netdev - Re: [PATCH net-next v3 03/10] net: sched: refactor block offloads counter usage

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Date:   Mon, 26 Aug 2019 17:46:34 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Vlad Buslov <vladbu@...lanox.com>
Cc:     netdev@...r.kernel.org, jhs@...atatu.com, xiyou.wangcong@...il.com,
        davem@...emloft.net, jakub.kicinski@...ronome.com,
        pablo@...filter.org
Subject: Re: [PATCH net-next v3 03/10] net: sched: refactor block offloads
 counter usage

Mon, Aug 26, 2019 at 03:44:59PM CEST, vladbu@...lanox.com wrote:
>Without rtnl lock protection filters can no longer safely manage block
>offloads counter themselves. Refactor cls API to protect block offloadcnt
>with tcf_block->cb_lock that is already used to protect driver callback
>list and nooffloaddevcnt counter. The counter can be modified by concurrent
>tasks by new functions that execute block callbacks (which is safe with
>previous patch that changed its type to atomic_t), however, block
>bind/unbind code that checks the counter value takes cb_lock in write mode
>to exclude any concurrent modifications. This approach prevents race
>conditions between bind/unbind and callback execution code but allows for
>concurrency for tc rule update path.
>
>Move block offload counter, filter in hardware counter and filter flags
>management from classifiers into cls hardware offloads API. Make functions
>tcf_block_offload_{inc|dec}() and tc_cls_offload_cnt_update() to be cls API
>private. Implement following new cls API to be used instead:
>
>  tc_setup_cb_add() - non-destructive filter add. If filter that wasn't
>  already in hardware is successfully offloaded, increment block offloads
>  counter, set filter in hardware counter and flag. On failure, previously
>  offloaded filter is considered to be intact and offloads counter is not
>  decremented.
>
>  tc_setup_cb_replace() - destructive filter replace. Release existing
>  filter block offload counter and reset its in hardware counter and flag.
>  Set new filter in hardware counter and flag. On failure, previously
>  offloaded filter is considered to be destroyed and offload counter is
>  decremented.
>
>  tc_setup_cb_destroy() - filter destroy. Unconditionally decrement block
>  offloads counter.
>
>  tc_setup_cb_reoffload() - reoffload filter to single cb. Execute cb() and
>  call tc_cls_offload_cnt_update() if cb() didn't return an error.
>
>Refactor all offload-capable classifiers to atomically offload filters to
>hardware, change block offload counter, and set filter in hardware counter
>and flag by means of the new cls API functions.
>
>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>

Acked-by: Jiri Pirko <jiri@...lanox.com>