save-restore/CRIU

Hi everyone, I am debugging a failed test in my cgroup-v2 PR. In global properties, we use access(path, F_OK) if errno == ENOENT, we simply skip this global property. However, I observe that in the failed test the errno of access(path, F_OK) is EACCESS but when opening the file the errno is ENOENT which is weird to me. I also see some access(path, F_OK) returns EACCESS but can still open and read that file.
My patch for getting some logs

diff --git a/criu/cgroup.c b/criu/cgroup.c
index 2cdb63609..f4f50fd38 100644
--- a/criu/cgroup.c
+++ b/criu/cgroup.c
@@ -382,14 +382,19 @@ static int dump_cg_props_array(const char *fpath, struct cgroup_dir *ncd, const
        struct cgroup_prop *prop;

        for (j = 0; cgp && j < cgp->nr_props; j++) {
+               int ret;
+
                if (snprintf(buf, PATH_MAX, "%s/%s", fpath, cgp->props[j]) >= PATH_MAX) {
                        pr_err("snprintf output was truncated\n");
                        return -1;
                }

-               if (access(buf, F_OK) < 0 && errno == ENOENT) {
+               ret = access(buf, F_OK);
+               if (ret < 0 && errno == ENOENT) {
                        pr_info("Couldn't open %s. This cgroup property may not exist on this kernel\n", buf);
                        continue;
+               } else if (ret < 0) {
+                       pr_perror("cgroup: Path: %s", buf);
                }

                prop = create_cgroup_prop(cgp->props[j]);

Error log

(00.071032) Error (criu/cgroup.c:397): cg: cgroup: Path: /proc/self/fd/16/bar/cgroup.clone_children: Permission denied
(00.071045) cg: Dumping value 0 from /proc/self/fd/16/bar/cgroup.clone_children
(00.071049) Error (criu/cgroup.c:397): cg: cgroup: Path: /proc/self/fd/16/bar/notify_on_release: Permission denied
(00.071056) cg: Dumping value 0 from /proc/self/fd/16/bar/notify_on_release
(00.071060) Error (criu/cgroup.c:397): cg: cgroup: Path: /proc/self/fd/16/bar/cgroup.procs: Permission denied
(00.071066) cg: Dumping value  from /proc/self/fd/16/bar/cgroup.procs
(00.071069) Error (criu/cgroup.c:397): cg: cgroup: Path: /proc/self/fd/16/bar/tasks: Permission denied
(00.071075) cg: Dumping value  from /proc/self/fd/16/bar/tasks
(00.071079) Error (criu/cgroup.c:397): cg: cgroup: Path: /proc/self/fd/16/bar/cgroup.subtree_control: Permission denied
(00.071084) Error (criu/cgroup.c:292): cg: Failed opening /proc/self/fd/16/bar/cgroup.subtree_control: No such file or directory
(00.071085) Error (criu/cgroup.c:462): cg: dumping global properties failed
(00.071088) Error (criu/cgroup.c:732): cg: failed walking /proc/self/fd/16/ for empty cgroups: No such file or directory