linux-kernel - Re: [PATCH 2/2] devscgroup: relax task to dev

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Date:	Wed, 4 Jun 2008 02:20:02 -0700
From:	"Paul Menage" <menage@...gle.com>
To:	"Pavel Emelyanov" <xemul@...nvz.org>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Serge Hallyn" <serue@...ibm.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] devscgroup: relax task to dev_cgroup conversion

On Wed, Jun 4, 2008 at 12:39 AM, Pavel Emelyanov <xemul@...nvz.org> wrote:
> Two functions, that need to get a device_cgroup from a task (they
> are devcgroup_inode_permission and devcgroup_inode_mknod) make it
> in a strange way:
>
> They get a css_set from task, then a subsys_state from css_set,
> then a cgroup from the state and then a subsys_state again from
> the cgroup. Besides, the devices_subsys_id is read from memory,
> whilst there's a enum-ed constant for it.
>
> Optimize this part a bit:
> 1. Get the subsys_stats form the task and be done - no 2 extra
>   dereferences,
> 2. Use the device_subsys_id constant, not the value from memory
>   (i.e. one less dereference).
>
> Found while preparing 2.6.26 OpenVZ port.
>
> Signed-off-by: Pavel Emelyanov <xemul@...nvz.org>

Acked-by: Paul Menage <menage@...gle.com>

Yes, that's more how the css_set pointers are meant to be used. Maybe
improve it further by extracting a task_to_devcgroup() inline
function?

Paul

>
> ---
>  security/device_cgroup.c |   10 ++++------
>  1 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 15f2f80..f9941a7 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -506,7 +506,6 @@ struct cgroup_subsys devices_subsys = {
>
>  int devcgroup_inode_permission(struct inode *inode, int mask)
>  {
> -       struct cgroup *cgroup;
>        struct dev_cgroup *dev_cgroup;
>        struct dev_whitelist_item *wh;
>
> @@ -515,8 +514,8 @@ int devcgroup_inode_permission(struct inode *inode, int mask)
>                return 0;
>        if (!S_ISBLK(inode->i_mode) && !S_ISCHR(inode->i_mode))
>                return 0;
> -       cgroup = task_cgroup(current, devices_subsys.subsys_id);
> -       dev_cgroup = cgroup_to_devcgroup(cgroup);
> +       dev_cgroup = css_to_devcgroup(task_subsys_state(current,
> +                               devices_subsys_id));
>        if (!dev_cgroup)
>                return 0;
>
> @@ -547,12 +546,11 @@ acc_check:
>
>  int devcgroup_inode_mknod(int mode, dev_t dev)
>  {
> -       struct cgroup *cgroup;
>        struct dev_cgroup *dev_cgroup;
>        struct dev_whitelist_item *wh;
>
> -       cgroup = task_cgroup(current, devices_subsys.subsys_id);
> -       dev_cgroup = cgroup_to_devcgroup(cgroup);
> +       dev_cgroup = css_to_devcgroup(task_subsys_state(current,
> +                               devices_subsys_id));
>        if (!dev_cgroup)
>                return 0;
>
> --
> 1.5.3.4
>
>
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