Subject: Re: [PATCH bpf 2/2] selftests/bpf: Extend tcx tests to cover late tcx_entry release

From: Martin KaFai Lau <[email-masked]>
Date: Mon, 8 Jul 2024 15:34:13 -0700

On 7/8/24 6:31 AM, Daniel Borkmann wrote:
> Add a test case which replaces an active ingress qdisc while keeping the
> miniq in-tact during the transition period to the new clsact qdisc.

Thanks for the explanation in patch 1 fix and the test. Applied.

> 
>    # ./vmtest.sh -- ./test_progs -t tc_link
>    [...]
>    ./test_progs -t tc_link
>    [    3.412871] bpf_testmod: loading out-of-tree module taints kernel.
>    [    3.413343] bpf_testmod: module verification failed: signature and/or required key missing - tainting kernel
>    #332     tc_links_after:OK
>    #333     tc_links_append:OK
>    #334     tc_links_basic:OK
>    #335     tc_links_before:OK
>    #336     tc_links_chain_classic:OK
>    #337     tc_links_chain_mixed:OK
>    #338     tc_links_dev_chain0:OK
>    #339     tc_links_dev_cleanup:OK
>    #340     tc_links_dev_mixed:OK
>    #341     tc_links_ingress:OK
>    #342     tc_links_invalid:OK
>    #343     tc_links_prepend:OK
>    #344     tc_links_replace:OK
>    #345     tc_links_revision:OK
>    Summary: 14/0 PASSED, 0 SKIPPED, 0 FAILED
> 
> Signed-off-by: Daniel Borkmann <[email-masked]>
> Cc: Martin KaFai Lau <[email-masked]>
> ---
>   tools/testing/selftests/bpf/config            |  3 +
>   .../selftests/bpf/prog_tests/tc_links.c       | 61 +++++++++++++++++++
>   2 files changed, 64 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
> index c0ef168eb637..c95f6f1ab74a 100644
> --- a/tools/testing/selftests/bpf/config
> +++ b/tools/testing/selftests/bpf/config
> @@ -61,9 +61,12 @@ CONFIG_MPLS=y
>   CONFIG_MPLS_IPTUNNEL=y
>   CONFIG_MPLS_ROUTING=y
>   CONFIG_MPTCP=y
> +CONFIG_NET_ACT_SKBMOD=y
> +CONFIG_NET_CLS=y
>   CONFIG_NET_CLS_ACT=y
>   CONFIG_NET_CLS_BPF=y
>   CONFIG_NET_CLS_FLOWER=y
> +CONFIG_NET_CLS_MATCHALL=y
>   CONFIG_NET_FOU=y
>   CONFIG_NET_FOU_IP_TUNNELS=y
>   CONFIG_NET_IPGRE=y
> diff --git a/tools/testing/selftests/bpf/prog_tests/tc_links.c b/tools/testing/selftests/bpf/prog_tests/tc_links.c
> index bc9841144685..1af9ec1149aa 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tc_links.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tc_links.c
> @@ -9,6 +9,8 @@
>   #define ping_cmd "ping -q -c1 -w1 127.0.0.1 > /dev/null"
>   
>   #include "test_tc_link.skel.h"
> +
> +#include "netlink_helpers.h"
>   #include "tc_helpers.h"
>   
>   void serial_test_tc_links_basic(void)
> @@ -1787,6 +1789,65 @@ void serial_test_tc_links_ingress(void)
>   	test_tc_links_ingress(BPF_TCX_INGRESS, false, false);
>   }
>   
> +struct qdisc_req {
> +	struct nlmsghdr  n;
> +	struct tcmsg     t;
> +	char             buf[1024];
> +};
> +
> +static int qdisc_replace(int ifindex, const char *kind, bool block)
> +{
> +	struct rtnl_handle rth = { .fd = -1 };
> +	struct qdisc_req req;
> +	int err;
> +
> +	err = rtnl_open(&rth, 0);
> +	if (!ASSERT_OK(err, "open_rtnetlink"))
> +		return err;
> +
> +	memset(&req, 0, sizeof(req));
> +	req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct tcmsg));
> +	req.n.nlmsg_flags = NLM_F_CREATE | NLM_F_REPLACE | NLM_F_REQUEST;
> +	req.n.nlmsg_type = RTM_NEWQDISC;
> +	req.t.tcm_family = AF_UNSPEC;
> +	req.t.tcm_ifindex = ifindex;
> +	req.t.tcm_parent = 0xfffffff1;
> +
> +	addattr_l(&req.n, sizeof(req), TCA_KIND, kind, strlen(kind) + 1);
> +	if (block)
> +		addattr32(&req.n, sizeof(req), TCA_INGRESS_BLOCK, 1);
> +
> +	err = rtnl_talk(&rth, &req.n, NULL);
> +	ASSERT_OK(err, "talk_rtnetlink");
> +	rtnl_close(&rth);
> +	return err;
> +}
> +
> +void serial_test_tc_links_dev_chain0(void)
> +{
> +	int err, ifindex;
> +
> +	ASSERT_OK(system("ip link add dev foo type veth peer name bar"), "add veth");
> +	ifindex = if_nametoindex("foo");
> +	ASSERT_NEQ(ifindex, 0, "non_zero_ifindex");
> +	err = qdisc_replace(ifindex, "ingress", true);
> +	if (!ASSERT_OK(err, "attaching ingress"))
> +		goto cleanup;
> +	ASSERT_OK(system("tc filter add block 1 matchall action skbmod swap mac"), "add block");
> +	err = qdisc_replace(ifindex, "clsact", false);
> +	if (!ASSERT_OK(err, "attaching clsact"))
> +		goto cleanup;
> +	/* Heuristic: kern_sync_rcu() alone does not work; a wait-time of ~5s
> +	 * triggered the issue without the fix reliably 100% of the time.
> +	 */
> +	sleep(5);

It may be handy to be able to trigger rcu_barrier() to wait for the pending rcu 
callbacks to finish. Not sure if there is an existing way to do that without 
introducing a kfunc in bpf_testmod. Probably something to think about as an 
optimization.

Thanks for the fix and the test. Applied.

> +	ASSERT_OK(system("tc filter add dev foo ingress matchall action skbmod swap mac"), "add filter");
> +cleanup:
> +	ASSERT_OK(system("ip link del dev foo"), "del veth");
> +	ASSERT_EQ(if_nametoindex("foo"), 0, "foo removed");
> +	ASSERT_EQ(if_nametoindex("bar"), 0, "bar removed");
> +}
> +
>   static void test_tc_links_dev_mixed(int target)
>   {
>   	LIBBPF_OPTS(bpf_tc_opts, tc_opts, .handle = 1, .priority = 1);