From: Jesper Dangaard Brouer <brouer@redhat.com> [ Upstream commit fa4505675e093e895b7ec49a76d44f6b5ad9602e ] When stdout output from the selftests tool 'test_maps' gets redirected into e.g file or pipe, then the output lines increase a lot (from 21 to 33949 lines). This is caused by the printf that happens before the fork() call, and there are user-space buffered printf data that seems to be duplicated into the forked process. To fix this fflush() stdout before the fork loop in __run_parallel(). Fixes: 1a97cf1fe503 ("selftests/bpf: speedup test_maps") Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/159842985651.1050885.2154399297503372406.stgit@f... Signed-off-by: Sasha Levin <sashal@kernel.org> --- tools/testing/selftests/bpf/test_maps.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c index 9b552c0fc47d..4e202217fae1 100644 --- a/tools/testing/selftests/bpf/test_maps.c +++ b/tools/testing/selftests/bpf/test_maps.c @@ -1017,6 +1017,8 @@ static void __run_parallel(int tasks, void (*fn)(int task, void *data), pid_t pid[tasks]; int i; + fflush(stdout); + for (i = 0; i < tasks; i++) { pid[i] = fork(); if (pid[i] == 0) { -- 2.25.1