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

[Josh Don <joshdon@google.com>]

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()").

Assisted-by: LLM
Signed-off-by: Josh Don <joshdon@google.com>
---
 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