linux-kernel - Re: [BUG?] fsconfig restart

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Date:   Fri, 22 Sep 2023 10:08:36 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Cai Xinchen <caixinchen1@...wei.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, dhowells@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG?] fsconfig restart_syscall failed

On Fri, Sep 22, 2023 at 10:18:24AM +0800, Cai Xinchen wrote:
> 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


> 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.

Mount api system calls aren't restartable so that doesn't work. cgroup2
doesn't have this issue, only cgroup1 has. So cgroup1_get_tree() should
probably be fixed if anyone cares.