The test for bpf_iter_task_vma assumes that the output will be longer than 1 kB, as the comment above the loop says. Due to this assumption, the loop becomes infinite if the output turns to be shorter than 1 kB. The return value of read_fd_into_buffer is 0 when the end of file was reached, and len isn't being increased any more.

This commit adds a break on EOF to handle short output correctly. For the reference, this is the contents that I get when running test_progs under vmtest.sh, and it's shorter than 1 kB:

00400000-00401000 r--p 00000000 fe:00 25867 /root/bpf/test_progs 00401000-00674000 r-xp 00001000 fe:00 25867 /root/bpf/test_progs 00674000-0095f000 r--p 00274000 fe:00 25867 /root/bpf/test_progs 0095f000-00983000 r--p 0055e000 fe:00 25867 /root/bpf/test_progs 00983000-00a8a000 rw-p 00582000 fe:00 25867 /root/bpf/test_progs 00a8a000-0484e000 rw-p 00000000 00:00 0 7f6c64000000-7f6c64021000 rw-p 00000000 00:00 0 7f6c64021000-7f6c68000000 ---p 00000000 00:00 0 7f6c6ac8f000-7f6c6ac90000 r--s 00000000 00:0d 8032 anon_inode:bpf-map 7f6c6ac90000-7f6c6ac91000 ---p 00000000 00:00 0 7f6c6ac91000-7f6c6b491000 rw-p 00000000 00:00 0 7f6c6b491000-7f6c6b492000 r--s 00000000 00:0d 8032 anon_inode:bpf-map 7f6c6b492000-7f6c6b493000 rw-s 00000000 00:0d 8032 anon_inode:bpf-map 7ffc1e23d000-7ffc1e25e000 rw-p 00000000 00:00 0 7ffc1e3b8000-7ffc1e3bc000 r--p 00000000 00:00 0 7ffc1e3bc000-7ffc1e3bd000 r-xp 00000000 00:00 0 7fffffffe000-7ffffffff000 --xp 00000000 00:00 0

Fixes: e8168840e16c ("selftests/bpf: Add test for bpf_iter_task_vma") Signed-off-by: Maxim Mikityanskiy maximmi@nvidia.com --- tools/testing/selftests/bpf/prog_tests/bpf_iter.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c index 9454331aaf85..ea6823215e9c 100644 --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c @@ -1206,13 +1206,14 @@ static void test_task_vma(void) goto out;

/* Read CMP_BUFFER_SIZE (1kB) from bpf_iter. Read in small chunks - * to trigger seq_file corner cases. The expected output is much - * longer than 1kB, so the while loop will terminate. + * to trigger seq_file corner cases. */ len = 0; while (len < CMP_BUFFER_SIZE) { err = read_fd_into_buffer(iter_fd, task_vma_output + len, min(read_size, CMP_BUFFER_SIZE - len)); + if (!err) + break; if (CHECK(err < 0, "read_iter_fd", "read_iter_fd failed\n")) goto out; len += err;