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SubjectRe: [PATCH 2/2] devscgroup: relax task to dev_cgroup conversion
On Wed, Jun 4, 2008 at 12:39 AM, Pavel Emelyanov <xemul@openvz.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@openvz.org>

Acked-by: Paul Menage <menage@google.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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