restore: restore freezer cgroup state

Issue checkpoint-restore#20. (Support C/R of frozen cgroup)

Patch restores freezer cgroup state between finalize_restore stages.
It should be done after first stage because we cannot unmap restorer blob
from frozen process, and before second stage because we must freeze processes
before they continue run.
We also need to move fini_cgroup between these stages to provide freezer
cgroup state restorer access to cgroup mount directories.
Error handlers contains fini_cgroup, so we are sure that fini_cgroup call
won't be missed.

Signed-off-by: Evgeniy Akimov <[email protected]>
Signed-off-by: Eugene Batalov <[email protected]>

Author: wtf42

cgroup.c

@@ -877,6 +877,76 @@ int dump_real_freezer_state(void)
 	return 0;
 }
 
+int restore_freezer_state(void)
+{
+	int fd, err, sfd, cgfd, i;
+	char state[8];
+	CgControllerEntry *freezer_ctrl = NULL;
+	char paux[PATH_MAX];
+	int ctrl_off;
+
+	sfd = get_service_fd(IMG_FD_OFF);
+	if (faccessat(sfd, freezer_state_file, F_OK, 0) < 0)
+		return 0;
+
+	fd = openat(sfd, freezer_state_file, O_RDONLY);
+	if (fd < 0) {
+		pr_err("Can't open freezer state dump file\n");
+		return -1;
+	}
+	err = read(fd, state, sizeof(state));
+	close(fd);
+	if (err < 0) {
+		pr_err("Can't load freezer state\n");
+		return -1;
+	}
+
+	if (strncmp(state, "FROZEN", sizeof("FROZEN") - 1) != 0)
+		return 0;
+
+	for (i = 0; i < n_controllers; i++) {
+		CgControllerEntry *ctrl = controllers[i];
+
+		if (cgroup_contains(ctrl->cnames, ctrl->n_cnames, "freezer")) {
+			freezer_ctrl = ctrl;
+			break;
+		}
+	}
+
+	if (!freezer_ctrl) {
+		pr_err("Can't restore freezer cgroup state: root freezer cgroup not found\n");
+		return -1;
+	}
+
+	/*
+	 * Here we rely on --freeze-cgroup option assumption that all tasks are in a
+	 * specified freezer group, so we need to freeze only one root freezer cgroup.
+	 */
+	BUG_ON(freezer_ctrl->n_dirs != 1);
+
+	cgfd = get_service_fd(CGROUP_YARD);
+	ctrl_off = ctrl_dir_and_opt(freezer_ctrl, paux, sizeof(paux), NULL, 0);
+
+	for (i = 0; i < freezer_ctrl->n_dirs; i++) {
+		CgroupDirEntry *entry = freezer_ctrl->dirs[i];
+
+		snprintf(paux + ctrl_off, sizeof(paux) - ctrl_off, "/%s/freezer.state", entry->dir_name);
+		fd = openat(cgfd, paux, O_WRONLY);
+		if (fd < 0) {
+			pr_err("Can't open %s\n", paux);
+			return -1;
+		}
+		err = write(fd, "FROZEN", sizeof("FROZEN"));
+		close(fd);
+		if (err < 0) {
+			pr_err("Can't update %s (%d)\n", paux, err);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
 static const char *special_cpuset_props[] = {
 	"cpuset.cpus",
 	"cpuset.mems",

cr-restore.c

@@ -1902,7 +1902,6 @@ static int restore_root_task(struct pstree_item *init)
 		goto out_kill;
 
 	ret = prepare_cgroup_properties();
-	fini_cgroup();
 	if (ret < 0)
 		goto out_kill;
 
@@ -1945,8 +1944,11 @@ static int restore_root_task(struct pstree_item *init)
 	if (clear_breakpoints())
 		pr_err("Unable to flush breakpoints\n");
 
-	if (ret == 0)
+	if (ret == 0) {
 		finalize_restore();
+		ret = restore_freezer_state();
+	}
+	fini_cgroup();
 
 	/* Detaches from processes and they continue run through sigreturn. */
 	finalize_restore_detach(ret);

include/cgroup.h

@@ -12,6 +12,7 @@ int prepare_cgroup_properties(void);
 void fini_cgroup(void);
 
 int dump_real_freezer_state(void);
+int restore_freezer_state(void);
 
 struct cg_controller;