From 6de1dec1c166c7f7324ce52ccfdf43e2fa743b19 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 15 Oct 2025 05:27:15 +0000 Subject: [PATCH] udp: do not use skb_release_head_state() before skb_attempt_defer_free() Michal reported and bisected an issue after recent adoption of skb_attempt_defer_free() in UDP. The issue here is that skb_release_head_state() is called twice per skb, one time from skb_consume_udp(), then a second time from skb_defer_free_flush() and napi_consume_skb(). As Sabrina suggested, remove skb_release_head_state() call from skb_consume_udp(). Add a DEBUG_NET_WARN_ON_ONCE(skb_nfct(skb)) in skb_attempt_defer_free() Many thanks to Michal, Sabrina, Paolo and Florian for their help. Fixes: 6471658dc66c ("udp: use skb_attempt_defer_free()") Reported-and-bisected-by: Michal Kubecek Closes: https://lore.kernel.org/netdev/gpjh4lrotyephiqpuldtxxizrsg6job7cvhiqrw72saz2ubs3h@g6fgbvexgl3r/ Signed-off-by: Eric Dumazet Tested-by: Michal Kubecek Cc: Sabrina Dubroca Cc: Florian Westphal Reviewed-by: Sabrina Dubroca Link: https://patch.msgid.link/20251015052715.4140493-1-edumazet@google.com Signed-off-by: Paolo Abeni --- net/core/skbuff.c | 1 + net/ipv4/udp.c | 2 -- 2 files changed, 1 insertion(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index bc12790017b0..6be01454f262 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -7200,6 +7200,7 @@ nodefer: kfree_skb_napi_cache(skb); DEBUG_NET_WARN_ON_ONCE(skb_dst(skb)); DEBUG_NET_WARN_ON_ONCE(skb->destructor); + DEBUG_NET_WARN_ON_ONCE(skb_nfct(skb)); sdn = per_cpu_ptr(net_hotdata.skb_defer_nodes, cpu) + numa_node_id(); diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c index 95241093b7f0..30dfbf73729d 100644 --- a/net/ipv4/udp.c +++ b/net/ipv4/udp.c @@ -1851,8 +1851,6 @@ void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len) sk_peek_offset_bwd(sk, len); if (!skb_shared(skb)) { - if (unlikely(udp_skb_has_head_state(skb))) - skb_release_head_state(skb); skb_attempt_defer_free(skb); return; } -- 2.51.0