netdev - Re: [PATCH net 1/2] net/sched: taprio: make q->picos_per_byte available to fill_sched

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Date: Tue, 28 May 2024 07:41:21 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	Vinicius Costa Gomes <vinicius.gomes@...el.com>, Jamal Hadi Salim <jhs@...atatu.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Shuah Khan <shuah@...nel.org>, Pedro Tammela <pctammela@...atatu.com>
Subject: Re: [PATCH net 1/2] net/sched: taprio: make q->picos_per_byte
 available to fill_sched_entry()

On Mon, May 27, 2024 at 5:40 PM Vladimir Oltean <vladimir.oltean@....com> wrote:
>
> In commit b5b73b26b3ca ("taprio: Fix allowing too small intervals"), a
> comparison of user input against length_to_duration(q, ETH_ZLEN) was
> introduced, to avoid RCU stalls due to frequent hrtimers.
>
> The implementation of length_to_duration() depends on q->picos_per_byte
> being set for the link speed. The blamed commit in the Fixes: tag has
> moved this too late, so the checks introduced above are ineffective.
> The q->picos_per_byte is zero at parse_taprio_schedule() ->
> parse_sched_list() -> parse_sched_entry() -> fill_sched_entry() time.
>
> Move the taprio_set_picos_per_byte() call as one of the first things in
> taprio_change(), before the bulk of the netlink attribute parsing is
> done. That's because it is needed there.
>
> Add a selftest to make sure the issue doesn't get reintroduced.
>
> Fixes: 09dbdf28f9f9 ("net/sched: taprio: fix calculation of maximum gate durations")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Thanks!