Re: [PATCH bpf-next v6 5/5] selftests/bpf: Add test for open coded dmabuf_iter

["T.J. Mercier" <tjmercier@google.com>]

On Wed, May 14, 2025 at 2:00 PM Song Liu <song@kernel.org> wrote:
>
> On Tue, May 13, 2025 at 9:36 AM T.J. Mercier <tjmercier@google.com> wrote:
> >
> > Use the same test buffers as the traditional iterator and a new BPF map
> > to verify the test buffers can be found with the open coded dmabuf
> > iterator.
> >
> > Signed-off-by: T.J. Mercier <tjmercier@google.com>
> > Acked-by: Christian König <christian.koenig@amd.com>
> > Acked-by: Song Liu <song@kernel.org>
> > ---
> >  .../testing/selftests/bpf/bpf_experimental.h  |  5 +++
> >  .../selftests/bpf/prog_tests/dmabuf_iter.c    | 41 +++++++++++++++++++
> >  .../testing/selftests/bpf/progs/dmabuf_iter.c | 38 +++++++++++++++++
> >  3 files changed, 84 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/bpf_experimental.h b/tools/testing/selftests/bpf/bpf_experimental.h
> > index 6535c8ae3c46..5e512a1d09d1 100644
> > --- a/tools/testing/selftests/bpf/bpf_experimental.h
> > +++ b/tools/testing/selftests/bpf/bpf_experimental.h
> > @@ -591,4 +591,9 @@ extern int bpf_iter_kmem_cache_new(struct bpf_iter_kmem_cache *it) __weak __ksym
> >  extern struct kmem_cache *bpf_iter_kmem_cache_next(struct bpf_iter_kmem_cache *it) __weak __ksym;
> >  extern void bpf_iter_kmem_cache_destroy(struct bpf_iter_kmem_cache *it) __weak __ksym;
> >
> > +struct bpf_iter_dmabuf;
> > +extern int bpf_iter_dmabuf_new(struct bpf_iter_dmabuf *it) __weak __ksym;
> > +extern struct dma_buf *bpf_iter_dmabuf_next(struct bpf_iter_dmabuf *it) __weak __ksym;
> > +extern void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) __weak __ksym;
> > +
> >  #endif
> > diff --git a/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c b/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
> > index dc740bd0e2bd..6c2b0c3dbcd8 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
> > @@ -219,14 +219,52 @@ static void subtest_dmabuf_iter_check_default_iter(struct dmabuf_iter *skel)
> >         close(iter_fd);
> >  }
> >
> > +static void subtest_dmabuf_iter_check_open_coded(struct dmabuf_iter *skel, int map_fd)
> > +{
> > +       LIBBPF_OPTS(bpf_test_run_opts, topts);
> > +       char key[DMA_BUF_NAME_LEN];
> > +       int err, fd;
> > +       bool found;
> > +
> > +       /* No need to attach it, just run it directly */
> > +       fd = bpf_program__fd(skel->progs.iter_dmabuf_for_each);
> > +
> > +       err = bpf_prog_test_run_opts(fd, &topts);
> > +       if (!ASSERT_OK(err, "test_run_opts err"))
> > +               return;
> > +       if (!ASSERT_OK(topts.retval, "test_run_opts retval"))
> > +               return;
> > +
> > +       if (!ASSERT_OK(bpf_map_get_next_key(map_fd, NULL, key), "get next key"))
> > +               return;
> > +
> > +       do {
> > +               ASSERT_OK(bpf_map_lookup_elem(map_fd, key, &found), "lookup");
> > +               ASSERT_TRUE(found, "found test buffer");
>
> This check failed once in the CI, on s390:
>
> Error: #89/3 dmabuf_iter/open_coded
> 9309 subtest_dmabuf_iter_check_open_coded:PASS:test_run_opts err 0 nsec
> 9310 subtest_dmabuf_iter_check_open_coded:PASS:test_run_opts retval 0 nsec
> 9311 subtest_dmabuf_iter_check_open_coded:PASS:get next key 0 nsec
> 9312 subtest_dmabuf_iter_check_open_coded:PASS:lookup 0 nsec
> 9313 subtest_dmabuf_iter_check_open_coded:FAIL:found test buffer
> unexpected found test buffer: got FALSE
>
> But it passed in the rerun. It is probably a bit flakey. Maybe we need some
> barrier somewhere.
>
> Here is the failure:
>
> https://github.com/kernel-patches/bpf/actions/runs/15002058808/job/42234864754
>
> To see the log, you need to log in GitHub.
>
> Thanks,
> Song

Thanks, yeah I have been trying to run this locally today but still
working on setting up an environment for it. Daniel Xu thoughtfully
suggested I use a github PR to trigger CI, but I tried that last week
without success: https://github.com/kernel-patches/bpf/pull/8910

I'm not sure if this is the cause (doesn't show up on the runs that
pass) but I have no idea why that would be intermittently failing:
libbpf: Error in bpf_create_map_xattr(testbuf_hash): -EINVAL. Retrying
without BTF.





> > +       } while (bpf_map_get_next_key(map_fd, key, key));
> > +}
>
> [...]