Commit e6341341 authored by Vladimir Oltean's avatar Vladimir Oltean Committed by Jakub Kicinski
Browse files

net/sched: taprio: make q->picos_per_byte available to fill_sched_entry() 



In commit b5b73b26 ("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: 09dbdf28 ("net/sched: taprio: fix calculation of maximum gate durations")
Signed-off-by: default avatarVladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: default avatarEric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240527153955.553333-1-vladimir.oltean@nxp.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 56a5cf53

net/sched/sch_taprio.c

+3 −1
Original line number Diff line number Diff line
@@ -1848,6 +1848,9 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt, 
	}

	q->flags = taprio_flags;



	/* Needed for length_to_duration() during netlink attribute parsing */

	taprio_set_picos_per_byte(dev, q);



	err = taprio_parse_mqprio_opt(dev, mqprio, extack, q->flags);

	if (err < 0)

		return err;
@@ -1907,7 +1910,6 @@ static int taprio_change(struct Qdisc *sch, struct nlattr *opt, 
	if (err < 0)

		goto free_sched;



	taprio_set_picos_per_byte(dev, q);

	taprio_update_queue_max_sdu(q, new_admin, stab);



	if (FULL_OFFLOAD_IS_ENABLED(q->flags))

tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json

+22 −0
Original line number Diff line number Diff line
@@ -132,6 +132,28 @@ 
            "echo \"1\" > /sys/bus/netdevsim/del_device"

        ]

    },

    {

        "id": "6f62",

        "name": "Add taprio Qdisc with too short interval",

        "category": [

            "qdisc",

            "taprio"

        ],

        "plugins": {

            "requires": "nsPlugin"

        },

        "setup": [

            "echo \"1 1 8\" > /sys/bus/netdevsim/new_device"

        ],

        "cmdUnderTest": "$TC qdisc add dev $ETH root handle 1: taprio num_tc 2 queues 1@0 1@1 sched-entry S 01 300 sched-entry S 02 1700 clockid CLOCK_TAI",

        "expExitCode": "2",

        "verifyCmd": "$TC qdisc show dev $ETH",

        "matchPattern": "qdisc taprio 1: root refcnt",

        "matchCount": "0",

        "teardown": [

            "echo \"1\" > /sys/bus/netdevsim/del_device"

        ]

    },

    {

        "id": "3e1e",

        "name": "Add taprio Qdisc with an invalid cycle-time",