Re: [PATCH] udp: Add noinline_for_tracing annotation for udp{,_v6}_send_skb()

[Kuniyuki Iwashima]

On Mon, 19 Oct 2026 23:07:58 +0000, Josh Don wrote:
> We hook udp_send_skb() and udp_v6_send_skb() using BPF fentry programs
> to monitor UDP transmits. Both functions are static and have two
> callers: udp{,v6}_sendmsg() and udp{,_v6}_push_pending_frames().
> 
> After an FDO profile update, udp_v6_send_skb() is now inlined into
> udpv6_sendmsg(), while an out-of-line copy remains for
> udp_v6_push_pending_frames(). The fentry program still attaches
> successfully, but it is silently bypassed for all uncorked sends.
> 
> To address this, make both functions noinline explicitly for tracing,
> as was done for tcp_drop_reason() in commit dbd5e2e79ed8 ("net: tcp:
> Add noinline_for_tracing annotation for tcp_drop_reason()").

Unlike tcp_drop_reason(), udp_send_skb() is a hot function as
inlined by FDO.

Did you see how this change affects to udp_rr performance ?

Also, net-next is closed.
https://lore.kernel.org/netdev/7a0446eb-8539-4300-ae0b-a3d66a692cbc@xxxxxxxxxx/


> 
> Assisted-by: LLM
> Signed-off-by: Josh Don <joshdon@xxxxxxxxxx>
> ---
>  net/ipv4/udp.c | 4 ++--
>  net/ipv6/udp.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index b090bd1f59e86..487c8cc8ab206 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -1110,8 +1110,8 @@ void udp_set_csum(bool nocheck, struct sk_buff *skb,
>  }
>  EXPORT_SYMBOL(udp_set_csum);
>  
> -static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
> -			struct inet_cork *cork)
> +noinline_for_tracing static int
> +udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4, struct inet_cork *cork)
>  {
>  	struct sock *sk = skb->sk;
>  	int offset, len, datalen;
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index 93478d1ad5769..fe92538835176 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -1366,8 +1366,8 @@ static void udp6_hwcsum_outgoing(struct sock *sk, struct sk_buff *skb,
>   *	Sending
>   */
>  
> -static int udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6,
> -			   struct inet_cork *cork)
> +noinline_for_tracing static int
> +udp_v6_send_skb(struct sk_buff *skb, struct flowi6 *fl6, struct inet_cork *cork)
>  {
>  	struct sock *sk = skb->sk;
>  	int offset, len, datalen;
> -- 
> 2.56.0.212.g129ede20d9-goog
>