linux-kernel - Re: [PATCH net 3/3] net: skb_queue_purge(): lock/unlock the queue only once

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Message-ID: <20171001175909.4b9e53d8@xeon-e3>
Date:   Sun, 1 Oct 2017 17:59:09 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Michael Witten <mfwitten@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 3/3] net: skb_queue_purge(): lock/unlock the queue
 only once

On Sun, 01 Oct 2017 22:19:20 -0000
Michael Witten <mfwitten@...il.com> wrote:

> +	spin_lock_irqsave(&q->lock, flags);
> +	skb = q->next;
> +	__skb_queue_head_init(q);
> +	spin_unlock_irqrestore(&q->lock, flags);

Other code manipulating lists uses splice operation and
a sk_buff_head temporary on the stack. That would be easier
to understand.

	struct sk_buf_head head;

	__skb_queue_head_init(&head);
	spin_lock_irqsave(&q->lock, flags);
	skb_queue_splice_init(q, &head);
	spin_unlock_irqrestore(&q->lock, flags);


> +	while (skb != head) {
> +		next = skb->next;
>  		kfree_skb(skb);
> +		skb = next;
> +	}

It would be cleaner if you could use
skb_queue_walk_safe rather than open coding the loop.

	skb_queue_walk_safe(&head, skb,  tmp)
		kfree_skb(skb);