[BUG?] fsconfig restart_syscall failed

[Cai Xinchen]

Hello:
  I am doing some test for kernel 6.4, util-linux version:2.39.1.
Have you encountered similar problems? If there is a fix, please
let me know.
Thank you very much

--------------------------------------------------

util-linux version 2.39.1 call mount use fsopen->fsconfig->fsmount->close
instead of mount syscall.

And use this shell test:

#!/bin/bash
mkdir -p /tmp/cgroup/cgrouptest
while true
do
        mount -t cgroup -o none,name=foo cgroup /tmp/cgroup/cgrouptest
        ret=$?
        if [ $ret -ne 0 ];then
                echo "mount failed , $ret"
        fi
        umount /tmp/cgroup/cgrouptest
        ret=$?
        if [ $ret -ne 0 ];then
                echo "umount failed, $ret"
        fi
done

And as a result, we mount cgroup immediately after umount, it will return
failed.

in fsconfig syscall, we find this stack:

SYSCALL_DEFINE5(fsconfig, ...)
        vfs_fsconfig_locked
                if (fc->phase != FS_CONTEXT_CREATE_PARAMS)
                        return -EBUSY;

                vfs_get_tree
                        fc->ops->get_tree // cgroup1_get_tree
                                if (!ret && !percpu_ref_tryget_live
(&ctx->root->cgrp.self.refcnt))
                                        ret = 1;
                                ...
                                if (unlikely(ret > 0)) {
                                        msleep(10);
                                        restart_syscall();
                                }
                ...
                fc->phase = FS_CONTEXT_FAILED;

in mount syscall, no function will check fs->phase, and fc is recreate
in monnt syscall. However, in fdconfig syscall, fc->phase is not initial as
FS_CONTEXT_CREATE_PARAMS, restart_syscall will return -EBUSY. fc is created
in fsopen syscall.