Re: [PATCH bpf-next 2/2] selftests: bpf: Add a new test for bare tracepoints

On Tue, Jan 12, 2021 at 11:27 AM Qais Yousef [off-list ref] wrote:

On 01/11/21 23:26, Andrii Nakryiko wrote:

quoted

On Mon, Jan 11, 2021 at 10:20 AM Qais Yousef [off-list ref] wrote:

quoted

Reuse module_attach infrastructure to add a new bare tracepoint to check
we can attach to it as a raw tracepoint.

Signed-off-by: Qais Yousef <redacted>
---

Andrii

I was getting the error below when I was trying to run the test.
I had to comment out all related fentry* code to be able to test the raw_tp
stuff. Not sure something I've done wrong or it's broken for some reason.
I was on v5.11-rc2.

Check that you have all the required Kconfig options from
tools/testing/selftests/bpf/config. And also you will need to build

Yep I have merged this config snippet using merge_config.sh script.

quoted

pahole from master, 1.19 doesn't have some fixes that add kernel
module support. I think pahole is the reasons why you have the failure
below.

I am using pahole 1.19. I have built it from tip of master though.

/trying using v1.19 tag

Still fails the same.

quoted

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        $ sudo ./test_progs -v -t module_attach

use -vv when debugging stuff like that with test_progs, it will output
libbpf detailed logs, that often are very helpful

I tried that but it didn't help me. Full output is here

        https://paste.debian.net/1180846

It did help a bit for me to make sure that you have bpf_testmod
properly loaded and its BTF was found, so the problem is somewhere
else. Also, given load succeeded and attach failed with OPNOTSUPP, I
suspect you are missing some of FTRACE configs, which seems to be
missing from selftests's config as well. Check that you have
CONFIG_FTRACE=y and CONFIG_DYNAMIC_FTRACE=y, and you might need some
more. See [0] for a real config we are using to run all tests in
libbpf CI. If you figure out what you were missing, please also
contribute a patch to selftests' config.

  [0] https://github.com/libbpf/libbpf/blob/master/travis-ci/vmtest/configs/latest.config

quoted

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        bpf_testmod.ko is already unloaded.
        Loading bpf_testmod.ko...
        Successfully loaded bpf_testmod.ko.
        test_module_attach:PASS:skel_open 0 nsec
        test_module_attach:PASS:set_attach_target 0 nsec
        test_module_attach:PASS:skel_load 0 nsec
        libbpf: prog 'handle_fentry': failed to attach: ERROR: strerror_r(-524)=22
        libbpf: failed to auto-attach program 'handle_fentry': -524
        test_module_attach:FAIL:skel_attach skeleton attach failed: -524
        #58 module_attach:FAIL
        Successfully unloaded bpf_testmod.ko.
        Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED

But even apart from test failure, there seems to be kernel build
failure. See [0] for what fails in kernel-patches CI.

   [0] https://travis-ci.com/github/kernel-patches/bpf/builds/212730017

Sorry about that. I did a last minute change because of checkpatch.pl error and
it seems I either forgot to rebuild or missed that the rebuild failed :/

no worries, just fix and re-submit. Good that we have CI that caught
this early on.

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 .../selftests/bpf/bpf_testmod/bpf_testmod-events.h     |  6 ++++++
 tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c  |  2 ++
 tools/testing/selftests/bpf/prog_tests/module_attach.c |  1 +
 tools/testing/selftests/bpf/progs/test_module_attach.c | 10 ++++++++++
 4 files changed, 19 insertions(+)

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
index b83ea448bc79..e1ada753f10c 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h

@@ -28,6 +28,12 @@ TRACE_EVENT(bpf_testmod_test_read,
                  __entry->pid, __entry->comm, __entry->off, __entry->len)
 );

+/* A bare tracepoint with no event associated with it */
+DECLARE_TRACE(bpf_testmod_test_read_bare,
+       TP_PROTO(struct task_struct *task, struct bpf_testmod_test_read_ctx *ctx),
+       TP_ARGS(task, ctx)
+);
+
 #endif /* _BPF_TESTMOD_EVENTS_H */

 #undef TRACE_INCLUDE_PATH

diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
index 2df19d73ca49..d63cebdaca44 100644
--- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
+++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

@@ -22,6 +22,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
        };

        trace_bpf_testmod_test_read(current, &ctx);
+       ctx.len++;
+       trace_bpf_testmod_test_read_bare(current, &ctx);

It's kind of boring to have two read tracepoints :) Do you mind adding

Hehe boring is good :p

quoted

a write tracepoint and use bare tracepoint there? You won't need this
ctx.len++ hack as well. Feel free to add identical
bpf_testmod_test_write_ctx (renaming it is more of a pain).

It was easy to get this done. So I think it should be easy to make it a write
too :)

yep, having two tracepoints allow more flexibility over longer term,
so I think it's good to do (regardless of boring or not ;) )

Thanks

--
Qais Yousef

quoted

quoted

        return -EIO; /* always fail */
 }

diff --git a/tools/testing/selftests/bpf/prog_tests/module_attach.c b/tools/testing/selftests/bpf/prog_tests/module_attach.c
index 50796b651f72..7085a118f38c 100644
--- a/tools/testing/selftests/bpf/prog_tests/module_attach.c
+++ b/tools/testing/selftests/bpf/prog_tests/module_attach.c

@@ -50,6 +50,7 @@ void test_module_attach(void)
        ASSERT_OK(trigger_module_test_read(READ_SZ), "trigger_read");

        ASSERT_EQ(bss->raw_tp_read_sz, READ_SZ, "raw_tp");
+       ASSERT_EQ(bss->raw_tp_bare_read_sz, READ_SZ+1, "raw_tp_bare");
        ASSERT_EQ(bss->tp_btf_read_sz, READ_SZ, "tp_btf");
        ASSERT_EQ(bss->fentry_read_sz, READ_SZ, "fentry");
        ASSERT_EQ(bss->fentry_manual_read_sz, READ_SZ, "fentry_manual");

diff --git a/tools/testing/selftests/bpf/progs/test_module_attach.c b/tools/testing/selftests/bpf/progs/test_module_attach.c
index efd1e287ac17..08aa157afa1d 100644
--- a/tools/testing/selftests/bpf/progs/test_module_attach.c
+++ b/tools/testing/selftests/bpf/progs/test_module_attach.c

@@ -17,6 +17,16 @@ int BPF_PROG(handle_raw_tp,
        return 0;
 }

+__u32 raw_tp_bare_read_sz = 0;
+
+SEC("raw_tp/bpf_testmod_test_read_bare")
+int BPF_PROG(handle_raw_tp_bare,
+            struct task_struct *task, struct bpf_testmod_test_read_ctx *read_ctx)
+{
+       raw_tp_bare_read_sz = BPF_CORE_READ(read_ctx, len);
+       return 0;
+}
+
 __u32 tp_btf_read_sz = 0;

 SEC("tp_btf/bpf_testmod_test_read")
--

2.25.1