cow01: try to read a page to take it from a swap

Vladimir said that a page can be unmapped from one process, but can be
mmaped in another one. In this case we can't understand whether both
processes link to the same page or they don't.

So we can try read both pages to take them from swap.

Cc: Vladimir Davydov <vdavydov@parallels.com>
Reported-by: Parallels' QA
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm/live/static/cow01.c

@@ -8,6 +8,7 @@
 #include <linux/limits.h>
 #include <sys/user.h>
 #include <stdlib.h>
+#include <sys/socket.h>
 
 #include "zdtmtst.h"
 
@@ -55,12 +56,12 @@ static pid_t child_pid;
  * file, etc.).  A return code of 1 means failure, it means criu was not able
  * to checkpoint and/or restore the process properly.
  */
-#define EXECUTE_ACTION(func) ({		\
+#define EXECUTE_ACTION(func, fd) ({	\
 	int __ret = 0;			\
-	__ret |= func(&sep_tcs);	\
-	__ret |= func(&cow_tcs);	\
-	__ret |= func(&cow_gd_tcs);	\
-	__ret |= func(&file_tcs);	\
+	__ret |= func(&sep_tcs, fd);	\
+	__ret |= func(&cow_tcs, fd);	\
+	__ret |= func(&cow_gd_tcs, fd);	\
+	__ret |= func(&file_tcs, fd);	\
 	__ret;				\
 })
 
@@ -72,7 +73,7 @@ struct test_cases cow_tcs = {.init = init_cow, .tname = "cow_tcs"},
 uint32_t zero_crc = ~1;
 
 static int is_cow(void *addr, pid_t pid_child, pid_t pid_parent,
-		  uint64_t *map_child_ret, uint64_t *map_parent_ret)
+		  uint64_t *map_child_ret, uint64_t *map_parent_ret, int fd)
 {
 	char buf[PATH_MAX];
 	unsigned long pfn = (unsigned long) addr / PAGE_SIZE;
@@ -99,6 +100,8 @@ static int is_cow(void *addr, pid_t pid_child, pid_t pid_parent,
 	 * so we should do several iterations.
 	 */
 	for (i = 0; i < 10; i++) {
+		void **p = addr;
+
 		lseek_ret = lseek(fd_child, pfn * sizeof(map_child), SEEK_SET);
 		if (lseek_ret == (off_t) -1) {
 			err("Unable to seek child pagemap to virtual addr %#08lx",
@@ -127,8 +130,20 @@ static int is_cow(void *addr, pid_t pid_child, pid_t pid_parent,
 			return -1;
 		}
 
-		if (map_child == map_parent)
+		if (map_child == map_parent && i > 5)
 			break;
+
+		p = (void **)(addr + i * PAGE_SIZE);
+		test_msg("Read *%p = %p\n", p, p[0]);
+		if (write(fd, &p, sizeof(p)) != sizeof(p)) {
+			err("write");
+			return -1;
+		}
+		if (read(fd, &p, sizeof(p)) != sizeof(p)) {
+			err("read");
+			return -1;
+		}
+		test_msg("Child %p\n", p);
 	}
 
 	close(fd_child);
@@ -143,7 +158,7 @@ static int is_cow(void *addr, pid_t pid_child, pid_t pid_parent,
 	return map_child != map_parent;
 }
 
-static int child_prep(struct test_cases *test_cases)
+static int child_prep(struct test_cases *test_cases, int fd)
 {
 	int i;
 	uint8_t *addr = test_cases->addr;
@@ -164,7 +179,7 @@ static int child_prep(struct test_cases *test_cases)
 	return 0;
 }
 
-static int child_check(struct test_cases *test_cases)
+static int child_check(struct test_cases *test_cases, int fd)
 {
 	int i, ret = 0;
 	uint8_t *addr = test_cases->addr;
@@ -185,7 +200,7 @@ static int child_check(struct test_cases *test_cases)
 	return ret;
 }
 
-static int parent_before_fork(struct test_cases *test_cases)
+static int parent_before_fork(struct test_cases *test_cases, int fd)
 {
 	uint8_t *addr;
 	int i;
@@ -215,7 +230,7 @@ static int parent_before_fork(struct test_cases *test_cases)
 	return 0;
 }
 
-static int parent_post_fork(struct test_cases *test_cases)
+static int parent_post_fork(struct test_cases *test_cases, int fd)
 {
 	uint8_t *addr = test_cases->addr;
 	int i;
@@ -238,7 +253,7 @@ static int parent_post_fork(struct test_cases *test_cases)
 	return 0;
 }
 
-static int parent_check(struct test_cases *test_cases)
+static int parent_check(struct test_cases *test_cases, int fd)
 {
 	uint8_t *addr = test_cases->addr;
 	int i, ret = 0;
@@ -265,7 +280,7 @@ static int parent_check(struct test_cases *test_cases)
 			int is_cow_ret;
 
 			is_cow_ret = is_cow(addr + i * PAGE_SIZE, child_pid, getpid(),
-					    &map_child, &map_parent);
+					    &map_child, &map_parent, fd);
 			ret |= is_cow_ret;
 			if (is_cow_ret == 1) {
 				errno = 0;
@@ -387,7 +402,7 @@ static int init_file(struct test_cases *tcs)
 	return 0;
 }
 
-static int child(task_waiter_t *child_waiter)
+static int child(task_waiter_t *child_waiter, int fd)
 {
 	int ret = 0;
 
@@ -399,13 +414,29 @@ static int child(task_waiter_t *child_waiter)
 		return -1;
 	}
 
-	EXECUTE_ACTION(child_prep);
+	EXECUTE_ACTION(child_prep, fd);
 
 	task_waiter_complete_current(child_waiter);
 
-	test_waitsig();
+	while (1) {
+		void **p;
+		ret = read(fd, &p, sizeof(p));
+		if (ret == 0)
+			break;
+		if (ret != sizeof(p)) {
+			err("read");
+			return -1;
+		}
+		test_msg("Read *%p = %p\n", p, p[0]);
+		p = ((void **)p)[0];
+		if (write(fd, &p, sizeof(p)) != sizeof(p)) {
+			err("write");
+			return -1;
+		}
+		ret = 0;
+	}
 
-	ret |= EXECUTE_ACTION(child_check);
+	ret = EXECUTE_ACTION(child_check, fd);
 
 	// Exit code of child process, so return 2 for a test error, 1 for a
 	// test failure (child_check got mismatched checksums) and 0 for
@@ -416,8 +447,9 @@ static int child(task_waiter_t *child_waiter)
 int main(int argc, char ** argv)
 {
 	uint8_t zero_page[PAGE_SIZE];
-	int status, ret = 0;
+	int status = -1, ret = 0;
 	task_waiter_t child_waiter;
+	int pfd[2], fd;
 
 	task_waiter_init(&child_waiter);
 
@@ -427,7 +459,12 @@ int main(int argc, char ** argv)
 
 	test_init(argc, argv);
 
-	if (EXECUTE_ACTION(parent_before_fork))
+	if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, pfd)) {
+		err("pipe");
+		return 1;
+	}
+
+	if (EXECUTE_ACTION(parent_before_fork, -1))
 		return 2;
 
 	child_pid = test_fork();
@@ -436,20 +473,24 @@ int main(int argc, char ** argv)
 		return 2;
 	}
 
-	if (child_pid == 0)
-		return child(&child_waiter);
+	if (child_pid == 0) {
+		close(pfd[0]);
+		return child(&child_waiter, pfd[1]);
+	}
+	close(pfd[1]);
+	fd = pfd[0];
 
 	task_waiter_wait4(&child_waiter, child_pid);
 
-	EXECUTE_ACTION(parent_post_fork);
+	EXECUTE_ACTION(parent_post_fork, -1);
 
 	test_daemon();
 
 	test_waitsig();
 
-	ret |= EXECUTE_ACTION(parent_check);
+	ret |= EXECUTE_ACTION(parent_check, fd);
 
-	kill(child_pid, SIGTERM);
+	close(fd);
 	wait(&status);
 
 	unlink(filename);