netdev - Re: RFC: mac802154 Packet Queueing and Slave Devices

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Message-ID: <1347257547.1234.1110.camel@edumazet-glaptop>
Date:	Mon, 10 Sep 2012 08:12:27 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alan Ott <alan@...nal11.us>
Cc:	Alexander Smirnov <alex.bluesman.smirnov@...il.com>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	slapin@...fans.org, Tony Cheneau <tony.cheneau@...esiak.org>,
	linux-zigbee-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: RFC: mac802154 Packet Queueing and Slave Devices

On Sun, 2012-09-09 at 20:43 -0400, Alan Ott wrote:
> Hi,
> 
> Tony and I were recently talking about packet queueing on 802.15.4. What
> currently happens (in net/mac802154/tx.c) is that each tx packet (skb)
> is stuck on a work queue, and the worker function then sends each packet
> to the hardware driver in order.
> 
> The problem with this is that it defeats the netif flow control.

And qdisc ability to better control bufferbloat...

By the way, mac802154_tx() looks buggy :

if (!(priv->phy->channels_supported[page] & (1 << chan))) {
	WARN_ON(1);
	// Here, a kfree_skb(skb) is missing.
	return NETDEV_TX_OK;
}
if (skb_cow_head(skb, priv->hw.extra_tx_headroom)) {
	dev_kfree_skb(skb);  // should be kfree_skb(skb)
	return NETDEV_TX_OK;
}
work = kzalloc(sizeof(struct xmit_work), GFP_ATOMIC);
if (!work)
	return NETDEV_TX_BUSY;

NETDEV_TX_BUSY is going to loop. So if there is really no more memory,
its a deadlock. You should instead kfree_skb(skb) and return
NETDEV_TX_OK.

Also mac802154_wpan_xmit() returns NETDEV_TX_OK without kfree_skb(skb)
here :

if (chan == MAC802154_CHAN_NONE ||
    page >= WPAN_NUM_PAGES ||
    chan >= WPAN_NUM_CHANNELS)
	return NETDEV_TX_OK;



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