netdev - Re: [PATCH v3] net: Add trace events for all receive exit points

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Date:   Fri, 16 Nov 2018 19:50:36 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     gbastien@...satic.net
Cc:     netdev@...r.kernel.org, mathieu.desnoyers@...icios.com,
        rostedt@...dmis.org, mingo@...hat.com
Subject: Re: [PATCH v3] net: Add trace events for all receive exit points

From: Geneviève Bastien <gbastien@...satic.net>
Date: Tue, 13 Nov 2018 15:13:26 -0500

> @@ -5222,9 +5228,14 @@ static void netif_receive_skb_list_internal(struct list_head *head)
>   */
>  int netif_receive_skb(struct sk_buff *skb)
>  {
> +	int ret;
> +
>  	trace_netif_receive_skb_entry(skb);
>  
> -	return netif_receive_skb_internal(skb);
> +	ret = netif_receive_skb_internal(skb);
> +	trace_netif_receive_skb_exit(skb, ret);

Every time I read this code from now on I'm going to say to myself
"oh crap, we reference 'skb' after it's potentially freed up"

I really don't like this.

I know only the pointer is used, but that pointer can be reallocated
to another SLAB object, even another SKB, by the time these exit
tracepoints execute.

Sorry, I can't really convince myself to apply this now.