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 --- v3: Florian suggested skb_attempt_defer_free() as a better place for the DEBUG_NET_WARN_ON_ONCE(skb_nfct(skb)), since it already had the skb_dst(skb) and skb->destructor checks. v2: Adopted Sabrina suggestion. https://lore.kernel.org/netdev/20251014132917.2841932-1-edumazet@google.com/T/#u v1: https://lore.kernel.org/netdev/aO3_hBg5expKNv6v@krikkit/T/#m8a88669b801d85f57b73710cdb0c8ee63854af11 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 bc12790017b0b5c0be99f8fb9d362b3730fa4eb0..6be01454f262a2acbf3f5905498961d132442d2c 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 95241093b7f01b2dc31d9520b693f46400e545ff..30dfbf73729dad1e7b26c74a4791fe0a82682a6d 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; } -- 2.51.0.788.g6d19910ace-goog