netdev - Re: [net] ixgbe: fix parsing of TC actions for HW offload

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Message-Id: <20180531.154106.1949427114118876175.davem@davemloft.net>
Date:   Thu, 31 May 2018 15:41:06 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jeffrey.t.kirsher@...el.com
Cc:     ohlavaty@...hat.com, netdev@...r.kernel.org, nhorman@...hat.com,
        sassmann@...hat.com, jogreene@...hat.com, jhs@...atatu.com,
        jiri@...nulli.us
Subject: Re: [net] ixgbe: fix parsing of TC actions for HW offload

From: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Date: Wed, 30 May 2018 11:01:34 -0700

> From: Ondřej Hlavatý <ohlavaty@...hat.com>
> 
> The previous code was optimistic, accepting the offload of whole action
> chain when there was a single known action (drop/redirect). This results
> in offloading a rule which should not be offloaded, because its behavior
> cannot be reproduced in the hardware.
> 
> For example:
> 
> $ tc filter add dev eno1 parent ffff: protocol ip \
>     u32 ht 800: order 1 match tcp src 42 FFFF \
>     action mirred egress mirror dev enp1s16 pipe \
>     drop
> 
> The controller is unable to mirror the packet to a VF, but still
> offloads the rule by dropping the packet.
> 
> Change the approach of the function to a pessimistic one, rejecting the
> chain when an unknown action is found. This is better suited for future
> extensions.
> 
> Note that both recognized actions always return TC_ACT_SHOT, therefore
> it is safe to ignore actions behind them.
> 
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Cc: Jiri Pirko <jiri@...nulli.us>
> Signed-off-by: Ondřej Hlavatý <ohlavaty@...hat.com>
> Tested-by: Andrew Bowers <andrewx.bowers@...el.com>
> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>

This introduces a new warning with gcc-8.1.1 on Fedora 28.

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c: In function ‘ixgbe_configure_clsu32’:
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c:9311:8: warning: ‘queue’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  err = ixgbe_fdir_write_perfect_filter_82599(hw, &input->filter,
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           input->sw_idx, queue);
           ~~~~~~~~~~~~~~~~~~~~~