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    SubjectRe: [PATCH 2/2] devscgroup: relax task to dev_cgroup conversion
    Paul Menage wrote:
    > 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?

    Well... Maybe. I'll make a 3rd patch a bit later.
    I'm now testing RCU-protected whitelists.

    > 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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