From: Geliang Tang <tanggeliang@kylinos.cn>

Fix the pidfd leak in kselftest_harness.h's __wait_for_test() where
childfd = syscall(__NR_pidfd_open, t->pid, 0) is never closed.

Fixes: 73a3cde97677 ("selftests: harness: Implement test timeouts through pidfd")
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
v2:
 - move close() directly after poll() as Thomas suggested.

Hi,

While adding more TLS selftests for MPTCP KTLS development, a segmentation
fault occurred. Debugging revealed that the accept() failure was due to MPTCP
tests requiring over 1024 file descriptors simultaneously. I initially raised
the limit to 4096 in [1], but sashiko noted that the real issue was a pidfd
leak in kselftest_harness.h's __wait_for_test(). Hence, this fix addresses that.

Thanks,
-Geliang

[1]
https://patchwork.kernel.org/project/mptcp/patch/ced184831757eaae9e690f65d799809ed22cae28.1776469069.git.tanggeliang@kylinos.cn/
---
 tools/testing/selftests/kselftest_harness.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 75fb016cd190..53535c188b33 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -996,6 +996,7 @@ static void __wait_for_test(struct __test_metadata *t)
 	poll_child.fd = childfd;
 	poll_child.events = POLLIN;
 	ret = poll(&poll_child, 1, t->timeout * 1000);
+	close(childfd);
 	if (ret == -1) {
 		t->exit_code = KSFT_FAIL;
 		fprintf(TH_LOG_STREAM,
-- 
2.51.0

Hi Geliang,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal (except selftest_mptcp_join): Success! ✅
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Unstable: 1 failed test(s): packetdrill_dss ⚠️ 
- KVM Validation: debug (only selftest_mptcp_join): Success! ✅
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/24659860268

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/dbc5b80ffca6
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1083220


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)

On Mon, Apr 20, 2026 at 05:45:28PM +0800, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> Fix the pidfd leak in kselftest_harness.h's __wait_for_test() where
> childfd = syscall(__NR_pidfd_open, t->pid, 0) is never closed.
> 
> Fixes: 73a3cde97677 ("selftests: harness: Implement test timeouts through pidfd")
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>

Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

(...)