Skip to content

Commit

Permalink
cgroup: make cgroup_css() take cgroup_subsys * instead and allow NULL…
Browse files Browse the repository at this point in the history 
… 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: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
  • Loading branch information
Tejun Heo committed Aug 26, 2013
1 parent 35cf083 commit ca8bdca
Showing 1 changed file with 43 additions and 47 deletions.
90 changes: 43 additions & 47 deletions kernel/cgroup.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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],
lockdep_is_held(&cgroup_mutex));
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 */
Expand Down Expand Up @@ -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 */
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand All @@ -2135,7 +2138,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
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;
Expand Down Expand Up @@ -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 = NULL;
} else {
css = &cgrp->dummy_css;
}
css = cgroup_css(cgrp, cft->ss);
if (cft->ss && !css_tryget(css))
css = NULL;
rcu_read_unlock();

if (!css)
Expand Down Expand Up @@ -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))
Expand Down Expand Up @@ -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);

Expand Down Expand Up @@ -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;

Expand Down Expand Up @@ -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);

/*
Expand Down Expand Up @@ -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 */
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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);
}

/**
Expand Down

0 comments on commit ca8bdca

Please sign in to comment.