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cgroups: relax ns_can_attach checks to allow attaching to grandchild cgroups

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The ns_proxy cgroup allows moving processes to child cgroups only one
level deep at a time.  This commit relaxes this restriction and makes it
possible to attach tasks directly to grandchild cgroups, e.g.:

($pid is in the root cgroup)
echo $pid > /cgroup/CG1/CG2/tasks

Previously this operation would fail with -EPERM and would have to be
performed as two steps:
echo $pid > /cgroup/CG1/tasks
echo $pid > /cgroup/CG1/CG2/tasks

Also, the target cgroup no longer needs to be empty to move a task there.

Signed-off-by: Grzegorz Nosek <root@localdomain.pl>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Grzegorz Nosek
2009-04-02 16:57:23 -07:00
committed by Linus Torvalds
parent d20a390a0e
commit 313e924c08
3 changed files with 12 additions and 17 deletions
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14
kernel/ns_cgroup.c
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@@ -34,7 +34,7 @@ int ns_cgroup_clone(struct task_struct *task, struct pid *pid)
/*
* Rules:
* 1. you can only enter a cgroup which is a child of your current
* 1. you can only enter a cgroup which is a descendant of your current
* cgroup
* 2. you can only place another process into a cgroup if
* a. you have CAP_SYS_ADMIN
@@ -45,21 +45,15 @@ int ns_cgroup_clone(struct task_struct *task, struct pid *pid)
static int ns_can_attach(struct cgroup_subsys *ss,
struct cgroup *new_cgroup, struct task_struct *task)
{
struct cgroup *orig;
if (current != task) {
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!cgroup_is_descendant(new_cgroup))
if (!cgroup_is_descendant(new_cgroup, current))
return -EPERM;
}
if (atomic_read(&new_cgroup->count) != 0)
return -EPERM;
orig = task_cgroup(task, ns_subsys_id);
if (orig && orig != new_cgroup->parent)
if (!cgroup_is_descendant(new_cgroup, task))
return -EPERM;
return 0;
@@ -77,7 +71,7 @@ static struct cgroup_subsys_state *ns_create(struct cgroup_subsys *ss,
if (!capable(CAP_SYS_ADMIN))
return ERR_PTR(-EPERM);
if (!cgroup_is_descendant(cgroup))
if (!cgroup_is_descendant(cgroup, current))
return ERR_PTR(-EPERM);
ns_cgroup = kzalloc(sizeof(*ns_cgroup), GFP_KERNEL);