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

[Eric Dumazet <edumazet@google.com>]

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 <edumazet@google.com>
Fixes: e20dfbad8aab ("net: fix napi_consume_skb() with alien skbs")
---
 net/core/skbuff.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 699c401a5eae9c497a42b6bdd8593af7890529f4..dc47d3efc72ed86dce5e382d505eda7bc863669a 100644
--- a/net/core/skbuff.c
+++ b/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)) {
-- 
2.53.0.310.g728cabbaf7-goog