[Devel] [PATCH VZ8 v2 14/14] cgroup/ve: do not run release_agent on non-running ve

[Kirill Tkhai]

On 10.02.2021 13:03, Valeriy Vdovin wrote:
> cgroup1_release_agent is a function that runs within a private ve workqueue.
> When executed, it runs an executable in a userspace by a call to 
> call_usermodehelper_ve. There is conflict that when ve is getting shutdown and
> some of last cgroups get's deleted at the same time, the workqueue might still
> be running, but ve_stop_ns has already been called. ve_stop_ns will stop
> usermode helper threads, needed for call_usermodehelper_ve. Because of that a
> call to call_usermodehelper_ve will never return, causing a hang.  To defeat
> that hang VZ7 code of call_usermodehelper_ve included the check that ve is
> still running before running the userspace executable.
> It also checked for ve->init_task->flags & PF_EXITING condition. But in VZ8 the
> whole usermodehelper infrastructure is much more different. Also VZ8 does not
> have ve->init_task in it's fields. That is why it seems more relevant right now
> to do ve->is_running check before the call to call_usermodehelper_ve.
> 
> Signed-off-by: Valeriy Vdovin <valeriy.vdovin at virtuozzo.com>
> ---
>  kernel/cgroup/cgroup-v1.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
> index 993ac38b895f..2521d2727b42 100644
> --- a/kernel/cgroup/cgroup-v1.c
> +++ b/kernel/cgroup/cgroup-v1.c
> @@ -937,6 +937,13 @@ void cgroup1_release_agent(struct work_struct *work)
>  
>  		mutex_unlock(&cgroup_mutex);
>  
> +		down_write(&ve->op_sem);
> +		if (!ve->is_running) {
> +			up_write(&ve->op_sem);
> +			mutex_lock(&cgroup_mutex);

Below in this function you already have up_write+mutex_lock. Just goto there.

> +			goto continue_free;
> +		}
> +
>  		err = call_usermodehelper_ve(ve, argv[0], argv,
>  			envp, UMH_WAIT_EXEC);
>  
>