Re: [PATCH v2 net-next 1/3] net: skb: introduce kfree_skb_with_reason()

[Jakub Kicinski]

On Thu, 30 Dec 2021 17:32:38 +0800 menglong8.dong@xxxxxxxxx wrote:
> From: Menglong Dong <imagedong@xxxxxxxxxxx>
> 
> Introduce the interface kfree_skb_with_reason(), which is used to pass
> the reason why the skb is dropped to 'kfree_skb' tracepoint.
> 
> Add the 'reason' field to 'trace_kfree_skb', therefor user can get
> more detail information about abnormal skb with 'drop_monitor' or
> eBPF.

>  void skb_release_head_state(struct sk_buff *skb);
>  void kfree_skb(struct sk_buff *skb);

Should this be turned into a static inline calling
kfree_skb_with_reason() now? BTW you should drop the 
'_with'.

> +void kfree_skb_with_reason(struct sk_buff *skb,
> +			   enum skb_drop_reason reason);

continuation line is unaligned, please try checkpatch

>  void kfree_skb_list(struct sk_buff *segs);
>  void skb_dump(const char *level, const struct sk_buff *skb, bool full_pkt);
>  void skb_tx_error(struct sk_buff *skb);
> diff --git a/include/trace/events/skb.h b/include/trace/events/skb.h
> index 9e92f22eb086..cab1c08a30cd 100644
> --- a/include/trace/events/skb.h
> +++ b/include/trace/events/skb.h
> @@ -9,29 +9,51 @@
>  #include <linux/netdevice.h>
>  #include <linux/tracepoint.h>
>  
> +#define TRACE_SKB_DROP_REASON					\
> +	EM(SKB_DROP_REASON_NOT_SPECIFIED, NOT_SPECIFIED)	\
> +	EMe(SKB_DROP_REASON_MAX, HAHA_MAX)

HAHA_MAX ?

> +
> +#undef EM
> +#undef EMe
> +
> +#define EM(a, b)	TRACE_DEFINE_ENUM(a);
> +#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
> +
> +TRACE_SKB_DROP_REASON
> +
> +#undef EM
> +#undef EMe
> +#define EM(a, b)	{ a, #b },
> +#define EMe(a, b)	{ a, #b }
> +
> +

double new line

>  /*
>   * Tracepoint for free an sk_buff:
>   */
>  TRACE_EVENT(kfree_skb,
>  
> -	TP_PROTO(struct sk_buff *skb, void *location),
> +	TP_PROTO(struct sk_buff *skb, void *location,
> +		 enum skb_drop_reason reason),
>  
> -	TP_ARGS(skb, location),
> +	TP_ARGS(skb, location, reason),
>  
>  	TP_STRUCT__entry(
> -		__field(	void *,		skbaddr		)
> -		__field(	void *,		location	)
> -		__field(	unsigned short,	protocol	)
> +		__field(void *,		skbaddr)
> +		__field(void *,		location)
> +		__field(unsigned short,	protocol)
> +		__field(enum skb_drop_reason,	reason)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->skbaddr = skb;
>  		__entry->location = location;
>  		__entry->protocol = ntohs(skb->protocol);
> +		__entry->reason = reason;
>  	),
>  
> -	TP_printk("skbaddr=%p protocol=%u location=%p",
> -		__entry->skbaddr, __entry->protocol, __entry->location)
> +	TP_printk("skbaddr=%p protocol=%u location=%p reason: %s",
> +		__entry->skbaddr, __entry->protocol, __entry->location,
> +		__print_symbolic(__entry->reason, TRACE_SKB_DROP_REASON))
>  );
>  
>  TRACE_EVENT(consume_skb,
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 644b9c8be3a8..9464dbf9e3d6 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -4899,7 +4899,8 @@ static __latent_entropy void net_tx_action(struct softirq_action *h)
>  			if (likely(get_kfree_skb_cb(skb)->reason == SKB_REASON_CONSUMED))
>  				trace_consume_skb(skb);
>  			else
> -				trace_kfree_skb(skb, net_tx_action);
> +				trace_kfree_skb(skb, net_tx_action,
> +						SKB_DROP_REASON_NOT_SPECIFIED);
>  
>  			if (skb->fclone != SKB_FCLONE_UNAVAILABLE)
>  				__kfree_skb(skb);
> diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
> index 3d0ab2eec916..7b288a121a41 100644
> --- a/net/core/drop_monitor.c
> +++ b/net/core/drop_monitor.c
> @@ -110,7 +110,8 @@ static u32 net_dm_queue_len = 1000;
>  
>  struct net_dm_alert_ops {
>  	void (*kfree_skb_probe)(void *ignore, struct sk_buff *skb,
> -				void *location);
> +				void *location,
> +				enum skb_drop_reason reason);
>  	void (*napi_poll_probe)(void *ignore, struct napi_struct *napi,
>  				int work, int budget);
>  	void (*work_item_func)(struct work_struct *work);
> @@ -262,7 +263,9 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
>  	spin_unlock_irqrestore(&data->lock, flags);
>  }
>  
> -static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
> +static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb,
> +				void *location,
> +				enum skb_drop_reason reason)
>  {
>  	trace_drop_common(skb, location);
>  }
> @@ -490,7 +493,8 @@ static const struct net_dm_alert_ops net_dm_alert_summary_ops = {
>  
>  static void net_dm_packet_trace_kfree_skb_hit(void *ignore,
>  					      struct sk_buff *skb,
> -					      void *location)
> +					      void *location,
> +					      enum skb_drop_reason reason)
>  {
>  	ktime_t tstamp = ktime_get_real();
>  	struct per_cpu_dm_data *data;
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 275f7b8416fe..570dc022a8a1 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -770,11 +770,31 @@ void kfree_skb(struct sk_buff *skb)
>  	if (!skb_unref(skb))
>  		return;
>  
> -	trace_kfree_skb(skb, __builtin_return_address(0));
> +	trace_kfree_skb(skb, __builtin_return_address(0),
> +			SKB_DROP_REASON_NOT_SPECIFIED);
>  	__kfree_skb(skb);
>  }
>  EXPORT_SYMBOL(kfree_skb);
>  
> +/**
> + *	kfree_skb_with_reason - free an sk_buff with reason
> + *	@skb: buffer to free
> + *	@reason: reason why this skb is dropped
> + *
> + *	The same as kfree_skb() except that this function will pass
> + *	the drop reason to 'kfree_skb' tracepoint.
> + */
> +void kfree_skb_with_reason(struct sk_buff *skb,
> +			   enum skb_drop_reason reason)
> +{
> +	if (!skb_unref(skb))
> +		return;
> +
> +	trace_kfree_skb(skb, __builtin_return_address(0), reason);
> +	__kfree_skb(skb);
> +}
> +EXPORT_SYMBOL(kfree_skb_with_reason);
> +
>  void kfree_skb_list(struct sk_buff *segs)
>  {
>  	while (segs) {