netdev - [PATCH bpf-next v5 11/12] bpf: selftests: Fix fd cleanup in get_branch

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Date:   Mon, 27 Sep 2021 20:29:40 +0530
From:   Kumar Kartikeya Dwivedi <memxor@...il.com>
To:     bpf@...r.kernel.org
Cc:     Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Song Liu <songliubraving@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        netdev@...r.kernel.org
Subject: [PATCH bpf-next v5 11/12] bpf: selftests: Fix fd cleanup in get_branch_snapshot

Cleanup code uses while (cpu++ < cpu_cnt) for closing fds, which means
it starts iterating from 1 for closing fds. If the first fd is -1, it
skips over it and closes garbage fds (typically zero) in the remaining
array. This leads to test failures for future tests when they end up
storing fd 0 (as the slot becomes free due to close(0)) in ldimm64's BTF
fd, ending up trying to match module BTF id with vmlinux.

This was observed as spurious CI failure for the ksym_module_libbpf and
module_attach tests. The test ends up closing fd 0 and breaking libbpf's
assumption that module BTF fd will always be > 0, which leads to the
kernel thinking that we are pointing to a BTF ID in vmlinux BTF.

Cc: Song Liu <songliubraving@...com>
Fixes: 025bd7c753aa (selftests/bpf: Add test for bpf_get_branch_snapshot)
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
---
 tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
index f81db9135ae4..67e86f8d8677 100644
--- a/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
+++ b/tools/testing/selftests/bpf/prog_tests/get_branch_snapshot.c
@@ -38,10 +38,9 @@ static int create_perf_events(void)

 static void close_perf_events(void)
 {
-	int cpu = 0;
-	int fd;
+	int cpu, fd;

-	while (cpu++ < cpu_cnt) {
+	for (cpu = 0; cpu < cpu_cnt; cpu++) {
 		fd = pfd_array[cpu];
 		if (fd < 0)
 			break;
-- 
2.33.0