seize: enable support for frozen containers

Container runtimes like CRI-O and containerd utilize the freezer cgroup
to create a consistent snapshot of container rootfs changes. In this
case, the container is frozen before invoking CRIU. Once CRIU
successfully completes, a copy of the container rootfs diff is saved,
and then the container is unfrozen. To enable GPU checkpointing support
with these runtimes, we need to unfreeze the cgroup and restore it to
its original state at the end.

Fixes: #2508

Signed-off-by: Radostin Stoyanov <rstoyanov@fedoraproject.org>

criu/seize.c

@@ -509,6 +509,7 @@ static int check_freezer_cgroup(void)
 {
 	enum freezer_state state = THAWED;
 	int fd;
+	int exit_code = -1;
 
 	BUG_ON(!freeze_cgroup_disabled);
 
@@ -517,17 +518,22 @@ static int check_freezer_cgroup(void)
 		return -1;
 
 	state = get_freezer_state(fd);
-	close(fd);
 	if (state == FREEZER_ERROR) {
-		return -1;
+		goto err;
 	}
 
+	origin_freezer_state = state == FREEZING ? FROZEN : state;
+
 	if (state != THAWED) {
-		pr_err("One or more plugins are incompatible with the freezer cgroup in the FROZEN state.\n");
-		return -1;
+		pr_warn("unfreezing cgroup for plugin compatibility\n");
+		if (freezer_write_state(fd, THAWED))
+			goto err;
 	}
 
-	return 0;
+	exit_code = 0;
+err:
+	close(fd);
+	return exit_code;
 }
 
 static int freeze_processes(void)