netdev - Question on dev_kfree_skb(): why it is consume

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Date:   Mon, 28 Feb 2022 08:23:09 -0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     netdev <netdev@...r.kernel.org>
Subject: Question on dev_kfree_skb(): why it is consume_skb()?

Hello,

While the dev_kfree_skb() is used to track the dropped sk_buff, is there any
reason that it is consume_skb() ...

1328 #define dev_kfree_skb(a)        consume_skb(a)

890 void consume_skb(struct sk_buff *skb)
891 {
892         if (!skb_unref(skb))
893                 return;
894
895         trace_consume_skb(skb);
896         __kfree_skb(skb);
897 }

... but not kfree_skb()?

752 void kfree_skb(struct sk_buff *skb)
753 {
754         if (!skb_unref(skb))
755                 return;
756
757         trace_kfree_skb(skb, __builtin_return_address(0));
758         __kfree_skb(skb);
759 }
760 EXPORT_SYMBOL(kfree_skb);

I assume we may need kfree_skb() to track the dropped sk_buff.

In addition, there are places like __dev_kfree_skb_any() that may not capture
'SKB_REASON_DROPPED', if dev_kfree_skb() is equivalent to consume_skb().

3053 void __dev_kfree_skb_any(struct sk_buff *skb, enum skb_free_reason reason)
3054 {
3055         if (in_hardirq() || irqs_disabled())
3056                 __dev_kfree_skb_irq(skb, reason);
3057         else
3058                 dev_kfree_skb(skb);
3059 }
3060 EXPORT_SYMBOL(__dev_kfree_skb_any);

We may change like below?

diff --git a/net/core/dev.c b/net/core/dev.c
index 2d6771075720..0800e1c4b514 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3054,8 +3054,10 @@ void __dev_kfree_skb_any(struct sk_buff *skb, enum
skb_free_reason reason)
 {
 	if (in_hardirq() || irqs_disabled())
 		__dev_kfree_skb_irq(skb, reason);
-	else
+	else if (reason == SKB_REASON_CONSUMED)
 		dev_kfree_skb(skb);
+	else if (reason == SKB_REASON_DROPPED)
+		kfree_skb(skb);
 }
 EXPORT_SYMBOL(__dev_kfree_skb_any);

Thank you very much!

Dongli Zhang