[PATCH 5.4 051/129] selftests/bpf: Fix massive output from test_maps

[Greg Kroah-Hartman]

From: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/bpf/159842985651.1050885.2154399297503372406.stgit@firesoul
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 c812f0178b643..1c4219ceced2f 100644
--- a/tools/testing/selftests/bpf/test_maps.c
+++ b/tools/testing/selftests/bpf/test_maps.c
@@ -1282,6 +1282,8 @@ 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) {
-- 
2.25.1