netdev - Re: [PATCH bpf v2] xdp: fix hang while unregistering device bound to xdp socket

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Message-ID: <d8b2bc92-3b7e-dfe7-35ee-61a68d46ff02@samsung.com>
Date:   Mon, 10 Jun 2019 11:05:41 +0300
From:   Ilya Maximets <i.maximets@...sung.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, xdp-newbies@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Subject: Re: [PATCH bpf v2] xdp: fix hang while unregistering device bound
 to xdp socket

On 08.06.2019 2:31, Jakub Kicinski wrote:
> On Fri,  7 Jun 2019 20:31:43 +0300, Ilya Maximets wrote:
>> +static int xsk_notifier(struct notifier_block *this,
>> +			unsigned long msg, void *ptr)
>> +{
>> +	struct sock *sk;
>> +	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
>> +	struct net *net = dev_net(dev);
>> +	int i, unregister_count = 0;
> 
> Please order the var declaration lines longest to shortest.
> (reverse christmas tree)

Hi.
I'm not a fan of mixing 'struct's with bare types in the declarations.
Moving the 'sk' to the third place will make a hole like this:

	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct net *net = dev_net(dev);
	struct sock *sk;
	int i, unregister_count = 0;

Which is not looking good.
Moving to the 4th place:

	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct net *net = dev_net(dev);
	int i, unregister_count = 0;
	struct sock *sk;

This variant doesn't look good for me because of mixing 'struct's with
bare integers.

Do you think I need to use one of above variants?

> 
>> +	mutex_lock(&net->xdp.lock);
>> +	sk_for_each(sk, &net->xdp.list) {
>> +		struct xdp_sock *xs = xdp_sk(sk);
>> +
>> +		mutex_lock(&xs->mutex);
>> +		switch (msg) {
>> +		case NETDEV_UNREGISTER:
> 
> You should probably check the msg type earlier and not take all the
> locks and iterate for other types..

Yeah. I thought about it too. Will fix in the next version.

Best regards, Ilya Maximets.