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

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@nxp.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240527153955.553333-1-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 1ab17e8a72605385280fad9b7f656a6771236acc..11891505536081c2770fefac5fc73779309dd7a1 100644 (file)
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -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))

diff --git a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
index 12da0a939e3e5f2461eadb48883d4e0d024f7e34..8f12f00a4f5720725bafbedcd5e19a5a9f7ee757 100644 (file)
--- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
+++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
@@ -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",