linux-kernel - Re: [PATCH net-next v18 17/25] ovpn: implement keepalive mechanism

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Message-ID: <eb6bd31b-686b-4edc-bcdf-935cb452b271@openvpn.net>
Date: Mon, 3 Feb 2025 10:55:31 +0100
From: Antonio Quartulli <antonio@...nvpn.net>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Donald Hunter <donald.hunter@...il.com>, Shuah Khan <shuah@...nel.org>,
 ryazanov.s.a@...il.com, Andrew Lunn <andrew+netdev@...n.ch>,
 Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, Xiao Liang <shaw.leon@...il.com>
Subject: Re: [PATCH net-next v18 17/25] ovpn: implement keepalive mechanism

On 03/02/2025 10:20, Sabrina Dubroca wrote:
> 2025-01-13, 10:31:36 +0100, Antonio Quartulli wrote:
>> +void ovpn_xmit_special(struct ovpn_peer *peer, const void *data,
>> +		       const unsigned int len)
>> +{
>> +	struct ovpn_priv *ovpn;
>> +	struct sk_buff *skb;
>> +
>> +	ovpn = peer->ovpn;
>> +	if (unlikely(!ovpn))
>> +		return;
>> +
>> +	skb = alloc_skb(256 + len, GFP_ATOMIC);
>> +	if (unlikely(!skb))
>> +		return;
>> +
>> +	skb_reserve(skb, 128);
>> +	skb->priority = TC_PRIO_BESTEFFORT;
>> +	__skb_put_data(skb, data, len);
>> +
>> +	/* increase reference counter when passing peer to sending queue */
>> +	if (!ovpn_peer_hold(peer)) {
>> +		netdev_dbg(ovpn->dev,
>> +			   "cannot hold peer reference for sending special packet\n");
>> +		kfree_skb(skb);
>> +		return;
>> +	}
>> +
>> +	ovpn_send(ovpn, skb, peer);
>> +}
> 
> [...]
>> +static void ovpn_peer_keepalive_send(struct work_struct *work)
>> +{
>> +	struct ovpn_peer *peer = container_of(work, struct ovpn_peer,
>> +					      keepalive_work);
>> +
>> +	local_bh_disable();
>> +	ovpn_xmit_special(peer, ovpn_keepalive_message,
>> +			  sizeof(ovpn_keepalive_message));
>> +	local_bh_enable();
>> +	ovpn_peer_put(peer);
> 
> nit: could we simply drop this put and the hold in ovpn_xmit_special?
> ovpn_peer_keepalive_send has a reference on the peer from the WQ, just
> transfer it to ovpn_xmit_special and then ovpn_send. No need to
> pretend to acquire one for ovpn_send's sake and drop the one we got
> from the WQ? (ovpn_xmit_special would need to _put(peer) in case of
> early return)

Ok, will drop both and add a comment to remember the casual reader that 
we already hold a reference (+ put() in error path).

Regards,

> 
>> +}
> 

-- 
Antonio Quartulli
OpenVPN Inc.