On Mon, 26 Aug 2019 16:44:56 +0300, Vlad Buslov wrote: > Currently, all cls API hardware offloads driver callbacks require caller > to hold rtnl lock when calling them. This patch set introduces new API > that allows drivers to register callbacks that are not dependent on rtnl > lock and unlocked classifiers to offload filters without obtaining rtnl > lock first, which is intended to allow offloading tc rules in parallel. > > Recently, new rtnl registration flag RTNL_FLAG_DOIT_UNLOCKED was added. > TC rule update handlers (RTM_NEWTFILTER, RTM_DELTFILTER, etc.) are > already registered with this flag and only take rtnl lock when qdisc or > classifier requires it. Classifiers can indicate that their ops > callbacks don't require caller to hold rtnl lock by setting the > TCF_PROTO_OPS_DOIT_UNLOCKED flag. Unlocked implementation of flower > classifier is now upstreamed. However, this implementation still obtains > rtnl lock before calling hardware offloads API. > > Implement following cls API changes: > > - Introduce new "unlocked_driver_cb" flag to struct flow_block_offload > to allow registering and unregistering block hardware offload > callbacks that do not require caller to hold rtnl lock. Drivers that > doesn't require users of its tc offload callbacks to hold rtnl lock > sets the flag to true on block bind/unbind. Internally tcf_block is > extended with additional lockeddevcnt counter that is used to count > number of devices that require rtnl lock that block is bound to. When > this counter is zero, tc_setup_cb_*() functions execute callbacks > without obtaining rtnl lock. > > - Extend cls API single hardware rule update tc_setup_cb_call() function > with tc_setup_cb_add(), tc_setup_cb_replace(), tc_setup_cb_destroy() > and tc_setup_cb_reoffload() functions. These new APIs are needed to > move management of block offload counter, filter in hardware counter > and flag from classifier implementations to cls API, which is now > responsible for managing them in concurrency-safe manner. Access to > cb_list from callback execution code is synchronized by obtaining new > 'cb_lock' rw_semaphore in read mode, which allows executing callbacks > in parallel, but excludes any modifications of data from > register/unregister code. tcf_block offloads counter type is changed > to atomic integer to allow updating the counter concurrently. > > - Extend classifier ops with new ops->hw_add() and ops->hw_del() > callbacks which are used to notify unlocked classifiers when filter is > successfully added or deleted to hardware without releasing cb_lock. > This is necessary to update classifier state atomically with callback > list traversal and updating of all relevant counters and allows > unlocked classifiers to synchronize with concurrent reoffload without > requiring any changes to driver callback API implementations. > > New tc flow_action infrastructure is also modified to allow its user to > execute without rtnl lock protection. Function tc_setup_flow_action() is > modified to conditionally obtain rtnl lock before accessing action > state. Action data that is accessed by reference is either copied or > reference counted to prevent concurrent action overwrite from > deallocating it. New function tc_cleanup_flow_action() is introduced to > cleanup/release all such data obtained by tc_setup_flow_action(). > > Flower classifier (only unlocked classifier at the moment) is modified > to use new cls hardware offloads API and no longer obtains rtnl lock > before calling it.
Acked-by: Jakub Kicinski <jakub.kicin...@netronome.com>
