cgroup: add cgroup_subsys->post_create() (a8638030) · Commits · 戴 / test

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 <tj@kernel.org> Acked-by:

Michal Hocko <mhocko@suse.cz> Reviewed-by:

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by:

Li Zefan <lizefan@huawei.com> Cc: Glauber Costa <glommer@parallels.com>

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;

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