netdev - Re: [PATCH net-next] net: sched: flower: insert filter to ht before offloading it to hw

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Date:   Sat, 6 Apr 2019 07:59:45 +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, john.hurley@...ronome.com
Subject: Re: [PATCH net-next] net: sched: flower: insert filter to ht before
 offloading it to hw

Fri, Apr 05, 2019 at 07:56:26PM CEST, vladbu@...lanox.com wrote:
>John reports:
>
>Recent refactoring of fl_change aims to use the classifier spinlock to
>avoid the need for rtnl lock. In doing so, the fl_hw_replace_filer()
>function was moved to before the lock is taken. This can create problems
>for drivers if duplicate filters are created (commmon in ovs tc offload
>due to filters being triggered by user-space matches).
>
>Drivers registered for such filters will now receive multiple copies of
>the same rule, each with a different cookie value. This means that the
>drivers would need to do a full match field lookup to determine
>duplicates, repeating work that will happen in flower __fl_lookup().
>Currently, drivers do not expect to receive duplicate filters.
>
>To fix this, verify that filter with same key is not present in flower
>classifier hash table and insert the new filter to the flower hash table
>before offloading it to hardware. Implement helper function
>fl_ht_insert_unique() to atomically verify/insert a filter.
>
>This change makes filter visible to fast path at the beginning of
>fl_change() function, which means it can no longer be freed directly in
>case of error. Refactor fl_change() error handling code to deallocate the
>filter with rcu timeout.
>
>Fixes: 620da4860827 ("net: sched: flower: refactor fl_change")
>Reported-by: John Hurley <john.hurley@...ronome.com>
>Signed-off-by: Vlad Buslov <vladbu@...lanox.com>

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