From:   Kurt Kanzenbach <kurt@linutronix.de>
To:     Vladimir Oltean <vladimir.oltean@nxp.com>, netdev@vger.kernel.org
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Jamal Hadi Salim <jhs@mojatatu.com>,
        Cong Wang <xiyou.wangcong@gmail.com>,
        Jiri Pirko <jiri@resnulli.us>,
        Vinicius Costa Gomes <vinicius.gomes@intel.com>,
        Gerhard Engleder <gerhard@engleder-embedded.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/3] net/sched: taprio: don't allow dynamic
 max_sdu to go negative after stab adjustment
In-Reply-To: <20230215224632.2532685-3-vladimir.oltean@nxp.com>
References: <20230215224632.2532685-1-vladimir.oltean@nxp.com>
 <20230215224632.2532685-3-vladimir.oltean@nxp.com>
Date:   Thu, 16 Feb 2023 10:27:57 +0100
Message-ID: <87fsb6ot7m.fsf@kurt>
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On Thu Feb 16 2023, Vladimir Oltean wrote:
> The overhead specified in the size table comes from the user. With small
> time intervals (or gates always closed), the overhead can be larger than
> the max interval for that traffic class, and their difference is
> negative.
>
> What we want to happen is for max_sdu_dynamic to have the smallest
> non-zero value possible (1) which means that all packets on that traffic
> class are dropped on enqueue. However, since max_sdu_dynamic is u32, a
> negative is represented as a large value and oversized dropping never
> happens.
>
> Use max_t with int to force a truncation of max_frm_len to no smaller
> than dev->hard_header_len + 1, which in turn makes max_sdu_dynamic no
> smaller than 1.
>
> Fixes: fed87cc6718a ("net/sched: taprio: automatically calculate queueMaxSDU based on TC gate durations")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Kurt Kanzenbach <kurt@linutronix.de>

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