selftests/bpf: Fix massive output from test_maps

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@firesoul

diff --git a/tools/testing/selftests/bpf/test_maps.c b/tools/testing/selftests/bpf/test_maps.c
index 754cf61..0d92ebc 100644 (file)
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -1274,6 +1274,8 @@ static void __run_parallel(unsigned int tasks,
        pid_t pid[tasks];
        int i;
 
+       fflush(stdout);
+
        for (i = 0; i < tasks; i++) {
                pid[i] = fork();
                if (pid[i] == 0) {