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cgroup: implement for_each_[builtin_]subsys()
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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: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
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Tejun Heo committed Jun 25, 2013
1 parent 82fe9b0 commit 30159ec
Showing 1 changed file with 71 additions and 76 deletions.
147 changes: 71 additions & 76 deletions kernel/cgroup.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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;
Expand All @@ -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
Expand Down Expand Up @@ -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;
Expand All @@ -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);
Expand All @@ -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);

Expand All @@ -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
Expand Down Expand Up @@ -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));

Expand Down Expand Up @@ -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)
Expand All @@ -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;
set_bit(i, &opts->subsys_mask);
}
}
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 */

Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
}
Expand Down Expand Up @@ -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);
Expand All @@ -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;

/* at bootup time, we don't worry about modular subsystems */
for_each_builtin_subsys(ss, i) {
BUG_ON(!ss->name);
BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
BUG_ON(!ss->css_alloc);
Expand All @@ -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)
Expand Down Expand Up @@ -4990,6 +4992,7 @@ int proc_cgroup_show(struct seq_file *m, void *v)
/* 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");
Expand All @@ -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;
}
Expand Down Expand Up @@ -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;

/*
Expand Down Expand Up @@ -5096,12 +5098,9 @@ 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);
}
}
}

Expand Down Expand Up @@ -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;

Expand All @@ -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);
}
}
Expand Down Expand Up @@ -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.
*/
if (!ss || ss->module)
continue;

/*
* cgroup_disable, being at boot time, can't know about
* module subsystems, so we don't worry about them.
*/
for_each_builtin_subsys(ss, i) {
if (!strcmp(token, ss->name)) {
ss->disabled = 1;
printk(KERN_INFO "Disabling %s control group"
Expand Down

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