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cgroup: add cgroup_subsys->post_create()

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Currently, there's no way for a controller to find out whether a new
cgroup finished all ->create() allocatinos successfully and is
considered "live" by cgroup.

This becomes a problem later when we add generic descendants walking
to cgroup which can be used by controllers as controllers don't have a
synchronization point where it can synchronize against new cgroups
appearing in such walks.

This patch adds ->post_create().  It's called after all ->create()
succeeded and the cgroup is linked into the generic cgroup hierarchy.
This plays the counterpart of ->pre_destroy().

When used in combination with the to-be-added generic descendant
iterators, ->post_create() can be used to implement reliable state
inheritance.  It will be explained with the descendant iterators.

v2: Added a paragraph about its future use w/ descendant iterators per
    Michal.

v3: Forgot to add ->post_create() invocation to cgroup_load_subsys().
    Fixed.

Signed-off-by: Tejun Heo <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Acked-by: Li Zefan <[email protected]>
Cc: Glauber Costa <[email protected]>
This commit is contained in:
Tejun Heo 2012-11-09 09:12:29 -08:00
commit a8638030f6
2 changed files with 14 additions and 2 deletions
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15
kernel/cgroup.c
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@ -4059,10 +4059,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
if (err < 0)
goto err_remove;
/* each css holds a ref to the cgroup's dentry */
for_each_subsys(root, ss)
for_each_subsys(root, ss) {
/* each css holds a ref to the cgroup's dentry */
dget(dentry);
/* creation succeeded, notify subsystems */
if (ss->post_create)
ss->post_create(cgrp);
}
/* The cgroup directory was pre-locked for us */
BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
@ -4280,6 +4285,9 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)
ss->active = 1;
if (ss->post_create)
ss->post_create(&ss->root->top_cgroup);
/* this function shouldn't be used with modular subsystems, since they
* need to register a subsys_id, among other things */
BUG_ON(ss->module);
@ -4389,6 +4397,9 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)
ss->active = 1;
if (ss->post_create)
ss->post_create(&ss->root->top_cgroup);
/* success! */
mutex_unlock(&cgroup_mutex);
return 0;