linux-kernel - Re: [PATCH bpf 2/2] selftests/bpf: Add test for truncated dmabuf

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Message-ID: <CABdmKX0LxoPJPA755bzN8vRjUOQ0c4XucGhDX8QgbxqYXdB1pA@mail.gmail.com>
Date: Thu, 4 Dec 2025 08:44:59 -0800
From: "T.J. Mercier" <tjmercier@...gle.com>
To: yonghong.song@...ux.dev, ast@...nel.org, daniel@...earbox.net, 
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org, 
	john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me, 
	haoluo@...gle.com, jolsa@...nel.org, shuah@...nel.org, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	android-mm@...gle.com
Cc: christian.koenig@....com, sumit.semwal@...aro.org, 
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH bpf 2/2] selftests/bpf: Add test for truncated dmabuf_iter reads

On Wed, Dec 3, 2025 at 4:05 PM T.J. Mercier <tjmercier@...gle.com> wrote:
>
> If many dmabufs are present, reads of the dmabuf iterator can be
> truncated at PAGE_SIZE or user buffer size boundaries before the fix in
> "selftests/bpf: Add test for open coded dmabuf_iter".

Copy/paste error here. This should be "bpf: Fix truncated dmabuf
iterator reads" from the previous commit in patch 1. I didn't include
the sha because I don't think they're guaranteed to be stable at this
point.

I also saw the warning from CI about the extra newline before
subtest_dmabuf_iter_check_open_coded, but the current CI failures look
unrelated to this change.

Add a test to
> confirm truncation does not occur.
>
> Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
> ---
>  .../selftests/bpf/prog_tests/dmabuf_iter.c    | 47 +++++++++++++++++--
>  1 file changed, 42 insertions(+), 5 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c b/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
> index 6c2b0c3dbcd8..e442be9dde7e 100644
> --- a/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/dmabuf_iter.c
> @@ -73,12 +73,10 @@ static int create_udmabuf(void)
>         return -1;
>  }
>
> -static int create_sys_heap_dmabuf(void)
> +static int create_sys_heap_dmabuf(size_t bytes)
>  {
> -       sysheap_test_buffer_size = 20 * getpagesize();
> -
>         struct dma_heap_allocation_data data = {
> -               .len = sysheap_test_buffer_size,
> +               .len = bytes,
>                 .fd = 0,
>                 .fd_flags = O_RDWR | O_CLOEXEC,
>                 .heap_flags = 0,
> @@ -110,7 +108,9 @@ static int create_sys_heap_dmabuf(void)
>  static int create_test_buffers(void)
>  {
>         udmabuf = create_udmabuf();
> -       sysheap_dmabuf = create_sys_heap_dmabuf();
> +
> +       sysheap_test_buffer_size = 20 * getpagesize();
> +       sysheap_dmabuf = create_sys_heap_dmabuf(sysheap_test_buffer_size);
>
>         if (udmabuf < 0 || sysheap_dmabuf < 0)
>                 return -1;
> @@ -219,6 +219,26 @@ static void subtest_dmabuf_iter_check_default_iter(struct dmabuf_iter *skel)
>         close(iter_fd);
>  }
>
> +static void subtest_dmabuf_iter_check_lots_of_buffers(struct dmabuf_iter *skel)
> +{
> +       int iter_fd;
> +       char buf[1024];
> +       size_t total_bytes_read = 0;
> +       ssize_t bytes_read;
> +
> +       iter_fd = bpf_iter_create(bpf_link__fd(skel->links.dmabuf_collector));
> +       if (!ASSERT_OK_FD(iter_fd, "iter_create"))
> +               return;
> +
> +       while ((bytes_read = read(iter_fd, buf, sizeof(buf))) > 0)
> +               total_bytes_read += bytes_read;
> +
> +       ASSERT_GT(total_bytes_read, getpagesize(), "total_bytes_read");
> +
> +       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);
> @@ -275,6 +295,23 @@ void test_dmabuf_iter(void)
>                 subtest_dmabuf_iter_check_no_infinite_reads(skel);
>         if (test__start_subtest("default_iter"))
>                 subtest_dmabuf_iter_check_default_iter(skel);
> +       if (test__start_subtest("lots_of_buffers")) {
> +               size_t NUM_BUFS = 100;
> +               int buffers[NUM_BUFS];
> +               int i;
> +
> +               for (i = 0; i < NUM_BUFS; ++i) {
> +                       buffers[i] = create_sys_heap_dmabuf(getpagesize());
> +                       if (!ASSERT_OK_FD(buffers[i], "dmabuf_fd"))
> +                               goto cleanup_bufs;
> +               }
> +
> +               subtest_dmabuf_iter_check_lots_of_buffers(skel);
> +
> +cleanup_bufs:
> +               for (--i; i >= 0; --i)
> +                       close(buffers[i]);
> +       }
>         if (test__start_subtest("open_coded"))
>                 subtest_dmabuf_iter_check_open_coded(skel, map_fd);
>
> --
> 2.52.0.177.g9f829587af-goog
>