netdev - Re: [PATCH v2 2/2] net: add trace events for net

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Date:   Tue, 12 Nov 2019 08:27:31 -0700
From:   David Ahern <dsahern@...il.com>
To:     Tony Lu <tonylu@...ux.alibaba.com>, davem@...emloft.net
Cc:     xiyou.wangcong@...il.com, eric.dumazet@...il.com,
        shemminger@...l.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] net: add trace events for net_device refcnt

On 11/12/19 6:05 AM, Tony Lu wrote:
> diff --git a/include/trace/events/net.h b/include/trace/events/net.h
> index 3b28843652d2..3bf6dd738882 100644
> --- a/include/trace/events/net.h
> +++ b/include/trace/events/net.h
> @@ -326,6 +326,47 @@ DEFINE_EVENT(net_dev_rx_exit_template, netif_receive_skb_list_exit,
>  	TP_ARGS(ret)
>  );
>  
> +DECLARE_EVENT_CLASS(net_dev_refcnt_template,
> +
> +	TP_PROTO(struct net_device *dev, void *location),
> +
> +	TP_ARGS(dev, location),
> +
> +	TP_STRUCT__entry(
> +		__string(	name,		dev->name	)
> +		__field(	int,		refcnt		)
> +		__field(	void *,		location	)
> +	),
> +
> +	TP_fast_assign(
> +		int i, refcnt = 0;
> +
> +		for_each_possible_cpu(i)
> +			refcnt += *per_cpu_ptr(dev->pcpu_refcnt, i);

Rather than copying the definition of netdev_refcnt_read here, so just
use it.

> +
> +		__assign_str(name, dev->name);
> +		__entry->refcnt = refcnt;
> +		__entry->location = location;
> +	),
> +
> +	TP_printk("dev=%s refcnt=%d location=%p",
> +		__get_str(name), __entry->refcnt, __entry->location)
> +);
> +
> +DEFINE_EVENT(net_dev_refcnt_template, net_dev_put,
> +
> +	TP_PROTO(struct net_device *dev, void *location),
> +
> +	TP_ARGS(dev, location)
> +);
> +
> +DEFINE_EVENT(net_dev_refcnt_template, net_dev_hold,
> +
> +	TP_PROTO(struct net_device *dev, void *location),
> +
> +	TP_ARGS(dev, location)
> +);
> +
>  #endif /* _TRACE_NET_H */
>  

The location alone does nothing for resolving reference count leaks; you
really have to use stack traces to pair up the hold and put and to give
context for what are repetitive locations for the hold and put.