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

[David Miller <davem@davemloft.net>]

From: Vlad Buslov <vladbu@mellanox.com>
Date: Fri,  5 Apr 2019 20:56:26 +0300

> 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@netronome.com>
> Signed-off-by: Vlad Buslov <vladbu@mellanox.com>

Applied, thanks Vlad.