zdtm: check that pid-reuse does not break iterative memory dump

The idea of the test is:

1) mmap separate page and put variable there, so that other usage does
not dirty these region. Initialize the variable with VALUE_A.

2) fork a child with special pid == CHILD_NS_PID. Only if it is a first
child overwrite the variable with VALUE_B.

3) wait for the end of the next predump or end of restore with
test_wait_pre_dump_ack/test_wait_pre_dump pair and kill our child.

Note: The memory region is "clean" in parent.

4) goto (2) unles end of cr is reported by test_waitpre

So on first iteration child with pid CHILD_NS_PID was dumped with
VALUE_B, on all other iterations and on final dump other child with the
same pid exists but with VALUE_A. But on all iterations after the first
one we have these memory region "clean". So criu before the fix would
have restored the VALUE_B taking it from first child's image, but should
restore VALUE_A.

Note: Child in its turn waits termination and performs a check that variable
value doesn't change after c/r.

We should run the test with at least one predump to trigger the problem:

[root@snorch criu]# ./test/zdtm.py run --pre 1 -k always -t zdtm/transition/pid_reuse
Checking feature ns_pid
Checking feature ns_get_userns
Checking feature ns_get_parent

=== Run 1/1 ================ zdtm/transition/pid_reuse

===================== Run zdtm/transition/pid_reuse in ns ======================
DEP       pid_reuse.d
CC        pid_reuse.o
LINK      pid_reuse
Start test
Test is SUID
./pid_reuse --pidfile=pid_reuse.pid --outfile=pid_reuse.out
Run criu pre-dump
Send the 10 signal to  52
Run criu dump
Run criu restore
Send the 15 signal to  73
Wait for zdtm/transition/pid_reuse(73) to die for 0.100000
Test output: ================================
14:47:57.717: 11235: ERR: pid_reuse.c:76: Wrong value in a variable after restore
14:47:57.717:     4: FAIL: pid_reuse.c:110: Task 11235 exited with wrong code 1 (errno = 11 (Resource temporarily unavailable))

<<< ================================

https://jira.sw.ru/browse/PSBM-67502

v3: simplify waitpid's status check
v9: switch to test_wait_pre_dump(_ack)

Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/transition/Makefile

@@ -21,6 +21,7 @@ TST_NOFILE	=	\
 		socket-tcp6     \
 		shmem		\
 		lazy-thp	\
+		pid_reuse	\
 
 
 TST_FILE	=	\

test/zdtm/transition/pid_reuse.c

@@ -0,0 +1,116 @@
+#include <fcntl.h>
+#include <sys/wait.h>
+#include <sys/mman.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Tests that forking tasks with same pid does not break iterative dump";
+const char *test_author = "Pavel Tikhomirov <ptikhomirov@virtuozzo.com>";
+
+enum {
+	VALUE_A = 1,
+	VALUE_B = 2,
+};
+
+#define CHILD_NS_PID 11235
+
+static int set_ns_next_pid(pid_t pid)
+{
+	char buf[32];
+	int len, fd;
+
+	fd = open("/proc/sys/kernel/ns_last_pid", O_WRONLY);
+	if (fd < 0) {
+		pr_perror("Failed to open ns_last_pid");
+		return -1;
+	}
+
+	len = snprintf(buf, sizeof(buf), "%d", pid - 1);
+	len -= write(fd, buf, len);
+	if (len)
+		pr_perror("Can't set ns_last_pid");
+	close(fd);
+
+	return len ? -1 : 0;
+}
+
+int main(int argc, char **argv)
+{
+	int pid, wpid, status;
+	bool overwrite = true;
+	bool wait = true;
+	int *variable;
+	void *mem;
+
+	test_init(argc, argv);
+
+	mem = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+	if (mem == MAP_FAILED) {
+		pr_perror("Can't mmap memory region");
+		return 1;
+	}
+
+	variable = (int *)mem;
+	*variable = VALUE_A;
+
+	test_daemon();
+
+	while (wait) {
+		if (set_ns_next_pid(CHILD_NS_PID))
+			return 1;
+
+		pid = fork();
+		if (pid == -1) {
+			pr_perror("fork");
+			return 1;
+		} else if (pid == 0) {
+			if (overwrite)
+				*variable = VALUE_B;
+
+			/* Reuse test_waitsig to wait SIGTERM from parent */
+			test_waitsig();
+
+			if (*variable != (overwrite ? VALUE_B : VALUE_A)) {
+				pr_err("Wrong value in a variable after restore\n");
+				exit(1);
+			}
+			exit(0);
+		}
+
+		if (pid != CHILD_NS_PID) {
+			pr_err("Child started with wrong pid %d (expected %d)\n", pid, CHILD_NS_PID);
+			kill(pid, SIGKILL);
+			waitpid(pid, NULL, 0);
+			return 1;
+		}
+
+		/* Notify we are ready for a next pre-dump/dump */
+		if (!overwrite)
+			test_wait_pre_dump_ack();
+
+		/* Wait for next pre-dump/dump finish */
+		if (test_wait_pre_dump())
+			wait = false;
+
+		if (kill(pid, SIGTERM)) {
+			pr_perror("kill");
+			return 1;
+		}
+
+		wpid = waitpid(pid, &status, 0);
+		if (wpid <= 0) {
+			pr_perror("waitpid");
+			return 1;
+		}
+
+		if (status) {
+			fail("Task %d died with exit status %x", wpid, status);
+			return 1;
+		}
+
+		overwrite = false;
+	}
+
+	pass();
+	return 0;
+}

test/zdtm/transition/pid_reuse.desc

@@ -0,0 +1 @@
+{'flags': 'suid pre-dump-notify'}