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Date:   Mon, 11 Feb 2019 15:15:07 +0100
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, ast@...nel.org, daniel@...earbox.net
Subject: Re: [PATCH net-next v4 01/17] net: sched: protect block state with
 mutex

Mon, Feb 11, 2019 at 09:55:32AM CET, vladbu@...lanox.com wrote:
>Currently, tcf_block doesn't use any synchronization mechanisms to protect
>critical sections that manage lifetime of its chains. block->chain_list and
>multiple variables in tcf_chain that control its lifetime assume external
>synchronization provided by global rtnl lock. Converting chain reference
>counting to atomic reference counters is not possible because cls API uses
>multiple counters and flags to control chain lifetime, so all of them must
>be synchronized in chain get/put code.
>
>Use single per-block lock to protect block data and manage lifetime of all
>chains on the block. Always take block->lock when accessing chain_list.
>Chain get and put modify chain lifetime-management data and parent block's
>chain_list, so take the lock in these functions. Verify block->lock state
>with assertions in functions that expect to be called with the lock taken
>and are called from multiple places. Take block->lock when accessing
>filter_chain_list.
>
>In order to allow parallel update of rules on single block, move all calls
>to classifiers outside of critical sections protected by new block->lock.
>Rearrange chain get and put functions code to only access protected chain
>data while holding block lock:
>- Rearrange code to only access chain reference counter and chain action
>  reference counter while holding block lock.
>- Extract code that requires block->lock from tcf_chain_destroy() into
>  standalone tcf_chain_destroy() function that is called by
>  __tcf_chain_put() in same critical section that changes chain reference
>  counters.
>
>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>

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

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