# Re: \[PATCH 02/12\] container quota: lock/unlock mount namespace when performing quotactl.

- From: Glauber Costa \<hidden\>
- Date: 2012-05-31 09:04:24 
- List: cgroups
- Page: https://ratatoskr.run/cgroups/2012/05/64683
- Thread: https://ratatoskr.run/cgroups/2012/05/64683/t.md

```text
On 05/30/2012 06:58 PM, jeff.liu-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org wrote:
> Introduce two functions to lock/unlock a particular mount namespace
> when container quota operations is performed.
>
> Signed-off-by: Jie Liu<redacted>
> ---
>   fs/namespace.c                |   17 +++++++++++++++++
>   include/linux/mnt_namespace.h |   13 +++++++++++++
>   2 files changed, 30 insertions(+), 0 deletions(-)
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index e608199..8823ba8 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2633,3 +2633,20 @@ bool our_mnt(struct vfsmount *mnt)
>   {
>   	return check_mnt(real_mount(mnt));
>   }
> +
> +/*
> + * Lock the mount namespace when performing a particular container
> + * disk quotactl operation, especially to protect removing it.
> + */
> +void lock_mnt_ns(struct mnt_namespace *ns)
> +{
> +	down_write(&namespace_sem);
> +}
> +
> +/*
> + * Unlock the mount namespace after quotactl on that was done.
> + */
> +void unlock_mnt_ns(struct mnt_namespace *ns)
> +{
> +	up_write(&namespace_sem);
> +}
> diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
> index 5a8e390..ff72ed5 100644
> --- a/include/linux/mnt_namespace.h
> +++ b/include/linux/mnt_namespace.h
> @@ -9,6 +9,19 @@ extern struct mnt_namespace *copy_mnt_ns(unsigned long, struct mnt_namespace *,
>   		struct fs_struct *);
>   extern void put_mnt_ns(struct mnt_namespace *ns);
>
> +#ifdef CONFIG_NS_QUOTA
> +extern void lock_mnt_ns(struct mnt_namespace *);
> +extern void unlock_mnt_ns(struct mnt_namespace *);
> +#else
> +void lock_mnt_ns(struct mnt_namespace *)
> +{
> +}
> +
> +void unlock_mnt_ns(struct mnt_namespace *)
> +{
> +}
> +#endif
> +

Seems weird. There is nothing ns-quota specific in locking a namespace.
Also, just grabbing a lock from an outer subsystem is quite ugly. If you are grabbing a namespace lock, this suggests you are tweaking namespace data. So you should have that file provide you with a function that does the full operation.

Of course there are exceptions to that, but it rings a bell.
```