Quoting a...@redhat.com (a...@redhat.com):
> Allocate resources and change behavior only when online. This is needed in
> order to determine if a node is suitable for hierarchy propagation or if it's
> being removed.
>
> Locking:
> Both functions take devcgroup_mutex to make changes to device_cgroup
> structure.
> Hierarchy propagation will also take devcgroup_mutex before walking the
> tree while walking the tree itself is protected by rcu lock.
>
> Acked-by: Tejun Heo <t...@kernel.org>
> Cc: Tejun Heo <t...@kernel.org>
> Cc: Serge Hallyn <serge.hal...@canonical.com>
Acked-by: Serge Hallyn <serge.hal...@canonical.com>
> Signed-off-by: Aristeu Rozanski <a...@redhat.com>
>
> ---
> security/device_cgroup.c | 59
> +++++++++++++++++++++++++++++++++--------------
> 1 file changed, 42 insertions(+), 17 deletions(-)
>
> --- github.orig/security/device_cgroup.c 2013-01-30 09:00:09.435351867
> -0500
> +++ github/security/device_cgroup.c 2013-01-30 09:09:12.572464122 -0500
> @@ -230,14 +230,51 @@ static void dev_exception_clean(struct d
> __dev_exception_clean(dev_cgroup);
> }
>
> +/**
> + * devcgroup_online - initializes devcgroup's behavior and exceptions based
> on
> + * parent's
> + * @cgroup: cgroup getting online
> + * returns 0 in case of success, error code otherwise
> + */
> +static int devcgroup_online(struct cgroup *cgroup)
> +{
> + struct dev_cgroup *dev_cgroup, *parent_dev_cgroup = NULL;
> + int ret = 0;
> +
> + mutex_lock(&devcgroup_mutex);
> + dev_cgroup = cgroup_to_devcgroup(cgroup);
> + if (cgroup->parent)
> + parent_dev_cgroup = cgroup_to_devcgroup(cgroup->parent);
> +
> + if (parent_dev_cgroup == NULL)
> + dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
> + else {
> + ret = dev_exceptions_copy(&dev_cgroup->exceptions,
> + &parent_dev_cgroup->exceptions);
> + if (!ret)
> + dev_cgroup->behavior = parent_dev_cgroup->behavior;
> + }
> + mutex_unlock(&devcgroup_mutex);
> +
> + return ret;
> +}
> +
> +static void devcgroup_offline(struct cgroup *cgroup)
> +{
> + struct dev_cgroup *dev_cgroup = cgroup_to_devcgroup(cgroup);
> +
> + mutex_lock(&devcgroup_mutex);
> + dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
> + mutex_unlock(&devcgroup_mutex);
> +}
> +
> /*
> * called from kernel/cgroup.c with cgroup_lock() held.
> */
> static struct cgroup_subsys_state *devcgroup_css_alloc(struct cgroup *cgroup)
> {
> - struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
> + struct dev_cgroup *dev_cgroup;
> struct cgroup *parent_cgroup;
> - int ret;
>
> dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
> if (!dev_cgroup)
> @@ -245,23 +282,9 @@ static struct cgroup_subsys_state *devcg
> INIT_LIST_HEAD(&dev_cgroup->exceptions);
> INIT_LIST_HEAD(&dev_cgroup->local.exceptions);
> dev_cgroup->local.behavior = DEVCG_DEFAULT_NONE;
> + dev_cgroup->behavior = DEVCG_DEFAULT_NONE;
> parent_cgroup = cgroup->parent;
>
> - if (parent_cgroup == NULL)
> - dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
> - else {
> - parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
> - mutex_lock(&devcgroup_mutex);
> - ret = dev_exceptions_copy(&dev_cgroup->exceptions,
> - &parent_dev_cgroup->exceptions);
> - dev_cgroup->behavior = parent_dev_cgroup->behavior;
> - mutex_unlock(&devcgroup_mutex);
> - if (ret) {
> - kfree(dev_cgroup);
> - return ERR_PTR(ret);
> - }
> - }
> -
> return &dev_cgroup->css;
> }
>
> @@ -635,6 +658,8 @@ struct cgroup_subsys devices_subsys = {
> .can_attach = devcgroup_can_attach,
> .css_alloc = devcgroup_css_alloc,
> .css_free = devcgroup_css_free,
> + .css_online = devcgroup_online,
> + .css_offline = devcgroup_offline,
> .subsys_id = devices_subsys_id,
> .base_cftypes = dev_cgroup_files,
>
>
> --
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