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Message-Id: <20251022-work-namespace-nstree-listns-v2-22-71a588572371@kernel.org>
Date: Wed, 22 Oct 2025 18:06:00 +0200
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
Jeff Layton <jlayton@...nel.org>
Cc: Jann Horn <jannh@...gle.com>, Mike Yuan <me@...dnzj.com>,
Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>,
Lennart Poettering <mzxreary@...inter.de>,
Daan De Meyer <daan.j.demeyer@...il.com>, Aleksa Sarai <cyphar@...har.com>,
Amir Goldstein <amir73il@...il.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>, Thomas Gleixner <tglx@...utronix.de>,
Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, bpf@...r.kernel.org,
Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
netdev@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Christian Brauner <brauner@...nel.org>
Subject: [PATCH v2 22/63] selftests/namespaces: third active reference
count tests
Test that a namespace remains active while a process is using it,
even after the creating process exits.
Signed-off-by: Christian Brauner <brauner@...nel.org>
---
.../selftests/namespaces/ns_active_ref_test.c | 128 +++++++++++++++++++++
1 file changed, 128 insertions(+)
diff --git a/tools/testing/selftests/namespaces/ns_active_ref_test.c b/tools/testing/selftests/namespaces/ns_active_ref_test.c
index f628b4a4a927..63233f22517a 100644
--- a/tools/testing/selftests/namespaces/ns_active_ref_test.c
+++ b/tools/testing/selftests/namespaces/ns_active_ref_test.c
@@ -160,4 +160,132 @@ TEST(ns_inactive_after_exit)
}
}
+/*
+ * Test that a namespace remains active while a process is using it,
+ * even after the creating process exits.
+ */
+TEST(ns_active_with_multiple_processes)
+{
+ struct file_handle *handle;
+ int mount_id;
+ int ret;
+ int fd;
+ int pipefd[2];
+ int syncpipe[2];
+ pid_t pid1, pid2;
+ int status;
+ char buf[sizeof(*handle) + MAX_HANDLE_SZ];
+ char sync_byte;
+
+ /* Create pipes for communication */
+ ASSERT_EQ(pipe(pipefd), 0);
+ ASSERT_EQ(pipe(syncpipe), 0);
+
+ pid1 = fork();
+ ASSERT_GE(pid1, 0);
+
+ if (pid1 == 0) {
+ /* First child - creates namespace */
+ close(pipefd[0]);
+ close(syncpipe[1]);
+
+ /* Create new network namespace */
+ ret = unshare(CLONE_NEWNET);
+ if (ret < 0) {
+ close(pipefd[1]);
+ close(syncpipe[0]);
+ exit(1);
+ }
+
+ /* Open and get handle */
+ fd = open("/proc/self/ns/net", O_RDONLY);
+ if (fd < 0) {
+ close(pipefd[1]);
+ close(syncpipe[0]);
+ exit(1);
+ }
+
+ handle = (struct file_handle *)buf;
+ handle->handle_bytes = MAX_HANDLE_SZ;
+ ret = name_to_handle_at(fd, "", handle, &mount_id, AT_EMPTY_PATH);
+ close(fd);
+
+ if (ret < 0) {
+ close(pipefd[1]);
+ close(syncpipe[0]);
+ exit(1);
+ }
+
+ /* Send handle to parent */
+ write(pipefd[1], buf, sizeof(*handle) + handle->handle_bytes);
+ close(pipefd[1]);
+
+ /* Wait for signal before exiting */
+ read(syncpipe[0], &sync_byte, 1);
+ close(syncpipe[0]);
+ exit(0);
+ }
+
+ /* Parent reads handle */
+ close(pipefd[1]);
+ ret = read(pipefd[0], buf, sizeof(buf));
+ close(pipefd[0]);
+ ASSERT_GT(ret, 0);
+
+ handle = (struct file_handle *)buf;
+
+ /* Create second child that will keep namespace active */
+ pid2 = fork();
+ ASSERT_GE(pid2, 0);
+
+ if (pid2 == 0) {
+ /* Second child - reopens the namespace */
+ close(syncpipe[0]);
+ close(syncpipe[1]);
+
+ /* Open the namespace via handle */
+ fd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+ if (fd < 0) {
+ exit(1);
+ }
+
+ /* Join the namespace */
+ ret = setns(fd, CLONE_NEWNET);
+ close(fd);
+ if (ret < 0) {
+ exit(1);
+ }
+
+ /* Sleep to keep namespace active */
+ sleep(1);
+ exit(0);
+ }
+
+ /* Let second child enter the namespace */
+ usleep(100000); /* 100ms */
+
+ /* Signal first child to exit */
+ close(syncpipe[0]);
+ sync_byte = 'X';
+ write(syncpipe[1], &sync_byte, 1);
+ close(syncpipe[1]);
+
+ /* Wait for first child */
+ waitpid(pid1, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+
+ /* Namespace should still be active because second child is using it */
+ fd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+ if (fd < 0) {
+ /* If this fails, second child might not have entered namespace yet */
+ TH_LOG("Warning: Could not reopen namespace (errno=%d)", errno);
+ } else {
+ close(fd);
+ }
+
+ /* Wait for second child */
+ waitpid(pid2, &status, 0);
+ ASSERT_TRUE(WIFEXITED(status));
+}
+
TEST_HARNESS_MAIN
--
2.47.3
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