netdev - [PATCH] sctp: Do not wake readers in __sctp_write

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Message-Id: <20250516081727.1361451-1-oss@malat.biz>
Date: Fri, 16 May 2025 10:17:28 +0200
From: Petr Malat <oss@...at.biz>
To: linux-sctp@...r.kernel.org
Cc: netdev@...r.kernel.org,
	marcelo.leitner@...il.com,
	Petr Malat <oss@...at.biz>,
	Xin Long <lucien.xin@...il.com>
Subject: [PATCH] sctp: Do not wake readers in __sctp_write_space()

Function __sctp_write_space() doesn't set poll key, which leads to
ep_poll_callback() waking up all waiters, not only these waiting
for the socket being writable. Set the key properly using
wake_up_interruptible_poll(), which is preferred over the sync
variant, as writers are not woken up before at least half of the
queue is available. Also, TCP does the same.

Signed-off-by: Petr Malat <oss@...at.biz>
Acked-by: Xin Long <lucien.xin@...il.com>
---
 net/sctp/socket.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 53725ee7ba06..b301d64d9d80 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -9100,7 +9100,8 @@ static void __sctp_write_space(struct sctp_association *asoc)
 		wq = rcu_dereference(sk->sk_wq);
 		if (wq) {
 			if (waitqueue_active(&wq->wait))
-				wake_up_interruptible(&wq->wait);
+				wake_up_interruptible_poll(&wq->wait, EPOLLOUT |
+						EPOLLWRNORM | EPOLLWRBAND);
 
 			/* Note that we try to include the Async I/O support
 			 * here by modeling from the current TCP/UDP code.
-- 
2.39.5