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Commit 30159ec7 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: implement for_each_[builtin_]subsys() 



There are quite a few places where all loaded [builtin] subsys are
iterated.  Implement for_each_[builtin_]subsys() and replace manual
iterations with those to simplify those places a bit.  The new
iterators automatically skip NULL subsystems.  This shouldn't cause
any functional difference.

Iteration loops which scan all subsystems and then skipping modular
ones explicitly are converted to use for_each_builtin_subsys().

While at it, reorder variable declarations and adjust whitespaces a
bit in the affected functions.

v2: Add lockdep_assert_held() in for_each_subsys() and add comments
    about synchronization as suggested by Li.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 82fe9b0d

kernel/cgroup.c

+71 −76
Original line number Diff line number Diff line
@@ -259,6 +259,31 @@ static int notify_on_release(const struct cgroup *cgrp) 
	return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);

}



/**

 * for_each_subsys - iterate all loaded cgroup subsystems

 * @ss: the iteration cursor

 * @i: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end

 *

 * Should be called under cgroup_mutex.

 */

#define for_each_subsys(ss, i)						\

	for ((i) = 0; (i) < CGROUP_SUBSYS_COUNT; (i)++)			\

		if (({ lockdep_assert_held(&cgroup_mutex);		\

		       !((ss) = cgroup_subsys[i]); })) { }		\

		else



/**

 * for_each_builtin_subsys - iterate all built-in cgroup subsystems

 * @ss: the iteration cursor

 * @i: the index of @ss, CGROUP_BUILTIN_SUBSYS_COUNT after reaching the end

 *

 * Bulit-in subsystems are always present and iteration itself doesn't

 * require any synchronization.

 */

#define for_each_builtin_subsys(ss, i)					\

	for ((i) = 0; (i) < CGROUP_BUILTIN_SUBSYS_COUNT &&		\

	     (((ss) = cgroup_subsys[i]) || true); (i)++)



/* iterate each subsystem attached to a hierarchy */

#define for_each_root_subsys(root, ss)					\

	list_for_each_entry((ss), &(root)->subsys_list, sibling)
@@ -356,10 +381,11 @@ static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS); 


static unsigned long css_set_hash(struct cgroup_subsys_state *css[])

{

	int i;

	unsigned long key = 0UL;

	struct cgroup_subsys *ss;

	int i;



	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++)

	for_each_subsys(ss, i)

		key += (unsigned long)css[i];

	key = (key >> 16) ^ key;
@@ -514,6 +540,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset, 
					struct cgroup_subsys_state *template[])

{

	struct cgroupfs_root *root = cgrp->root;

	struct cgroup_subsys *ss;

	struct css_set *cset;

	unsigned long key;

	int i;
@@ -523,7 +550,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset, 
	 * new css_set. while subsystems can change globally, the entries here

	 * won't change, so no need for locking.

	 */

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

	for_each_subsys(ss, i) {

		if (root->subsys_mask & (1UL << i)) {

			/* Subsystem is in this hierarchy. So we want

			 * the subsystem state from the new
@@ -982,23 +1009,19 @@ static int rebind_subsystems(struct cgroupfs_root *root, 
			     unsigned long added_mask, unsigned removed_mask)

{

	struct cgroup *cgrp = &root->top_cgroup;

	struct cgroup_subsys *ss;

	int i;



	BUG_ON(!mutex_is_locked(&cgroup_mutex));

	BUG_ON(!mutex_is_locked(&cgroup_root_mutex));



	/* Check that any added subsystems are currently free */

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

	for_each_subsys(ss, i) {

		unsigned long bit = 1UL << i;

		struct cgroup_subsys *ss = cgroup_subsys[i];



		if (!(bit & added_mask))

			continue;

		/*

		 * Nobody should tell us to do a subsys that doesn't exist:

		 * parse_cgroupfs_options should catch that case and refcounts

		 * ensure that subsystems won't disappear once selected.

		 */

		BUG_ON(ss == NULL);



		if (ss->root != &cgroup_dummy_root) {

			/* Subsystem isn't free */

			return -EBUSY;
@@ -1013,12 +1036,11 @@ static int rebind_subsystems(struct cgroupfs_root *root, 
		return -EBUSY;



	/* Process each subsystem */

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		struct cgroup_subsys *ss = cgroup_subsys[i];

	for_each_subsys(ss, i) {

		unsigned long bit = 1UL << i;



		if (bit & added_mask) {

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

			BUG_ON(ss == NULL);

			BUG_ON(cgrp->subsys[i]);

			BUG_ON(!cgroup_dummy_top->subsys[i]);

			BUG_ON(cgroup_dummy_top->subsys[i]->cgroup != cgroup_dummy_top);
@@ -1034,7 +1056,6 @@ static int rebind_subsystems(struct cgroupfs_root *root, 
			root->subsys_mask |= bit;

		} else if (bit & removed_mask) {

			/* We're removing this subsystem */

			BUG_ON(ss == NULL);

			BUG_ON(cgrp->subsys[i] != cgroup_dummy_top->subsys[i]);

			BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
@@ -1050,7 +1071,6 @@ static int rebind_subsystems(struct cgroupfs_root *root, 
			root->subsys_mask &= ~bit;

		} else if (bit & root->subsys_mask) {

			/* Subsystem state should already exist */

			BUG_ON(ss == NULL);

			BUG_ON(!cgrp->subsys[i]);

			/*

			 * a refcount was taken, but we already had one, so
@@ -1117,8 +1137,9 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
	char *token, *o = data;

	bool all_ss = false, one_ss = false;

	unsigned long mask = (unsigned long)-1;

	int i;

	bool module_pin_failed = false;

	struct cgroup_subsys *ss;

	int i;



	BUG_ON(!mutex_is_locked(&cgroup_mutex));
@@ -1195,10 +1216,7 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
			continue;

		}



		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

			struct cgroup_subsys *ss = cgroup_subsys[i];

			if (ss == NULL)

				continue;

		for_each_subsys(ss, i) {

			if (strcmp(token, ss->name))

				continue;

			if (ss->disabled)
@@ -1221,16 +1239,10 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
	 * otherwise if 'none', 'name=' and a subsystem name options

	 * were not specified, let's default to 'all'

	 */

	if (all_ss || (!one_ss && !opts->none && !opts->name)) {

		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

			struct cgroup_subsys *ss = cgroup_subsys[i];

			if (ss == NULL)

				continue;

			if (ss->disabled)

				continue;

	if (all_ss || (!one_ss && !opts->none && !opts->name))

		for_each_subsys(ss, i)

			if (!ss->disabled)

				set_bit(i, &opts->subsys_mask);

		}

	}



	/* Consistency checks */
@@ -1274,10 +1286,8 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 
	 * take duplicate reference counts on a subsystem that's already used,

	 * but rebind_subsystems handles this case.

	 */

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		unsigned long bit = 1UL << i;



		if (!(bit & opts->subsys_mask))

	for_each_subsys(ss, i) {

		if (!(opts->subsys_mask & (1UL << i)))

			continue;

		if (!try_module_get(cgroup_subsys[i]->module)) {

			module_pin_failed = true;
@@ -1306,11 +1316,11 @@ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) 


static void drop_parsed_module_refcounts(unsigned long subsys_mask)

{

	struct cgroup_subsys *ss;

	int i;

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		unsigned long bit = 1UL << i;



		if (!(bit & subsys_mask))

	for_each_subsys(ss, i) {

		if (!(subsys_mask & (1UL << i)))

			continue;

		module_put(cgroup_subsys[i]->module);

	}
@@ -4822,7 +4832,9 @@ EXPORT_SYMBOL_GPL(cgroup_unload_subsys); 
 */

int __init cgroup_init_early(void)

{

	struct cgroup_subsys *ss;

	int i;



	atomic_set(&init_css_set.refcount, 1);

	INIT_LIST_HEAD(&init_css_set.cgrp_links);

	INIT_LIST_HEAD(&init_css_set.tasks);
@@ -4837,13 +4849,8 @@ int __init cgroup_init_early(void) 
	list_add(&init_cgrp_cset_link.cset_link, &cgroup_dummy_top->cset_links);

	list_add(&init_cgrp_cset_link.cgrp_link, &init_css_set.cgrp_links);



	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		struct cgroup_subsys *ss = cgroup_subsys[i];



	/* at bootup time, we don't worry about modular subsystems */

		if (!ss || ss->module)

			continue;



	for_each_builtin_subsys(ss, i) {

		BUG_ON(!ss->name);

		BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);

		BUG_ON(!ss->css_alloc);
@@ -4868,20 +4875,15 @@ int __init cgroup_init_early(void) 
 */

int __init cgroup_init(void)

{

	int err;

	int i;

	struct cgroup_subsys *ss;

	unsigned long key;

	int i, err;



	err = bdi_init(&cgroup_backing_dev_info);

	if (err)

		return err;



	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		struct cgroup_subsys *ss = cgroup_subsys[i];



		/* at bootup time, we don't worry about modular subsystems */

		if (!ss || ss->module)

			continue;

	for_each_builtin_subsys(ss, i) {

		if (!ss->early_init)

			cgroup_init_subsys(ss);

		if (ss->use_id)
@@ -4990,6 +4992,7 @@ out: 
/* Display information about each subsystem and each hierarchy */

static int proc_cgroupstats_show(struct seq_file *m, void *v)

{

	struct cgroup_subsys *ss;

	int i;



	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
@@ -4999,14 +5002,12 @@ static int proc_cgroupstats_show(struct seq_file *m, void *v) 
	 * subsys/hierarchy state.

	 */

	mutex_lock(&cgroup_mutex);

	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

		struct cgroup_subsys *ss = cgroup_subsys[i];

		if (ss == NULL)

			continue;



	for_each_subsys(ss, i)

		seq_printf(m, "%s\t%d\t%d\t%d\n",

			   ss->name, ss->root->hierarchy_id,

			   ss->root->number_of_cgroups, !ss->disabled);

	}



	mutex_unlock(&cgroup_mutex);

	return 0;

}
@@ -5060,6 +5061,7 @@ void cgroup_fork(struct task_struct *child) 
 */

void cgroup_post_fork(struct task_struct *child)

{

	struct cgroup_subsys *ss;

	int i;



	/*
@@ -5096,14 +5098,11 @@ void cgroup_post_fork(struct task_struct *child) 
		 * of the array can be freed at module unload, so we

		 * can't touch that.

		 */

		for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {

			struct cgroup_subsys *ss = cgroup_subsys[i];



		for_each_builtin_subsys(ss, i)

			if (ss->fork)

				ss->fork(child);

	}

}

}



/**

 * cgroup_exit - detach cgroup from exiting task
@@ -5142,6 +5141,7 @@ void cgroup_post_fork(struct task_struct *child) 
 */

void cgroup_exit(struct task_struct *tsk, int run_callbacks)

{

	struct cgroup_subsys *ss;

	struct css_set *cset;

	int i;
@@ -5167,13 +5167,12 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks) 
		 * fork/exit callbacks are supported only for builtin

		 * subsystems, see cgroup_post_fork() for details.

		 */

		for (i = 0; i < CGROUP_BUILTIN_SUBSYS_COUNT; i++) {

			struct cgroup_subsys *ss = cgroup_subsys[i];



		for_each_builtin_subsys(ss, i) {

			if (ss->exit) {

				struct cgroup *old_cgrp =

					rcu_dereference_raw(cset->subsys[i])->cgroup;

				struct cgroup *cgrp = task_cgroup(tsk, i);



				ss->exit(cgrp, old_cgrp, tsk);

			}

		}
@@ -5280,23 +5279,19 @@ static void cgroup_release_agent(struct work_struct *work) 


static int __init cgroup_disable(char *str)

{

	int i;

	struct cgroup_subsys *ss;

	char *token;

	int i;



	while ((token = strsep(&str, ",")) != NULL) {

		if (!*token)

			continue;

		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {

			struct cgroup_subsys *ss = cgroup_subsys[i];



		/*

			 * cgroup_disable, being at boot time, can't

			 * know about module subsystems, so we don't

			 * worry about them.

		 * cgroup_disable, being at boot time, can't know about

		 * module subsystems, so we don't worry about them.

		 */

			if (!ss || ss->module)

				continue;



		for_each_builtin_subsys(ss, i) {

			if (!strcmp(token, ss->name)) {

				ss->disabled = 1;

				printk(KERN_INFO "Disabling %s control group"