Re: [PATCH net v5 2/2] selftests/tc-testing: add taprio test for class dump after child delete

Jamal Hadi Salim
2026-04-26T11:00:12Z

On Wed, Apr 22, 2026 at 12:20 PM Weiming Shi <bestswngs@gmail.com> wrote:
>
> Add a regression test for the NULL pointer dereference fixed in the
> previous commit. Before the fix, taprio_graft() stored NULL into
> q->qdiscs[cl - 1] when an explicitly grafted child qdisc was deleted
> via RTM_DELQDISC; the next RTM_GETTCLASS dump then crashed the kernel
> in taprio_dump_class() while reading child->handle.
>
> The test installs a taprio root qdisc on a multi-queue netdevsim
> device, grafts a pfifo child onto class 8001:1, deletes that child,
> and then performs a class dump. On a fixed kernel the dump succeeds
> and all eight taprio classes are listed; on an unpatched kernel the
> class dump crashes, which surfaces as a test failure.
>
> Signed-off-by: Weiming Shi <bestswngs@gmail.com>
> Assisted-by: Claude:claude-opus-4-6

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

cheers,
jamal
> ---
> .../tc-testing/tc-tests/qdiscs/taprio.json | 26 +++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> 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 557fb074acf0c..cd19d05925e40 100644
> --- a/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
> +++ b/tools/testing/selftests/tc-testing/tc-tests/qdiscs/taprio.json
> @@ -302,5 +302,31 @@
> "$TC qdisc del dev $ETH root",
> "echo \"1\" > /sys/bus/netdevsim/del_device"
> ]
> + },
> + {
> + "id": "c7e1",
> + "name": "Class dump after graft and delete of explicit child qdisc",
> + "category": [
> + "qdisc",
> + "taprio"
> + ],
> + "plugins": {
> + "requires": "nsPlugin"
> + },
> + "setup": [
> + "echo \"1 1 8\" > /sys/bus/netdevsim/new_device",
> + "$TC qdisc replace dev $ETH handle 8001: parent root taprio num_tc 8 map 0 1 2 3 4 5 6 7 queues 1@0 1@1 1@2 1@3 1@4 1@5 1@6 1@7 base-time 0 sched-entry S ff 20000000 clockid CLOCK_TAI",
> + "$TC qdisc add dev $ETH parent 8001:1 handle 8002: pfifo",
> + "$TC qdisc del dev $ETH parent 8001:1 handle 8002:"
> + ],
> + "cmdUnderTest": "$TC class show dev $ETH",
> + "expExitCode": "0",
> + "verifyCmd": "$TC class show dev $ETH",
> + "matchPattern": "class taprio 8001:[0-9]+ root",
> + "matchCount": "8",
> + "teardown": [
> + "$TC qdisc del dev $ETH root",
> + "echo \"1\" > /sys/bus/netdevsim/del_device"
> + ]
> }
> ]
> --
> 2.43.0
>