test/zdtm: add a new test to check robust list after C/R

Added a test that validates that robust futex lists remain functional and
registered with the kernel following a CRIU restore. It simulates a scenario
where a thread holds a "robust" lock across a checkpoint, is restored, and
then terminates abruptly. The test passes if the kernel successfully
performs the OWNER_DIED cleanup on the restored futex, proving that the
robust list pointer and its associated memory offsets were correctly
re-registered during the restore process.

Fixes: #125

Assisted-by: Gemini CLI <https://gemini.google.com/>
Signed-off-by: Imranullah Khan <imranullahkhann2004@gmail.com>

test/zdtm/static/Makefile

@@ -19,6 +19,7 @@ TST_NOFILE	:=				\
 		arm-neon00			\
 		futex				\
 		futex-rl			\
+		futex-rl01			\
 		mmx00				\
 		sse00				\
 		sse20				\
@@ -599,6 +600,8 @@ futex:			CFLAGS += -pthread
 futex:			LDFLAGS += -pthread
 futex-rl:		CFLAGS += -pthread
 futex-rl:		LDFLAGS += -pthread
+futex-rl01:		CFLAGS += -pthread
+futex-rl01:		LDFLAGS += -pthread
 jobctl00:		LDLIBS += -lutil
 socket_listen:		LDLIBS += -lrt -pthread
 socket_aio:		LDLIBS += -lrt -pthread

test/zdtm/static/futex-rl01.c

@@ -0,0 +1,97 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/mman.h>
+#include <sys/syscall.h>
+#include <linux/futex.h>
+#include <stddef.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Verify robust futex list cleanup survives C/R";
+const char *test_author = "Imranullah Khan <imranullahkhann2004@gmail.com>";
+
+struct shared_state {
+	struct robust_list_head head;
+	struct robust_list entry;
+	int futex;
+	task_waiter_t waiter;
+};
+
+static pid_t __gettid(void)
+{
+	return syscall(__NR_gettid);
+}
+
+void *worker_fn(void *arg)
+{
+	struct shared_state *s = arg;
+
+	s->entry.next = &s->entry;
+	s->head.list.next = &s->entry;
+	s->head.futex_offset =
+		offsetof(struct shared_state, futex) -
+		offsetof(struct shared_state, entry);
+	s->head.list_op_pending = NULL;
+
+	if (syscall(__NR_set_robust_list, &s->head, sizeof(s->head))) {
+		fail("set_robust_list failed");
+		return NULL;
+	}
+
+	s->futex = __gettid();
+
+	test_msg("Worker %d acquired futex\n", s->futex);
+
+	task_waiter_complete(&s->waiter, 1);
+
+	task_waiter_wait4(&s->waiter, 2);
+
+	test_msg("Worker exiting while holding futex\n");
+
+	return NULL;
+}
+
+int main(int argc, char **argv)
+{
+	pthread_t thread;
+	struct shared_state *s;
+
+	test_init(argc, argv);
+
+	s = mmap(NULL, sizeof(*s),
+		 PROT_READ | PROT_WRITE,
+		 MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+	if (s == MAP_FAILED) {
+		fail("mmap failed");
+		return 1;
+	}
+
+	s->futex = 0;
+	task_waiter_init(&s->waiter);
+
+	if (pthread_create(&thread, NULL, worker_fn, s)) {
+		fail("pthread_create failed");
+		return 1;
+	}
+
+	task_waiter_wait4(&s->waiter, 1);
+
+	test_daemon();
+	test_waitsig();
+
+	task_waiter_complete(&s->waiter, 2);
+	pthread_join(thread, NULL);
+
+	test_msg("Post-exit futex value: 0x%x\n", s->futex);
+
+	if (s->futex & FUTEX_OWNER_DIED)
+		pass();
+	else
+		fail("OWNER_DIED not set - robust futex cleanup failed");
+
+	munmap(s, sizeof(*s));
+	return 0;
+}