netdev - Re: [RFC PATCH net-next] net: sched: flower: refactor reoffload for concurrent access

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Message-ID: <vbfef5zuqpd.fsf@mellanox.com>
Date:   Thu, 18 Apr 2019 18:13:37 +0000
From:   Vlad Buslov <vladbu@...lanox.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     Vlad Buslov <vladbu@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "jhs@...atatu.com" <jhs@...atatu.com>,
        "xiyou.wangcong@...il.com" <xiyou.wangcong@...il.com>,
        "jiri@...nulli.us" <jiri@...nulli.us>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [RFC PATCH net-next] net: sched: flower: refactor reoffload for
 concurrent access


On Thu 18 Apr 2019 at 21:02, Jakub Kicinski <jakub.kicinski@...ronome.com> wrote:
> On Thu, 18 Apr 2019 17:58:26 +0000, Vlad Buslov wrote:
>> On Thu 18 Apr 2019 at 20:46, Jakub Kicinski <jakub.kicinski@...ronome.com> wrote:
>> > On Thu, 18 Apr 2019 16:33:22 +0000, Vlad Buslov wrote:  
>> >> Considering this, I tried to improve my solution to remove possibility
>> >> of multiple adds of same filter and it seems to me that it would be
>> >> enough to move hw_filters list management in flower offloads functions:
>> >> add filter to list while holding rtnl lock in fl_hw_replace_filter() and
>> >> remove it from list while holding rtnl lock in fl_hw_destroy_filter().
>> >> What do you think?  
>> >
>> > Sounds good for now, but I presume the plan is to get rid of rtnl
>> > around the driver call.. at which point we would switch to a rwlock? :)  
>> 
>> Yes, but I would like the lock to be in cls hw offloads API
>> (tc_setup_cb_replace(), etc) and not in flower itself. That would also
>> solve deadlock issue and make code reusable for any further unlocked
>> classifiers implementations.
>
> And then the HW list goes along with it into the common code?
> That'd be quite nice.

The goal is to have a lock in tcf_block and use it synchronize cb_list
and all related counters (offloadcnt, etc). Now I also want to use it to
protect hw_filters list and prevent the double-add issue. Meanwhile rtnl
lock can do the job.