selftests/namespace: first threaded active reference count test

Test that namespace becomes inactive after thread exits. This verifies
active reference counting works with threads, not just processes.

Link: https://patch.msgid.link/20251029-work-namespace-nstree-listns-v4-67-2e6f823ebdc0@kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

tools/testing/selftests/namespaces/ns_active_ref_test.c

@@ -12,9 +12,12 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/syscall.h>
 #include <unistd.h>
+#include <pthread.h>
 #include "../kselftest_harness.h"
 #include "../filesystems/utils.h"
+#include "wrappers.h"
 
 #ifndef FD_NSFS_ROOT
 #define FD_NSFS_ROOT -10003 /* Root of the nsfs filesystem */
@@ -2113,4 +2116,139 @@ TEST(ns_mixed_types_same_owner)
 	ASSERT_LT(u_fd, 0);
 }
 
+/* Thread test helpers and structures */
+struct thread_ns_info {
+	__u64 ns_id;
+	int pipefd;
+	int syncfd_read;
+	int syncfd_write;
+	int exit_code;
+};
+
+static void *thread_create_namespace(void *arg)
+{
+	struct thread_ns_info *info = (struct thread_ns_info *)arg;
+	int ret;
+
+	/* Create new network namespace */
+	ret = unshare(CLONE_NEWNET);
+	if (ret < 0) {
+		info->exit_code = 1;
+		return NULL;
+	}
+
+	/* Get namespace ID */
+	int fd = open("/proc/thread-self/ns/net", O_RDONLY);
+	if (fd < 0) {
+		info->exit_code = 2;
+		return NULL;
+	}
+
+	ret = ioctl(fd, NS_GET_ID, &info->ns_id);
+	close(fd);
+	if (ret < 0) {
+		info->exit_code = 3;
+		return NULL;
+	}
+
+	/* Send namespace ID to main thread */
+	if (write(info->pipefd, &info->ns_id, sizeof(info->ns_id)) != sizeof(info->ns_id)) {
+		info->exit_code = 4;
+		return NULL;
+	}
+
+	/* Wait for signal to exit */
+	char sync_byte;
+	if (read(info->syncfd_read, &sync_byte, 1) != 1) {
+		info->exit_code = 5;
+		return NULL;
+	}
+
+	info->exit_code = 0;
+	return NULL;
+}
+
+/*
+ * Test that namespace becomes inactive after thread exits.
+ * This verifies active reference counting works with threads, not just processes.
+ */
+TEST(thread_ns_inactive_after_exit)
+{
+	pthread_t thread;
+	struct thread_ns_info info;
+	struct file_handle *handle;
+	int pipefd[2];
+	int syncpipe[2];
+	int ret;
+	char sync_byte;
+	char buf[sizeof(*handle) + MAX_HANDLE_SZ];
+
+	ASSERT_EQ(pipe(pipefd), 0);
+	ASSERT_EQ(pipe(syncpipe), 0);
+
+	info.pipefd = pipefd[1];
+	info.syncfd_read = syncpipe[0];
+	info.syncfd_write = -1;
+	info.exit_code = -1;
+
+	/* Create thread that will create a namespace */
+	ret = pthread_create(&thread, NULL, thread_create_namespace, &info);
+	ASSERT_EQ(ret, 0);
+
+	/* Read namespace ID from thread */
+	__u64 ns_id;
+	ret = read(pipefd[0], &ns_id, sizeof(ns_id));
+	if (ret != sizeof(ns_id)) {
+		sync_byte = 'X';
+		write(syncpipe[1], &sync_byte, 1);
+		pthread_join(thread, NULL);
+		close(pipefd[0]);
+		close(pipefd[1]);
+		close(syncpipe[0]);
+		close(syncpipe[1]);
+		SKIP(return, "Failed to read namespace ID from thread");
+	}
+
+	TH_LOG("Thread created namespace with ID %llu", (unsigned long long)ns_id);
+
+	/* Construct file handle */
+	handle = (struct file_handle *)buf;
+	handle->handle_bytes = sizeof(struct nsfs_file_handle);
+	handle->handle_type = FILEID_NSFS;
+	struct nsfs_file_handle *fh = (struct nsfs_file_handle *)handle->f_handle;
+	fh->ns_id = ns_id;
+	fh->ns_type = 0;
+	fh->ns_inum = 0;
+
+	/* Namespace should be active while thread is alive */
+	TH_LOG("Attempting to open namespace while thread is alive (should succeed)");
+	int nsfd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+	ASSERT_GE(nsfd, 0);
+	close(nsfd);
+
+	/* Signal thread to exit */
+	TH_LOG("Signaling thread to exit");
+	sync_byte = 'X';
+	ASSERT_EQ(write(syncpipe[1], &sync_byte, 1), 1);
+	close(syncpipe[1]);
+
+	/* Wait for thread to exit */
+	ASSERT_EQ(pthread_join(thread, NULL), 0);
+	close(pipefd[0]);
+	close(pipefd[1]);
+	close(syncpipe[0]);
+
+	if (info.exit_code != 0)
+		SKIP(return, "Thread failed to create namespace");
+
+	TH_LOG("Thread exited, namespace should be inactive");
+
+	/* Namespace should now be inactive */
+	nsfd = open_by_handle_at(FD_NSFS_ROOT, handle, O_RDONLY);
+	ASSERT_LT(nsfd, 0);
+	/* Should fail with ENOENT (inactive) or ESTALE (gone) */
+	TH_LOG("Namespace inactive as expected: %s (errno=%d)", strerror(errno), errno);
+	ASSERT_TRUE(errno == ENOENT || errno == ESTALE);
+}
+
 TEST_HARNESS_MAIN