netdev - [PATCH net] Revert "udp: avoid calling sock_def

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Message-ID: <20241202155620.1719-1-ffmancera@riseup.net>
Date: Mon,  2 Dec 2024 15:56:08 +0000
From: Fernando Fernandez Mancera <ffmancera@...eup.net>
To: netdev@...r.kernel.org
Cc: edumazet@...gle.com,
	pabeni@...hat.com,
	Fernando Fernandez Mancera <ffmancera@...eup.net>
Subject: [PATCH net] Revert "udp: avoid calling sock_def_readable() if possible"

This reverts commit 612b1c0dec5bc7367f90fc508448b8d0d7c05414. On a
scenario with multiple threads blocking on a recvfrom(), we need to call
sock_def_readable() on every __udp_enqueue_schedule_skb() otherwise the
threads won't be woken up as __skb_wait_for_more_packets() is using
prepare_to_wait_exclusive().

Link: https://bugzilla.redhat.com/2308477
Fixes: 612b1c0dec5b ("udp: avoid calling sock_def_readable() if possible")
Signed-off-by: Fernando Fernandez Mancera <ffmancera@...eup.net>
---
 net/ipv4/udp.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 6a01905d379f..e8953e88efef 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1674,7 +1674,6 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 	struct sk_buff_head *list = &sk->sk_receive_queue;
 	int rmem, err = -ENOMEM;
 	spinlock_t *busy = NULL;
-	bool becomes_readable;
 	int size, rcvbuf;
 
 	/* Immediately drop when the receive queue is full.
@@ -1715,19 +1714,12 @@ int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
 	 */
 	sock_skb_set_dropcount(sk, skb);
 
-	becomes_readable = skb_queue_empty(list);
 	__skb_queue_tail(list, skb);
 	spin_unlock(&list->lock);
 
-	if (!sock_flag(sk, SOCK_DEAD)) {
-		if (becomes_readable ||
-		    sk->sk_data_ready != sock_def_readable ||
-		    READ_ONCE(sk->sk_peek_off) >= 0)
-			INDIRECT_CALL_1(sk->sk_data_ready,
-					sock_def_readable, sk);
-		else
-			sk_wake_async_rcu(sk, SOCK_WAKE_WAITD, POLL_IN);
-	}
+	if (!sock_flag(sk, SOCK_DEAD))
+		INDIRECT_CALL_1(sk->sk_data_ready, sock_def_readable, sk);
+
 	busylock_release(busy);
 	return 0;
 
-- 
2.47.1