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From: Vlad Buslov <vladbu@mellanox.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Linux Kernel Network Developers <netdev@vger.kernel.org>,
	Jamal Hadi Salim <jhs@mojatatu.com>,
	Jiri Pirko <jiri@resnulli.us>, David Miller <davem@davemloft.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH net-next v4 05/17] net: sched: traverse chains in block with tcf_get_next_chain()
Date: Mon, 18 Feb 2019 10:07:04 +0000	[thread overview]
Message-ID: <vbflg2dqukb.fsf@mellanox.com> (raw)
In-Reply-To: <CAM_iQpUnmKPh+RCi-JyouKz7PrAiWPp30Ro2qZFrR=MjVHogHA@mail.gmail.com>

Hi Cong,

Thanks for reviewing!

On Fri 15 Feb 2019 at 22:21, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> (Sorry for joining this late.)
>
> On Mon, Feb 11, 2019 at 12:56 AM Vlad Buslov <vladbu@mellanox.com> wrote:
>> @@ -2432,7 +2474,11 @@ static int tc_dump_chain(struct sk_buff *skb, struct netlink_callback *cb)
>>         index_start = cb->args[0];
>>         index = 0;
>>
>> -       list_for_each_entry(chain, &block->chain_list, list) {
>> +       for (chain = __tcf_get_next_chain(block, NULL);
>> +            chain;
>> +            chain_prev = chain,
>> +                    chain = __tcf_get_next_chain(block, chain),
>> +                    tcf_chain_put(chain_prev)) {
>
> Why do you want to take the block->lock in each iteration
> of the loop rather than taking once for the whole loop?

This loop calls classifier ops callback in tc_chain_fill_node(). I don't
call any classifier ops callbacks while holding block or chain lock in
this change because the goal is to achieve fine-grained locking for data
structures used by filter update path. Locking per-block or per-chain is
much coarser than taking reference counters to parent structures and
allowing classifiers to implement their own locking.

In this case call to ops->tmplt_dump() is probably quite fast and its
execution time doesn't depend on number of filters on the classifier, so
releasing block->lock on each iteration doesn't provide much benefit, if
at all. However, it is easier for me to reason about locking correctness
in this refactoring by following a simple rule that no locks (besides
rtnl mutex) can be held when calling classifier ops callbacks.

  reply	other threads:[~2019-02-18 10:07 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11  8:55 [PATCH net-next v4 00/17] Refactor classifier API to work with chain/classifiers without rtnl lock Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 01/17] net: sched: protect block state with mutex Vlad Buslov
2019-02-11 14:15   ` Jiri Pirko
2019-02-11  8:55 ` [PATCH net-next v4 02/17] net: sched: protect chain->explicitly_created with block->lock Vlad Buslov
2019-02-11 14:15   ` Jiri Pirko
2019-02-11  8:55 ` [PATCH net-next v4 03/17] net: sched: refactor tc_ctl_chain() to use block->lock Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 04/17] net: sched: protect block->chain0 with block->lock Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 05/17] net: sched: traverse chains in block with tcf_get_next_chain() Vlad Buslov
2019-02-15 22:21   ` Cong Wang
2019-02-18 10:07     ` Vlad Buslov [this message]
2019-02-18 18:26       ` Cong Wang
2019-02-19 16:04         ` Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 06/17] net: sched: protect chain template accesses with block lock Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 07/17] net: sched: protect filter_chain list with filter_chain_lock mutex Vlad Buslov
2019-02-14 18:24   ` Ido Schimmel
2019-02-15 10:02     ` Vlad Buslov
2019-02-15 11:30       ` Ido Schimmel
2019-02-15 12:11         ` [PATCH] net: sched: matchall: verify that filter is not NULL in mall_walk() Vlad Buslov
2019-02-15 13:47           ` Ido Schimmel
2019-02-16  0:24           ` Cong Wang
2019-02-18 12:00             ` Vlad Buslov
2019-02-17 21:27           ` David Miller
2019-02-15 12:15         ` [PATCH net-next v4 07/17] net: sched: protect filter_chain list with filter_chain_lock mutex Vlad Buslov
2019-02-15 15:35         ` Vlad Buslov
2019-02-19  5:26           ` Cong Wang
2019-02-19 12:31             ` Vlad Buslov
2019-02-20 22:43               ` Cong Wang
2019-02-21 15:49                 ` Vlad Buslov
2019-02-19  5:08       ` Cong Wang
2019-02-19 15:20         ` Vlad Buslov
2019-02-20 23:00           ` Cong Wang
2019-02-21 17:11             ` Vlad Buslov
2019-02-15 22:35   ` Cong Wang
2019-02-18 11:06     ` Vlad Buslov
2019-02-18 18:31       ` Cong Wang
2019-02-11  8:55 ` [PATCH net-next v4 08/17] net: sched: introduce reference counting for tcf_proto Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 09/17] net: sched: traverse classifiers in chain with tcf_get_next_proto() Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 10/17] net: sched: refactor tp insert/delete for concurrent execution Vlad Buslov
2019-02-15 23:17   ` Cong Wang
2019-02-18 11:19     ` Vlad Buslov
2019-02-18 19:55       ` Cong Wang
2019-02-19 10:25         ` Vlad Buslov
2019-02-18 19:53   ` Cong Wang
2019-02-11  8:55 ` [PATCH net-next v4 11/17] net: sched: prevent insertion of new classifiers during chain flush Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 12/17] net: sched: track rtnl lock status when validating extensions Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 13/17] net: sched: extend proto ops with 'put' callback Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 14/17] net: sched: extend proto ops to support unlocked classifiers Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 15/17] net: sched: add flags to Qdisc class ops struct Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 16/17] net: sched: refactor tcf_block_find() into standalone functions Vlad Buslov
2019-02-11  8:55 ` [PATCH net-next v4 17/17] net: sched: unlock rules update API Vlad Buslov
2019-02-18 18:56   ` Cong Wang
2019-02-12 18:42 ` [PATCH net-next v4 00/17] Refactor classifier API to work with chain/classifiers without rtnl lock David Miller

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