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kernel: ksmbd: avoid busy polling

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Backport a patch to use blocking kernel_accept() and a fix for it,
avoiding busy polling.

Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/24987
Signed-off-by: Robert Marko <robimarko@gmail.com>
This commit is contained in:
Qingfang Deng
2026-09-07 09:55:05 +02:00
committed by Robert Marko
parent e1f69d04e0
commit dc4c215080
8 changed files with 470 additions and 8 deletions
Download Patch File Download Diff File Expand all files Collapse all files
target/linux/generic/backport-6.12/501-v6.19-ksmbd-server-avoid-busy-polling-in-accept-loop.patch
+130
View File
@@ -0,0 +1,130 @@
From 3316a8fc840d82fad5efcf76ad0ea3f76fdca209 Mon Sep 17 00:00:00 2001
From: Qingfang Deng <dqfext@gmail.com>
Date: Mon, 17 Nov 2025 16:59:00 +0800
Subject: [PATCH] ksmbd: server: avoid busy polling in accept loop
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. During teardown, call shutdown() on the listening socket so that
accept() returns -EINVAL and the thread exits cleanly.
The socket release mutex is redundant because kthread_stop() blocks until
the listener thread returns, guaranteeing safe teardown ordering.
Also remove sk_rcvtimeo and sk_sndtimeo assignments, which only caused
accept() to return -EAGAIN prematurely.
Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
fs/smb/server/transport_tcp.c | 41 +++++------------------------------
1 file changed, 6 insertions(+), 35 deletions(-)
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -22,7 +22,6 @@ struct interface {
struct socket *ksmbd_socket;
struct list_head entry;
char *name;
- struct mutex sock_release_lock;
int state;
};
@@ -57,21 +56,6 @@ static inline void ksmbd_tcp_reuseaddr(s
sock_set_reuseaddr(sock->sk);
}
-static inline void ksmbd_tcp_rcv_timeout(struct socket *sock, s64 secs)
-{
- lock_sock(sock->sk);
- if (secs && secs < MAX_SCHEDULE_TIMEOUT / HZ - 1)
- sock->sk->sk_rcvtimeo = secs * HZ;
- else
- sock->sk->sk_rcvtimeo = MAX_SCHEDULE_TIMEOUT;
- release_sock(sock->sk);
-}
-
-static inline void ksmbd_tcp_snd_timeout(struct socket *sock, s64 secs)
-{
- sock_set_sndtimeo(sock->sk, secs);
-}
-
static struct tcp_transport *alloc_transport(struct socket *client_sk)
{
struct tcp_transport *t;
@@ -254,20 +238,14 @@ static int ksmbd_kthread_fn(void *p)
unsigned int max_ip_conns;
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,
- SOCK_NONBLOCK);
- mutex_unlock(&iface->sock_release_lock);
- if (ret) {
- if (ret == -EAGAIN)
- /* check for new connections every 100 msecs */
- schedule_timeout_interruptible(HZ / 10);
+ ret = kernel_accept(iface->ksmbd_socket, &client_sk, 0);
+ if (ret == -EINVAL)
+ break;
+ if (ret)
continue;
- }
if (!server_conf.max_ip_connections)
goto skip_max_ip_conns_limit;
@@ -474,10 +452,6 @@ static void tcp_destroy_socket(struct so
if (!ksmbd_socket)
return;
- /* set zero to timeout */
- ksmbd_tcp_rcv_timeout(ksmbd_socket, 0);
- ksmbd_tcp_snd_timeout(ksmbd_socket, 0);
-
ret = kernel_sock_shutdown(ksmbd_socket, SHUT_RDWR);
if (ret)
pr_err("Failed to shutdown socket: %d\n", ret);
@@ -548,9 +522,6 @@ static int create_socket(struct interfac
goto out_error;
}
- ksmbd_socket->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
- ksmbd_socket->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
-
ret = kernel_listen(ksmbd_socket, KSMBD_SOCKET_BACKLOG);
if (ret) {
pr_err("Port listen() error: %d\n", ret);
@@ -620,12 +591,11 @@ static int ksmbd_netdev_event(struct not
if (iface && iface->state == IFACE_STATE_CONFIGURED) {
ksmbd_debug(CONN, "netdev-down event: netdev(%s) is going down\n",
iface->name);
+ kernel_sock_shutdown(iface->ksmbd_socket, SHUT_RDWR);
tcp_stop_kthread(iface->ksmbd_kthread);
iface->ksmbd_kthread = NULL;
- mutex_lock(&iface->sock_release_lock);
- tcp_destroy_socket(iface->ksmbd_socket);
+ sock_release(iface->ksmbd_socket);
iface->ksmbd_socket = NULL;
- mutex_unlock(&iface->sock_release_lock);
iface->state = IFACE_STATE_DOWN;
break;
@@ -688,7 +658,6 @@ static struct interface *alloc_iface(cha
iface->name = ifname;
iface->state = IFACE_STATE_DOWN;
list_add(&iface->entry, &iface_list);
- mutex_init(&iface->sock_release_lock);
return iface;
}
target/linux/generic/backport-6.12/503-01-v7.3-ksmbd-enable-tcp-keepalive-for-accepted-connections.patch
+1 -1
View File
@@ -20,7 +20,7 @@ Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -325,6 +325,12 @@ skip_max_ip_conns_limit:
@@ -303,6 +303,12 @@ skip_max_ip_conns_limit:
ksmbd_debug(CONN, "connect success: accepted new connection\n");
client_sk->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
client_sk->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
target/linux/generic/backport-6.12/503-02-v7.3-ksmbd-keep-tcp-timers-alive-for-kernel-sockets.patch
+3 -3
View File
@@ -27,9 +27,9 @@ Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -557,6 +557,12 @@ static int create_socket(struct interfac
ksmbd_socket->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
ksmbd_socket->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
@@ -528,6 +528,12 @@ static int create_socket(struct interfac
goto out_error;
}
+ /*
+ * Accepted sockets inherit the listener's net reference. Keep TCP
target/linux/generic/backport-6.12/504-v7.3-ksmbd-fix-listener-task-lifetime-on-netdev-events.patch
+102
View File
@@ -0,0 +1,102 @@
From a506290f59e1c6ce9ac0a13158640bb8fee93471 Mon Sep 17 00:00:00 2001
From: Namjae Jeon <linkinjeon@kernel.org>
Date: Fri, 28 Aug 2026 09:24:49 +0900
Subject: [PATCH] ksmbd: fix listener task lifetime on netdev events
The listener thread exits when its listening socket is shutdown. The
netdevice notifier shuts down the socket before calling kthread_stop(), so
the task_struct can be freed before kthread_stop() gets its reference.
Create the listener in a stopped state and hold an extra task_struct
reference until kthread_stop_put() completes. Also stop and release
listeners before freeing their interface records during TCP teardown.
Fixes: 3316a8fc840d ("ksmbd: server: avoid busy polling in accept loop")
Reported-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
fs/smb/server/transport_tcp.c | 36 ++++++++++++++++++++++++++---------
1 file changed, 27 insertions(+), 9 deletions(-)
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -39,6 +39,7 @@ struct tcp_transport {
static const struct ksmbd_transport_ops ksmbd_tcp_transport_ops;
static void tcp_stop_kthread(struct task_struct *kthread);
+static void ksmbd_tcp_stop_listener(struct interface *iface);
static struct interface *alloc_iface(char *ifname);
static void ksmbd_tcp_disconnect(struct ksmbd_transport *t);
@@ -332,13 +333,20 @@ static int ksmbd_tcp_run_kthread(struct
int rc;
struct task_struct *kthread;
- kthread = kthread_run(ksmbd_kthread_fn, (void *)iface, "ksmbd-%s",
- iface->name);
+ kthread = kthread_create(ksmbd_kthread_fn, (void *)iface, "ksmbd-%s",
+ iface->name);
if (IS_ERR(kthread)) {
rc = PTR_ERR(kthread);
return rc;
}
+
+ /*
+ * The listener can exit after its socket is shutdown, so keep the
+ * task_struct alive until the caller has stopped it.
+ */
+ get_task_struct(kthread);
iface->ksmbd_kthread = kthread;
+ wake_up_process(kthread);
return 0;
}
@@ -603,12 +611,7 @@ static int ksmbd_netdev_event(struct not
if (iface && iface->state == IFACE_STATE_CONFIGURED) {
ksmbd_debug(CONN, "netdev-down event: netdev(%s) is going down\n",
iface->name);
- kernel_sock_shutdown(iface->ksmbd_socket, SHUT_RDWR);
- tcp_stop_kthread(iface->ksmbd_kthread);
- iface->ksmbd_kthread = NULL;
- sock_release(iface->ksmbd_socket);
- iface->ksmbd_socket = NULL;
-
+ ksmbd_tcp_stop_listener(iface);
iface->state = IFACE_STATE_DOWN;
break;
}
@@ -636,11 +639,25 @@ static void tcp_stop_kthread(struct task
if (!kthread)
return;
- ret = kthread_stop(kthread);
+ ret = kthread_stop_put(kthread);
if (ret)
pr_err("failed to stop forker thread\n");
}
+static void ksmbd_tcp_stop_listener(struct interface *iface)
+{
+ if (iface->ksmbd_socket)
+ kernel_sock_shutdown(iface->ksmbd_socket, SHUT_RDWR);
+
+ tcp_stop_kthread(iface->ksmbd_kthread);
+ iface->ksmbd_kthread = NULL;
+
+ if (iface->ksmbd_socket) {
+ sock_release(iface->ksmbd_socket);
+ iface->ksmbd_socket = NULL;
+ }
+}
+
void ksmbd_tcp_destroy(void)
{
struct interface *iface, *tmp;
@@ -648,6 +665,7 @@ void ksmbd_tcp_destroy(void)
unregister_netdevice_notifier(&ksmbd_netdev_notifier);
list_for_each_entry_safe(iface, tmp, &iface_list, entry) {
+ ksmbd_tcp_stop_listener(iface);
list_del(&iface->entry);
kfree(iface->name);
kfree(iface);
target/linux/generic/backport-6.18/500-v6.19-ksmbd-server-avoid-busy-polling-in-accept-loop.patch
+128
View File
@@ -0,0 +1,128 @@
From 3316a8fc840d82fad5efcf76ad0ea3f76fdca209 Mon Sep 17 00:00:00 2001
From: Qingfang Deng <dqfext@gmail.com>
Date: Mon, 17 Nov 2025 16:59:00 +0800
Subject: [PATCH] ksmbd: server: avoid busy polling in accept loop
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. During teardown, call shutdown() on the listening socket so that
accept() returns -EINVAL and the thread exits cleanly.
The socket release mutex is redundant because kthread_stop() blocks until
the listener thread returns, guaranteeing safe teardown ordering.
Also remove sk_rcvtimeo and sk_sndtimeo assignments, which only caused
accept() to return -EAGAIN prematurely.
Signed-off-by: Qingfang Deng <dqfext@gmail.com>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
fs/smb/server/transport_tcp.c | 41 +++++------------------------------
1 file changed, 6 insertions(+), 35 deletions(-)
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -22,7 +22,6 @@ struct interface {
struct socket *ksmbd_socket;
struct list_head entry;
char *name;
- struct mutex sock_release_lock;
int state;
};
@@ -57,19 +56,6 @@ static inline void ksmbd_tcp_reuseaddr(s
sock_set_reuseaddr(sock->sk);
}
-static inline void ksmbd_tcp_rcv_timeout(struct socket *sock, s64 secs)
-{
- if (secs && secs < MAX_SCHEDULE_TIMEOUT / HZ - 1)
- WRITE_ONCE(sock->sk->sk_rcvtimeo, secs * HZ);
- else
- WRITE_ONCE(sock->sk->sk_rcvtimeo, MAX_SCHEDULE_TIMEOUT);
-}
-
-static inline void ksmbd_tcp_snd_timeout(struct socket *sock, s64 secs)
-{
- sock_set_sndtimeo(sock->sk, secs);
-}
-
static struct tcp_transport *alloc_transport(struct socket *client_sk)
{
struct tcp_transport *t;
@@ -239,20 +225,14 @@ static int ksmbd_kthread_fn(void *p)
unsigned int max_ip_conns;
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,
- SOCK_NONBLOCK);
- mutex_unlock(&iface->sock_release_lock);
- if (ret) {
- if (ret == -EAGAIN)
- /* check for new connections every 100 msecs */
- schedule_timeout_interruptible(HZ / 10);
+ ret = kernel_accept(iface->ksmbd_socket, &client_sk, 0);
+ if (ret == -EINVAL)
+ break;
+ if (ret)
continue;
- }
if (!server_conf.max_ip_connections)
goto skip_max_ip_conns_limit;
@@ -461,10 +441,6 @@ static void tcp_destroy_socket(struct so
if (!ksmbd_socket)
return;
- /* set zero to timeout */
- ksmbd_tcp_rcv_timeout(ksmbd_socket, 0);
- ksmbd_tcp_snd_timeout(ksmbd_socket, 0);
-
ret = kernel_sock_shutdown(ksmbd_socket, SHUT_RDWR);
if (ret)
pr_err("Failed to shutdown socket: %d\n", ret);
@@ -535,9 +511,6 @@ static int create_socket(struct interfac
goto out_error;
}
- ksmbd_socket->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
- ksmbd_socket->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
-
ret = kernel_listen(ksmbd_socket, KSMBD_SOCKET_BACKLOG);
if (ret) {
pr_err("Port listen() error: %d\n", ret);
@@ -607,12 +580,11 @@ static int ksmbd_netdev_event(struct not
if (iface && iface->state == IFACE_STATE_CONFIGURED) {
ksmbd_debug(CONN, "netdev-down event: netdev(%s) is going down\n",
iface->name);
+ kernel_sock_shutdown(iface->ksmbd_socket, SHUT_RDWR);
tcp_stop_kthread(iface->ksmbd_kthread);
iface->ksmbd_kthread = NULL;
- mutex_lock(&iface->sock_release_lock);
- tcp_destroy_socket(iface->ksmbd_socket);
+ sock_release(iface->ksmbd_socket);
iface->ksmbd_socket = NULL;
- mutex_unlock(&iface->sock_release_lock);
iface->state = IFACE_STATE_DOWN;
break;
@@ -675,7 +647,6 @@ static struct interface *alloc_iface(cha
iface->name = ifname;
iface->state = IFACE_STATE_DOWN;
list_add(&iface->entry, &iface_list);
- mutex_init(&iface->sock_release_lock);
return iface;
}
target/linux/generic/backport-6.18/503-01-v7.3-ksmbd-enable-tcp-keepalive-for-accepted-connections.patch
+1 -1
View File
@@ -20,7 +20,7 @@ Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -312,6 +312,12 @@ skip_max_ip_conns_limit:
@@ -292,6 +292,12 @@ skip_max_ip_conns_limit:
ksmbd_debug(CONN, "connect success: accepted new connection\n");
client_sk->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
client_sk->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
target/linux/generic/backport-6.18/503-02-v7.3-ksmbd-keep-tcp-timers-alive-for-kernel-sockets.patch
+3 -3
View File
@@ -27,9 +27,9 @@ Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -544,6 +544,12 @@ static int create_socket(struct interfac
ksmbd_socket->sk->sk_rcvtimeo = KSMBD_TCP_RECV_TIMEOUT;
ksmbd_socket->sk->sk_sndtimeo = KSMBD_TCP_SEND_TIMEOUT;
@@ -517,6 +517,12 @@ static int create_socket(struct interfac
goto out_error;
}
+ /*
+ * Accepted sockets inherit the listener's net reference. Keep TCP
target/linux/generic/backport-6.18/504-v7.3-ksmbd-fix-listener-task-lifetime-on-netdev-events.patch
+102
View File
@@ -0,0 +1,102 @@
From a506290f59e1c6ce9ac0a13158640bb8fee93471 Mon Sep 17 00:00:00 2001
From: Namjae Jeon <linkinjeon@kernel.org>
Date: Fri, 28 Aug 2026 09:24:49 +0900
Subject: [PATCH] ksmbd: fix listener task lifetime on netdev events
The listener thread exits when its listening socket is shutdown. The
netdevice notifier shuts down the socket before calling kthread_stop(), so
the task_struct can be freed before kthread_stop() gets its reference.
Create the listener in a stopped state and hold an extra task_struct
reference until kthread_stop_put() completes. Also stop and release
listeners before freeing their interface records during TCP teardown.
Fixes: 3316a8fc840d ("ksmbd: server: avoid busy polling in accept loop")
Reported-by: Farhad Alemi <farhad.alemi@berkeley.edu>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
---
fs/smb/server/transport_tcp.c | 36 ++++++++++++++++++++++++++---------
1 file changed, 27 insertions(+), 9 deletions(-)
--- a/fs/smb/server/transport_tcp.c
+++ b/fs/smb/server/transport_tcp.c
@@ -39,6 +39,7 @@ struct tcp_transport {
static const struct ksmbd_transport_ops ksmbd_tcp_transport_ops;
static void tcp_stop_kthread(struct task_struct *kthread);
+static void ksmbd_tcp_stop_listener(struct interface *iface);
static struct interface *alloc_iface(char *ifname);
static void ksmbd_tcp_disconnect(struct ksmbd_transport *t);
@@ -321,13 +322,20 @@ static int ksmbd_tcp_run_kthread(struct
int rc;
struct task_struct *kthread;
- kthread = kthread_run(ksmbd_kthread_fn, (void *)iface, "ksmbd-%s",
- iface->name);
+ kthread = kthread_create(ksmbd_kthread_fn, (void *)iface, "ksmbd-%s",
+ iface->name);
if (IS_ERR(kthread)) {
rc = PTR_ERR(kthread);
return rc;
}
+
+ /*
+ * The listener can exit after its socket is shutdown, so keep the
+ * task_struct alive until the caller has stopped it.
+ */
+ get_task_struct(kthread);
iface->ksmbd_kthread = kthread;
+ wake_up_process(kthread);
return 0;
}
@@ -592,12 +600,7 @@ static int ksmbd_netdev_event(struct not
if (iface && iface->state == IFACE_STATE_CONFIGURED) {
ksmbd_debug(CONN, "netdev-down event: netdev(%s) is going down\n",
iface->name);
- kernel_sock_shutdown(iface->ksmbd_socket, SHUT_RDWR);
- tcp_stop_kthread(iface->ksmbd_kthread);
- iface->ksmbd_kthread = NULL;
- sock_release(iface->ksmbd_socket);
- iface->ksmbd_socket = NULL;
-
+ ksmbd_tcp_stop_listener(iface);
iface->state = IFACE_STATE_DOWN;
break;
}
@@ -625,11 +628,25 @@ static void tcp_stop_kthread(struct task
if (!kthread)
return;
- ret = kthread_stop(kthread);
+ ret = kthread_stop_put(kthread);
if (ret)
pr_err("failed to stop forker thread\n");
}
+static void ksmbd_tcp_stop_listener(struct interface *iface)
+{
+ if (iface->ksmbd_socket)
+ kernel_sock_shutdown(iface->ksmbd_socket, SHUT_RDWR);
+
+ tcp_stop_kthread(iface->ksmbd_kthread);
+ iface->ksmbd_kthread = NULL;
+
+ if (iface->ksmbd_socket) {
+ sock_release(iface->ksmbd_socket);
+ iface->ksmbd_socket = NULL;
+ }
+}
+
void ksmbd_tcp_destroy(void)
{
struct interface *iface, *tmp;
@@ -637,6 +654,7 @@ void ksmbd_tcp_destroy(void)
unregister_netdevice_notifier(&ksmbd_netdev_notifier);
list_for_each_entry_safe(iface, tmp, &iface_list, entry) {
+ ksmbd_tcp_stop_listener(iface);
list_del(&iface->entry);
kfree(iface->name);
kfree(iface);