[Linaro-mm-sig] 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@google.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@google.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