Commit a31f2d3f authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: introduce CSS_ONLINE flag and on/offline_css() helpers 



New helpers on/offline_css() respectively wrap ->post_create() and
->pre_destroy() invocations.  online_css() sets CSS_ONLINE after
->post_create() is complete and offline_css() invokes ->pre_destroy()
iff CSS_ONLINE is set and clears it while also handling the temporary
dropping of cgroup_mutex.

This patch doesn't introduce any behavior change at the moment but
will be used to improve cgroup_create() failure path and allow
->post_create() to fail.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 42809dd4

include/linux/cgroup.h

+1 −0
Original line number Diff line number Diff line
@@ -82,6 +82,7 @@ struct cgroup_subsys_state { 
/* bits in struct cgroup_subsys_state flags field */

enum {

	CSS_ROOT	= (1 << 0), /* this CSS is the root of the subsystem */

	CSS_ONLINE	= (1 << 1), /* between ->post_create() and ->pre_destroy() */

};



/* Caller must verify that the css is not for root cgroup */

kernel/cgroup.c

+42 −23
Original line number Diff line number Diff line
@@ -4035,6 +4035,42 @@ static void init_cgroup_css(struct cgroup_subsys_state *css, 
	INIT_WORK(&css->dput_work, css_dput_fn);

}



/* invoke ->post_create() on a new CSS and mark it online */

static void online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)

{

	lockdep_assert_held(&cgroup_mutex);



	if (ss->post_create)

		ss->post_create(cgrp);

	cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;

}



/* if the CSS is online, invoke ->pre_destory() on it and mark it offline */

static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)

	__releases(&cgroup_mutex) __acquires(&cgroup_mutex)

{

	struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];



	lockdep_assert_held(&cgroup_mutex);



	if (!(css->flags & CSS_ONLINE))

		return;



	/*

	 * pre_destroy() should be called with cgroup_mutex unlocked.  See

	 * 3fa59dfbc3 ("cgroup: fix potential deadlock in pre_destroy") for

	 * details.  This temporary unlocking should go away once

	 * cgroup_mutex is unexported from controllers.

	 */

	if (ss->pre_destroy) {

		mutex_unlock(&cgroup_mutex);

		ss->pre_destroy(cgrp);

		mutex_lock(&cgroup_mutex);

	}



	cgrp->subsys[ss->subsys_id]->flags &= ~CSS_ONLINE;

}



/*

 * cgroup_create - create a cgroup

 * @parent: cgroup that will be parent of the new cgroup
@@ -4137,8 +4173,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, 
		dget(dentry);



		/* creation succeeded, notify subsystems */

		if (ss->post_create)

			ss->post_create(cgrp);

		online_css(ss, cgrp);

	}



	err = cgroup_populate_dir(cgrp, true, root->subsys_mask);
@@ -4240,18 +4275,9 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	}

	set_bit(CGRP_REMOVED, &cgrp->flags);



	/*

	 * Tell subsystems to initate destruction.  pre_destroy() should be

	 * called with cgroup_mutex unlocked.  See 3fa59dfbc3 ("cgroup: fix

	 * potential deadlock in pre_destroy") for details.  This temporary

	 * unlocking should go away once cgroup_mutex is unexported from

	 * controllers.

	 */

	mutex_unlock(&cgroup_mutex);

	/* tell subsystems to initate destruction */

	for_each_subsys(cgrp->root, ss)

		if (ss->pre_destroy)

			ss->pre_destroy(cgrp);

	mutex_lock(&cgroup_mutex);

		offline_css(ss, cgrp);



	/*

	 * Put all the base refs.  Each css holds an extra reference to the
@@ -4354,9 +4380,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
	BUG_ON(!list_empty(&init_task.tasks));



	ss->active = 1;



	if (ss->post_create)

		ss->post_create(dummytop);

	online_css(ss, dummytop);



	mutex_unlock(&cgroup_mutex);
@@ -4469,9 +4493,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) 
	write_unlock(&css_set_lock);



	ss->active = 1;



	if (ss->post_create)

		ss->post_create(dummytop);

	online_css(ss, dummytop);



	/* success! */

	mutex_unlock(&cgroup_mutex);
@@ -4501,12 +4523,9 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) 
	 */

	BUG_ON(ss->root != &rootnode);



	/* ->pre_destroy() should be called outside cgroup_mutex for now */

	if (ss->pre_destroy)

		ss->pre_destroy(dummytop);



	mutex_lock(&cgroup_mutex);



	offline_css(ss, dummytop);

	ss->active = 0;



	if (ss->use_id) {

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