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    Subject[PATCH 2/2] devscgroup: relax task to dev_cgroup conversion
    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>

    ---
    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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