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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: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
This commit is contained in:
Tejun Heo 2013-08-26 18:40:56 -04:00
Родитель 35cf083619
Коммит ca8bdcaff0
1 изменённых файлов: 43 добавлений и 47 удалений
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90
kernel/cgroup.c
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@ -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 * cgroup_css - obtain a cgroup's css for the specified subsystem
* @cgrp: the cgroup of interest * @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. * Return @cgrp's css (cgroup_subsys_state) associated with @ss. This
* This function must be called either under cgroup_mutex or * function must be called either under cgroup_mutex or rcu_read_lock() and
* rcu_read_lock() and the caller is responsible for pinning the returned * the caller is responsible for pinning the returned css if it wants to
* css if it wants to keep accessing it outside the said locks. This * keep accessing it outside the said locks. This function may return
* function may return %NULL if @cgrp doesn't have @subsys_id enabled. * %NULL if @cgrp doesn't have @subsys_id enabled.
*/ */
static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp, 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)
lockdep_is_held(&cgroup_mutex)); return rcu_dereference_check(cgrp->subsys[ss->subsys_id],
lockdep_is_held(&cgroup_mutex));
else
return &cgrp->dummy_css;
} }
/* convenient tests for these bits */ /* 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 /* Subsystem is in this hierarchy. So we want
* the subsystem state from the new * the subsystem state from the new
* cgroup */ * cgroup */
template[i] = cgroup_css(cgrp, i); template[i] = cgroup_css(cgrp, ss);
} else { } else {
/* Subsystem is not in this hierarchy, so we /* Subsystem is not in this hierarchy, so we
* don't want to change the subsystem state */ * don't want to change the subsystem state */
@ -1062,30 +1065,30 @@ static int rebind_subsystems(struct cgroupfs_root *root,
if (bit & added_mask) { if (bit & added_mask) {
/* We're binding this subsystem to this hierarchy */ /* We're binding this subsystem to this hierarchy */
BUG_ON(cgroup_css(cgrp, i)); BUG_ON(cgroup_css(cgrp, ss));
BUG_ON(!cgroup_css(cgroup_dummy_top, i)); BUG_ON(!cgroup_css(cgroup_dummy_top, ss));
BUG_ON(cgroup_css(cgroup_dummy_top, i)->cgroup != cgroup_dummy_top); BUG_ON(cgroup_css(cgroup_dummy_top, ss)->cgroup != cgroup_dummy_top);
rcu_assign_pointer(cgrp->subsys[i], rcu_assign_pointer(cgrp->subsys[i],
cgroup_css(cgroup_dummy_top, i)); cgroup_css(cgroup_dummy_top, ss));
cgroup_css(cgrp, i)->cgroup = cgrp; cgroup_css(cgrp, ss)->cgroup = cgrp;
list_move(&ss->sibling, &root->subsys_list); list_move(&ss->sibling, &root->subsys_list);
ss->root = root; ss->root = root;
if (ss->bind) if (ss->bind)
ss->bind(cgroup_css(cgrp, i)); ss->bind(cgroup_css(cgrp, ss));
/* refcount was already taken, and we're keeping it */ /* refcount was already taken, and we're keeping it */
root->subsys_mask |= bit; root->subsys_mask |= bit;
} else if (bit & removed_mask) { } else if (bit & removed_mask) {
/* We're removing this subsystem */ /* We're removing this subsystem */
BUG_ON(cgroup_css(cgrp, i) != cgroup_css(cgroup_dummy_top, i)); BUG_ON(cgroup_css(cgrp, ss) != cgroup_css(cgroup_dummy_top, ss));
BUG_ON(cgroup_css(cgrp, i)->cgroup != cgrp); BUG_ON(cgroup_css(cgrp, ss)->cgroup != cgrp);
if (ss->bind) 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); RCU_INIT_POINTER(cgrp->subsys[i], NULL);
cgroup_subsys[i]->root = &cgroup_dummy_root; 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, struct cgroup_subsys_state *cgroup_taskset_cur_css(struct cgroup_taskset *tset,
int subsys_id) 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); 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. * step 1: check that we can legitimately attach to the cgroup.
*/ */
for_each_root_subsys(root, ss) { 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) { if (ss->can_attach) {
retval = ss->can_attach(css, &tset); 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. * step 4: do subsystem attach callbacks.
*/ */
for_each_root_subsys(root, ss) { 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) if (ss->attach)
ss->attach(css, &tset); ss->attach(css, &tset);
@ -2135,7 +2138,7 @@ out_put_css_set_refs:
out_cancel_attach: out_cancel_attach:
if (retval) { if (retval) {
for_each_root_subsys(root, ss) { 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) if (ss == failed_ss)
break; break;
@ -2481,13 +2484,9 @@ static int cgroup_file_open(struct inode *inode, struct file *file)
* @css stays alive for all file operations. * @css stays alive for all file operations.
*/ */
rcu_read_lock(); rcu_read_lock();
if (cft->ss) { css = cgroup_css(cgrp, cft->ss);
css = cgroup_css(cgrp, cft->ss->subsys_id); if (cft->ss && !css_tryget(css))
if (!css_tryget(css)) css = NULL;
css = NULL;
} else {
css = &cgrp->dummy_css;
}
rcu_read_unlock(); rcu_read_unlock();
if (!css) 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 */ /* add/rm files for all cgroups created before */
rcu_read_lock(); 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; struct cgroup *cgrp = css->cgroup;
if (cgroup_is_dead(cgrp)) if (cgroup_is_dead(cgrp))
@ -3082,10 +3081,7 @@ css_next_child(struct cgroup_subsys_state *pos_css,
if (&next->sibling == &cgrp->children) if (&next->sibling == &cgrp->children)
return NULL; return NULL;
if (parent_css->ss) return cgroup_css(next, parent_css->ss);
return cgroup_css(next, parent_css->ss->subsys_id);
else
return &next->dummy_css;
} }
EXPORT_SYMBOL_GPL(css_next_child); 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(); rcu_read_lock();
ret = -EINVAL; ret = -EINVAL;
event->css = cgroup_css(cgrp, event->cft->ss->subsys_id); event->css = cgroup_css(cgrp, event->cft->ss);
if (event->css) if (event->css)
ret = 0; ret = 0;
@ -4266,7 +4262,7 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
/* This cgroup is ready now */ /* This cgroup is ready now */
for_each_root_subsys(cgrp->root, ss) { 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); 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; css->id = NULL;
if (cgrp->parent) if (cgrp->parent)
css->parent = cgroup_css(cgrp->parent, ss->subsys_id); css->parent = cgroup_css(cgrp->parent, ss);
else else
css->flags |= CSS_ROOT; 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 */ /* 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) { for_each_root_subsys(root, ss) {
struct cgroup_subsys_state *css; 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)) { if (IS_ERR(css)) {
err = PTR_ERR(css); err = PTR_ERR(css);
goto err_free_all; 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. * percpu refs of all css's are confirmed to be killed.
*/ */
for_each_root_subsys(cgrp->root, ss) 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 * 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 */ /* Create the top cgroup state for this subsystem */
list_add(&ss->sibling, &cgroup_dummy_root.subsys_list); list_add(&ss->sibling, &cgroup_dummy_root.subsys_list);
ss->root = &cgroup_dummy_root; 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 */ /* We don't handle early failures gracefully */
BUG_ON(IS_ERR(css)); BUG_ON(IS_ERR(css));
init_css(css, ss, cgroup_dummy_top); 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 * struct, so this can happen first (i.e. before the dummy root
* attachment). * 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)) { if (IS_ERR(css)) {
/* failure case - need to deassign the cgroup_subsys[] slot. */ /* failure case - need to deassign the cgroup_subsys[] slot. */
cgroup_subsys[ss->subsys_id] = NULL; cgroup_subsys[ss->subsys_id] = NULL;
@ -5000,7 +4996,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
mutex_lock(&cgroup_mutex); 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) if (ss->use_id)
idr_destroy(&ss->idr); 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 * the cgrp->subsys pointer to find their state. note that this
* also takes care of freeing the css_id. * 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); RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL);
mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_mutex);
@ -5721,7 +5717,7 @@ struct cgroup_subsys_state *css_from_dir(struct dentry *dentry,
return ERR_PTR(-EBADF); return ERR_PTR(-EBADF);
cgrp = __d_cgrp(dentry); cgrp = __d_cgrp(dentry);
return cgroup_css(cgrp, ss->subsys_id) ?: ERR_PTR(-ENOENT); return cgroup_css(cgrp, ss) ?: ERR_PTR(-ENOENT);
} }
/** /**