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Commit a8638030 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: add cgroup_subsys->post_create() 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarMichal Hocko <mhocko@suse.cz>
Reviewed-by: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Cc: Glauber Costa <glommer@parallels.com>
parent 316eb661

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -438,6 +438,7 @@ int cgroup_taskset_size(struct cgroup_taskset *tset); 


struct cgroup_subsys {

	struct cgroup_subsys_state *(*create)(struct cgroup *cgrp);

	void (*post_create)(struct cgroup *cgrp);

	void (*pre_destroy)(struct cgroup *cgrp);

	void (*destroy)(struct cgroup *cgrp);

	int (*can_attach)(struct cgroup *cgrp, struct cgroup_taskset *tset);

kernel/cgroup.c

+13 −2
Original line number Diff line number Diff line
@@ -4059,10 +4059,15 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, 
	if (err < 0)

		goto err_remove;



	for_each_subsys(root, ss) {

		/* each css holds a ref to the cgroup's dentry */

	for_each_subsys(root, ss)

		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;