sctp: Do not wake readers in __sctp_write_space()

JIRA: https://issues.redhat.com/browse/RHEL-115641
Tested: compile only

commit af29589
Author: Petr Malat <oss@malat.biz>
Date:   Fri May 16 10:17:28 2025 +0200

    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@malat.biz>
    Acked-by: Xin Long <lucien.xin@gmail.com>
    Link: https://patch.msgid.link/20250516081727.1361451-1-oss@malat.biz
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Xin Long <lxin@redhat.com>

Author: Xin Long

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.