From: Stefan Metzmacher <metze@samba.org>
To: Qingfang Deng <dqfext@gmail.com>,
Namjae Jeon <linkinjeon@kernel.org>,
Steve French <smfrench@gmail.com>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Tom Talpey <tom@talpey.com>,
Ronnie Sahlberg <lsahlber@redhat.com>,
Hyunchul Lee <hyc.lee@gmail.com>,
linux-cifs@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH] ksmbd: server: avoid busy polling in accept loop
Date: Tue, 11 Nov 2025 08:16:29 +0100 [thread overview]
Message-ID: <10da0cb9-8c92-413d-b8df-049279100458@samba.org> (raw)
In-Reply-To: <2516ed5d-fed2-47a3-b1eb-656d79d242f3@samba.org>
Am 11.11.25 um 07:55 schrieb Stefan Metzmacher:
> Am 30.10.25 um 07:47 schrieb Qingfang Deng:
>> The ksmbd listener thread was using busy waiting on a listening socket by
>> calling kernel_accept() with SOCK_NONBLOCK and retrying every 100ms on
>> -EAGAIN. Since this thread is dedicated to accepting new connections,
>> there is no need for non-blocking mode.
>>
>> Switch to a blocking accept() call instead, allowing the thread to sleep
>> until a new connection arrives. This avoids unnecessary wakeups and CPU
>> usage.
>>
>> Also remove:
>> - TCP_NODELAY, which has no effect on a listening socket.
>> - sk_rcvtimeo and sk_sndtimeo assignments, which only caused accept()
>> to return -EAGAIN prematurely.
>
> Aren't these inherited to the accepted sockets?
> So we need to apply them to the accepted sockets now
> instead of dropping them completely?
Actually the timeouts are added to the client connection,
but not the TCP_NODELAY.
But looking at it more detailed I'm wondering if this might
introduce a deadlock.
We have this in the accepting thread:
while (!kthread_should_stop()) {
mutex_lock(&iface->sock_release_lock);
if (!iface->ksmbd_socket) {
mutex_unlock(&iface->sock_release_lock);
break;
}
ret = kernel_accept(iface->ksmbd_socket, &client_sk, 0);
mutex_unlock(&iface->sock_release_lock);
if (ret)
continue;
And in the stopping code this:
case NETDEV_DOWN:
iface = ksmbd_find_netdev_name_iface_list(netdev->name);
if (iface && iface->state == IFACE_STATE_CONFIGURED) {
ksmbd_debug(CONN, "netdev-down event: netdev(%s) is going down\n",
iface->name);
tcp_stop_kthread(iface->ksmbd_kthread);
iface->ksmbd_kthread = NULL;
mutex_lock(&iface->sock_release_lock);
tcp_destroy_socket(iface->ksmbd_socket);
iface->ksmbd_socket = NULL;
mutex_unlock(&iface->sock_release_lock);
iface->state = IFACE_STATE_DOWN;
break;
}
I guess that now kernel_accept() call waits forever holding iface->sock_release_lock
and tcp_stop_kthread(iface->ksmbd_kthread); doesn't have any impact anymore
as we may never reach kthread_should_stop() anymore.
We may want to do a kernel_sock_shutdown(ksmbd_socket, SHUT_RDWR) after
tcp_stop_kthread(iface->ksmbd_kthread); but before mutex_lock(&iface->sock_release_lock);
so that kernel_accept() hopefully returns directly.
And we only call sock_release(ksmbd_socket); under the iface->sock_release_lock mutex.
metze
next prev parent reply other threads:[~2025-11-11 7:16 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-30 6:47 [PATCH] ksmbd: server: avoid busy polling in accept loop Qingfang Deng
2025-10-30 8:11 ` Namjae Jeon
2025-10-31 7:32 ` Qingfang Deng
2025-10-31 7:44 ` Greg Kroah-Hartman
2025-10-31 7:49 ` Qingfang Deng
2025-10-31 23:50 ` Namjae Jeon
2025-11-11 6:55 ` Stefan Metzmacher
2025-11-11 7:16 ` Stefan Metzmacher [this message]
2025-11-11 8:03 ` Qingfang Deng
2025-11-11 8:47 ` Namjae Jeon
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