diff options
Diffstat (limited to 'Documentation/networking/netdevices.rst')
| -rw-r--r-- | Documentation/networking/netdevices.rst | 96 |
1 files changed, 83 insertions, 13 deletions
diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst index 1d37038e9fbe..eab601ab2db0 100644 --- a/Documentation/networking/netdevices.rst +++ b/Documentation/networking/netdevices.rst @@ -210,49 +210,55 @@ packets is preferred. struct net_device synchronization rules ======================================= ndo_open: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process ndo_stop: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process Note: netif_running() is guaranteed false ndo_do_ioctl: Synchronization: rtnl_lock() semaphore. - Context: process - This is only called by network subsystems internally, - not by user space calling ioctl as it was in before - linux-5.14. + This is only called by network subsystems internally, + not by user space calling ioctl as it was in before + linux-5.14. ndo_siocbond: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process - Used by the bonding driver for the SIOCBOND family of - ioctl commands. + Used by the bonding driver for the SIOCBOND family of + ioctl commands. ndo_siocwandev: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process Used by the drivers/net/wan framework to handle the SIOCWANDEV ioctl with the if_settings structure. ndo_siocdevprivate: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process This is used to implement SIOCDEVPRIVATE ioctl helpers. These should not be added to new drivers, so don't use. ndo_eth_ioctl: - Synchronization: rtnl_lock() semaphore. + Synchronization: rtnl_lock() semaphore. In addition, netdev instance + lock if the driver implements queue management or shaper API. Context: process ndo_get_stats: - Synchronization: rtnl_lock() semaphore, or RCU. + Synchronization: RCU (can be called concurrently with the stats + update path). Context: atomic (can't sleep under RCU) ndo_start_xmit: @@ -284,6 +290,16 @@ ndo_set_rx_mode: Synchronization: netif_addr_lock spinlock. Context: BHs disabled +ndo_setup_tc: + ``TC_SETUP_BLOCK`` and ``TC_SETUP_FT`` are running under NFT locks + (i.e. no ``rtnl_lock`` and no device instance lock). The rest of + ``tc_setup_type`` types run under netdev instance lock if the driver + implements queue management or shaper API. + +Most ndo callbacks not specified in the list above are running +under ``rtnl_lock``. In addition, netdev instance lock is taken as well if +the driver implements queue management or shaper API. + struct napi_struct synchronization rules ======================================== napi->poll: @@ -298,6 +314,60 @@ napi->poll: 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 +============================= + +Historically, all networking control operations were protected by a single +global lock known as ``rtnl_lock``. There is an ongoing effort to replace this +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 +drivers to opt out of using ``rtnl_lock`` and instead perform their control +operations directly under the netdev instance lock. + +Devices drivers are encouraged to rely on the instance lock where possible. + +For the (mostly software) drivers that need to interact with the core stack, +there are two sets of interfaces: ``dev_xxx``/``netdev_xxx`` and ``netif_xxx`` +(e.g., ``dev_set_mtu`` and ``netif_set_mtu``). The ``dev_xxx``/``netdev_xxx`` +functions handle acquiring the instance lock themselves, while the +``netif_xxx`` functions assume that the driver has already acquired +the instance lock. + +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 +instance lock. + +For devices with locked ops, currently only the following notifiers are +running under the lock: +* ``NETDEV_REGISTER`` +* ``NETDEV_UP`` +* ``NETDEV_CHANGE`` + +The following notifiers are running without the lock: +* ``NETDEV_UNREGISTER`` + +There are no clear expectations for the remaining notifiers. Notifiers not on +the list may run with or without the instance lock, potentially even invoking +the same notifier type with and without the lock from different code paths. +The goal is to eventually ensure that all (or most, with a few documented +exceptions) notifiers run under the instance lock. Please extend this +documentation whenever you make explicit assumption about lock being held +from a notifier. + NETDEV_INTERNAL symbol namespace ================================ |