net: do not delay zero-copy skbs in skb_attempt_defer_free()

After the blamed commit, TCP tx zero copy notifications could be
arbitrarily delayed and cause regressions in applications waiting
for them.

Signed-off-by: Eric Dumazet <[email protected]>
Fixes: e20dfba ("net: fix napi_consume_skb() with alien skbs")
Reviewed-by: Jason Xing <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: edumazet

net/core/skbuff.c

@@ -7266,10 +7266,15 @@ void skb_attempt_defer_free(struct sk_buff *skb)
 {
 	struct skb_defer_node *sdn;
 	unsigned long defer_count;
-	int cpu = skb->alloc_cpu;
 	unsigned int defer_max;
 	bool kick;
+	int cpu;
 
+	/* zero copy notifications should not be delayed. */
+	if (skb_zcopy(skb))
+		goto nodefer;
+
+	cpu = skb->alloc_cpu;
 	if (cpu == raw_smp_processor_id() ||
 	    WARN_ON_ONCE(cpu >= nr_cpu_ids) ||
 	    !cpu_online(cpu)) {