Commit ca8bdcaf authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: make cgroup_css() take cgroup_subsys * instead and allow NULL subsys 



cgroup_css() is no longer used in hot paths.  Make it take struct
cgroup_subsys * and allow the users to specify NULL subsys to obtain
the dummy_css.  This removes open-coded NULL subsystem testing in a
couple users and generally simplifies the code.

After this patch, css_from_dir() also allows NULL @ss and returns the
matching dummy_css.  This behavior change doesn't affect its only user
- perf.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
Acked-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
parent 35cf0836

kernel/cgroup.c

+43 −47
Original line number Diff line number Diff line
@@ -226,19 +226,22 @@ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], 
/**

 * cgroup_css - obtain a cgroup's css for the specified subsystem

 * @cgrp: the cgroup of interest

 * @subsys_id: the subsystem of interest

 * @ss: the subsystem of interest (%NULL returns the dummy_css)

 *

 * Return @cgrp's css (cgroup_subsys_state) associated with @subsys_id.

 * This function must be called either under cgroup_mutex or

 * rcu_read_lock() and the caller is responsible for pinning the returned

 * css if it wants to keep accessing it outside the said locks.  This

 * function may return %NULL if @cgrp doesn't have @subsys_id enabled.

 * Return @cgrp's css (cgroup_subsys_state) associated with @ss.  This

 * function must be called either under cgroup_mutex or rcu_read_lock() and

 * the caller is responsible for pinning the returned css if it wants to

 * keep accessing it outside the said locks.  This function may return

 * %NULL if @cgrp doesn't have @subsys_id enabled.

 */

static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,

					      int subsys_id)

					      struct cgroup_subsys *ss)

{

	return rcu_dereference_check(cgrp->subsys[subsys_id],

	if (ss)

		return rcu_dereference_check(cgrp->subsys[ss->subsys_id],

					     lockdep_is_held(&cgroup_mutex));

	else

		return &cgrp->dummy_css;

}



/* convenient tests for these bits */
@@ -580,7 +583,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset, 
			/* Subsystem is in this hierarchy. So we want

			 * the subsystem state from the new

			 * cgroup */

			template[i] = cgroup_css(cgrp, i);

			template[i] = cgroup_css(cgrp, ss);

		} else {

			/* Subsystem is not in this hierarchy, so we

			 * don't want to change the subsystem state */
@@ -1062,30 +1065,30 @@ static int rebind_subsystems(struct cgroupfs_root *root, 


		if (bit & added_mask) {

			/* We're binding this subsystem to this hierarchy */

			BUG_ON(cgroup_css(cgrp, i));

			BUG_ON(!cgroup_css(cgroup_dummy_top, i));

			BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top);

			BUG_ON(cgroup_css(cgrp, ss));

			BUG_ON(!cgroup_css(cgroup_dummy_top, ss));

			BUG_ON(cgroup_css(cgroup_dummy_top, ss)->cgroup != cgroup_dummy_top);



			rcu_assign_pointer(cgrp->subsys[i],

					   cgroup_css(cgroup_dummy_top, i));

			cgroup_css(cgrp, i)->cgroup = cgrp;

					   cgroup_css(cgroup_dummy_top, ss));

			cgroup_css(cgrp, ss)->cgroup = cgrp;



			list_move(&ss->sibling, &root->subsys_list);

			ss->root = root;

			if (ss->bind)

				ss->bind(cgroup_css(cgrp, i));

				ss->bind(cgroup_css(cgrp, ss));



			/* refcount was already taken, and we're keeping it */

			root->subsys_mask |= bit;

		} else if (bit & removed_mask) {

			/* We're removing this subsystem */

			BUG_ON(cgroup_css(cgrp, i) != cgroup_css(cgroup_dummy_top, i));

			BUG_ON(cgroup_css(cgrp, i)->cgroup != cgrp);

			BUG_ON(cgroup_css(cgrp, ss) != cgroup_css(cgroup_dummy_top, ss));

			BUG_ON(cgroup_css(cgrp, ss)->cgroup != cgrp);



			if (ss->bind)

				ss->bind(cgroup_css(cgroup_dummy_top, i));

				ss->bind(cgroup_css(cgroup_dummy_top, ss));



			cgroup_css(cgroup_dummy_top, i)->cgroup = cgroup_dummy_top;

			cgroup_css(cgroup_dummy_top, ss)->cgroup = cgroup_dummy_top;

			RCU_INIT_POINTER(cgrp->subsys[i], NULL);



			cgroup_subsys[i]->root = &cgroup_dummy_root;
@@ -1930,7 +1933,7 @@ EXPORT_SYMBOL_GPL(cgroup_taskset_next); 
struct cgroup_subsys_state *cgroup_taskset_cur_css(struct cgroup_taskset *tset,

						   int subsys_id)

{

	return cgroup_css(tset->cur_cgrp, subsys_id);

	return cgroup_css(tset->cur_cgrp, cgroup_subsys[subsys_id]);

}

EXPORT_SYMBOL_GPL(cgroup_taskset_cur_css);
@@ -2071,7 +2074,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk, 
	 * step 1: check that we can legitimately attach to the cgroup.

	 */

	for_each_root_subsys(root, ss) {

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);



		if (ss->can_attach) {

			retval = ss->can_attach(css, &tset);
@@ -2113,7 +2116,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk, 
	 * step 4: do subsystem attach callbacks.

	 */

	for_each_root_subsys(root, ss) {

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);



		if (ss->attach)

			ss->attach(css, &tset);
@@ -2135,7 +2138,7 @@ out_put_css_set_refs: 
out_cancel_attach:

	if (retval) {

		for_each_root_subsys(root, ss) {

			struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);

			struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);



			if (ss == failed_ss)

				break;
@@ -2481,13 +2484,9 @@ static int cgroup_file_open(struct inode *inode, struct file *file) 
	 * @css stays alive for all file operations.

	 */

	rcu_read_lock();

	if (cft->ss) {

		css = cgroup_css(cgrp, cft->ss->subsys_id);

		if (!css_tryget(css))

	css = cgroup_css(cgrp, cft->ss);

	if (cft->ss && !css_tryget(css))

		css = NULL;

	} else {

		css = &cgrp->dummy_css;

	}

	rcu_read_unlock();



	if (!css)
@@ -2878,7 +2877,7 @@ static int cgroup_cfts_commit(struct cftype *cfts, bool is_add) 


	/* add/rm files for all cgroups created before */

	rcu_read_lock();

	css_for_each_descendant_pre(css, cgroup_css(root, ss->subsys_id)) {

	css_for_each_descendant_pre(css, cgroup_css(root, ss)) {

		struct cgroup *cgrp = css->cgroup;



		if (cgroup_is_dead(cgrp))
@@ -3082,10 +3081,7 @@ css_next_child(struct cgroup_subsys_state *pos_css, 
	if (&next->sibling == &cgrp->children)

		return NULL;



	if (parent_css->ss)

		return cgroup_css(next, parent_css->ss->subsys_id);

	else

		return &next->dummy_css;

	return cgroup_css(next, parent_css->ss);

}

EXPORT_SYMBOL_GPL(css_next_child);
@@ -4110,7 +4106,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css, 
	rcu_read_lock();



	ret = -EINVAL;

	event->css = cgroup_css(cgrp, event->cft->ss->subsys_id);

	event->css = cgroup_css(cgrp, event->cft->ss);

	if (event->css)

		ret = 0;
@@ -4266,7 +4262,7 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask) 


	/* This cgroup is ready now */

	for_each_root_subsys(cgrp->root, ss) {

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);

		struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);

		struct css_id *id = rcu_dereference_protected(css->id, true);



		/*
@@ -4349,11 +4345,11 @@ static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss, 
	css->id = NULL;



	if (cgrp->parent)

		css->parent = cgroup_css(cgrp->parent, ss->subsys_id);

		css->parent = cgroup_css(cgrp->parent, ss);

	else

		css->flags |= CSS_ROOT;



	BUG_ON(cgroup_css(cgrp, ss->subsys_id));

	BUG_ON(cgroup_css(cgrp, ss));

}



/* invoke ->css_online() on a new CSS and mark it online if successful */
@@ -4466,7 +4462,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, 
	for_each_root_subsys(root, ss) {

		struct cgroup_subsys_state *css;



		css = ss->css_alloc(cgroup_css(parent, ss->subsys_id));

		css = ss->css_alloc(cgroup_css(parent, ss));

		if (IS_ERR(css)) {

			err = PTR_ERR(css);

			goto err_free_all;
@@ -4712,7 +4708,7 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) 
	 * percpu refs of all css's are confirmed to be killed.

	 */

	for_each_root_subsys(cgrp->root, ss)

		kill_css(cgroup_css(cgrp, ss->subsys_id));

		kill_css(cgroup_css(cgrp, ss));



	/*

	 * Mark @cgrp dead.  This prevents further task migration and child
@@ -4839,7 +4835,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) 
	/* Create the top cgroup state for this subsystem */

	list_add(&ss->sibling, &cgroup_dummy_root.subsys_list);

	ss->root = &cgroup_dummy_root;

	css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss->subsys_id));

	css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss));

	/* We don't handle early failures gracefully */

	BUG_ON(IS_ERR(css));

	init_css(css, ss, cgroup_dummy_top);
@@ -4918,7 +4914,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) 
	 * struct, so this can happen first (i.e. before the dummy root

	 * attachment).

	 */

	css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss->subsys_id));

	css = ss->css_alloc(cgroup_css(cgroup_dummy_top, ss));

	if (IS_ERR(css)) {

		/* failure case - need to deassign the cgroup_subsys[] slot. */

		cgroup_subsys[ss->subsys_id] = NULL;
@@ -5000,7 +4996,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) 


	mutex_lock(&cgroup_mutex);



	offline_css(cgroup_css(cgroup_dummy_top, ss->subsys_id));

	offline_css(cgroup_css(cgroup_dummy_top, ss));



	if (ss->use_id)

		idr_destroy(&ss->idr);
@@ -5034,7 +5030,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) 
	 * the cgrp->subsys pointer to find their state. note that this

	 * also takes care of freeing the css_id.

	 */

	ss->css_free(cgroup_css(cgroup_dummy_top, ss->subsys_id));

	ss->css_free(cgroup_css(cgroup_dummy_top, ss));

	RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL);



	mutex_unlock(&cgroup_mutex);
@@ -5721,7 +5717,7 @@ struct cgroup_subsys_state *css_from_dir(struct dentry *dentry, 
		return ERR_PTR(-EBADF);



	cgrp = __d_cgrp(dentry);

	return cgroup_css(cgrp, ss->subsys_id) ?: ERR_PTR(-ENOENT);

	return cgroup_css(cgrp, ss) ?: ERR_PTR(-ENOENT);

}



/**

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