netdev - Re: [PATCH v3 net] udp: do not use skb_release_head_state() before skb_attempt_defer

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Message-ID: <aO_-R4TlViHk_HB7@krikkit>
Date: Wed, 15 Oct 2025 22:04:23 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org,
	eric.dumazet@...il.com, Michal Kubecek <mkubecek@...e.cz>,
	Florian Westphal <fw@...len.de>
Subject: Re: [PATCH v3 net] udp: do not use skb_release_head_state() before
 skb_attempt_defer_free()

2025-10-15, 05:27:15 +0000, Eric Dumazet wrote:
> 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 <mkubecek@...e.cz>
> Closes: https://lore.kernel.org/netdev/gpjh4lrotyephiqpuldtxxizrsg6job7cvhiqrw72saz2ubs3h@g6fgbvexgl3r/
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Tested-by: Michal Kubecek <mkubecek@...e.cz>
> Cc: Sabrina Dubroca <sd@...asysnail.net>
> Cc: Florian Westphal <fw@...len.de>

Reviewed-by: Sabrina Dubroca <sd@...asysnail.net>

Thanks Eric.

-- 
Sabrina