> +	return 0;
> +}
> +
> +static void __net_exit ipmr_notifier_exit(struct net *net)
> +{
> +	fib_notifier_ops_unregister(net->ipv4.ipmr_notifier_ops);
> +	net->ipv4.ipmr_notifier_ops = NULL;
> +}
> +
>  /* Setup for IP multicast routing */
>  static int __net_init ipmr_net_init(struct net *net)
>  {
>  	int err;
>  
> +	err = ipmr_notifier_init(net);
> +	if (err)
> +		goto ipmr_notifier_fail;
> +
>  	err = ipmr_rules_init(net);
>  	if (err < 0)
> -		goto fail;
> +		goto ipmr_rules_fail;
>  
>  #ifdef CONFIG_PROC_FS
>  	err = -ENOMEM;
> @@ -3074,7 +3202,9 @@ static int __net_init ipmr_net_init(struct net *net)
>  proc_vif_fail:
>  	ipmr_rules_exit(net);
>  #endif
> -fail:
> +ipmr_rules_fail:
> +	ipmr_notifier_exit(net);
> +ipmr_notifier_fail:
>  	return err;
>  }
>  
> @@ -3084,6 +3214,7 @@ static void __net_exit ipmr_net_exit(struct net *net)
>  	remove_proc_entry("ip_mr_cache", net->proc_net);
>  	remove_proc_entry("ip_mr_vif", net->proc_net);
>  #endif
> +	ipmr_notifier_exit(net);
>  	ipmr_rules_exit(net);
>  }
>  
>