[PATCH net-next 7/8] docs: netdev: break down the instance locking info per ops struct

Jakub Kicinski
2025-04-07T19:01:21Z

Explicitly list all the ops structs and what locking they provide.
Use "ops locked" as a term for drivers which have ops called under
the instance lock.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
Documentation/networking/netdevices.rst | 54 +++++++++++++++++++------
1 file changed, 42 insertions(+), 12 deletions(-)

diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst
index d6357472d3f1..0cfff56b436e 100644
--- a/Documentation/networking/netdevices.rst
+++ b/Documentation/networking/netdevices.rst
@@ -314,13 +314,8 @@ struct napi_struct synchronization rules
softirq
will be called with interrupts disabled by netconsole.

-struct netdev_queue_mgmt_ops synchronization rules
-==================================================
-
-All queue management ndo callbacks are holding netdev instance lock.
-
-RTNL and netdev instance lock
-=============================
+netdev instance lock
+====================

Historically, all networking control operations were protected by a single
global lock known as ``rtnl_lock``. There is an ongoing effort to replace this
@@ -328,10 +323,13 @@ global lock with separate locks for each network namespace. Additionally,
properties of individual netdev are increasingly protected by per-netdev locks.

For device drivers that implement shaping or queue management APIs, all control
-operations will be performed under the netdev instance lock. Currently, this
-instance lock is acquired within the context of ``rtnl_lock``. The drivers
-can also explicitly request instance lock to be acquired via
-``request_ops_lock``. In the future, there will be an option for individual
+operations will be performed under the netdev instance lock.
+Drivers can also explicitly request instance lock to be held during ops
+by setting ``request_ops_lock`` to true. Code comments and docs refer
+to drivers which have ops called under the instance lock as "ops locked".
+See also the documentation of the ``lock`` member of struct net_device.
+
+In the future, there will be an option for individual
drivers to opt out of using ``rtnl_lock`` and instead perform their control
operations directly under the netdev instance lock.

@@ -343,8 +341,40 @@ there are two sets of interfaces: ``dev_xxx`` and ``netif_xxx`` (e.g.,
acquiring the instance lock themselves, while the ``netif_xxx`` functions
assume that the driver has already acquired the instance lock.

+struct net_device_ops
+---------------------
+
+``ndos`` are called without holding the instance lock for most drivers.
+
+"Ops locked" drivers will have most of the ``ndos`` invoked under
+the instance lock.
+
+struct ethtool_ops
+------------------
+
+Similarly to ``ndos`` the instance lock is only held for select drivers.
+For "ops locked" drivers all ethtool ops without an exception should
+be called under the instance lock.
+
+struct net_shaper_ops
+---------------------
+
+All net shaper callbacks are invoked while holding the netdev instance
+lock. ``rtnl_lock`` may or may not be held.
+
+Note that supporting net shapers automatically enables "ops locking".
+
+struct netdev_queue_mgmt_ops
+----------------------------
+
+All queue management callbacks are invoked while holding the netdev instance
+lock. ``rtnl_lock`` may or may not be held.
+
+Note that supporting struct netdev_queue_mgmt_ops automatically enables
+"ops locking".
+
Notifiers and netdev instance lock
-==================================
+----------------------------------

For device drivers that implement shaping or queue management APIs,
some of the notifiers (``enum netdev_cmd``) are running under the netdev
--
2.49.0