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cgroup: kill css_id
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The only user of css_id was memcg, and it has been convered to use
cgroup->id, so kill css_id.

Signed-off-by: Li Zefan <lizefan@huwei.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
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Li Zefan authored and Tejun Heo committed Sep 24, 2013
1 parent b862783 commit 2ff2a7d
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Showing 2 changed files with 1 addition and 284 deletions.
37 changes: 0 additions & 37 deletions include/linux/cgroup.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -612,11 +612,6 @@ struct cgroup_subsys {
int subsys_id;
int disabled;
int early_init;
/*
* True if this subsys uses ID. ID is not available before cgroup_init()
* (not available in early_init time.)
*/
bool use_id;

/*
* If %false, this subsystem is properly hierarchical -
Expand All @@ -642,9 +637,6 @@ struct cgroup_subsys {
*/
struct cgroupfs_root *root;
struct list_head sibling;
/* used when use_id == true */
struct idr idr;
spinlock_t id_lock;

/* list of cftype_sets */
struct list_head cftsets;
Expand Down Expand Up @@ -875,35 +867,6 @@ int css_scan_tasks(struct cgroup_subsys_state *css,
int cgroup_attach_task_all(struct task_struct *from, struct task_struct *);
int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from);

/*
* CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
* if cgroup_subsys.use_id == true. It can be used for looking up and scanning.
* CSS ID is assigned at cgroup allocation (create) automatically
* and removed when subsys calls free_css_id() function. This is because
* the lifetime of cgroup_subsys_state is subsys's matter.
*
* Looking up and scanning function should be called under rcu_read_lock().
* Taking cgroup_mutex is not necessary for following calls.
* But the css returned by this routine can be "not populated yet" or "being
* destroyed". The caller should check css and cgroup's status.
*/

/*
* Typically Called at ->destroy(), or somewhere the subsys frees
* cgroup_subsys_state.
*/
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);

/* Find a cgroup_subsys_state which has given ID */

struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id);

/* Returns true if root is ancestor of cg */
bool css_is_ancestor(struct cgroup_subsys_state *cg,
const struct cgroup_subsys_state *root);

/* Get id and depth of css */
unsigned short css_id(struct cgroup_subsys_state *css);
struct cgroup_subsys_state *css_from_dir(struct dentry *dentry,
struct cgroup_subsys *ss);

Expand Down
248 changes: 1 addition & 247 deletions kernel/cgroup.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -124,38 +124,6 @@ struct cfent {
struct simple_xattrs xattrs;
};

/*
* CSS ID -- ID per subsys's Cgroup Subsys State(CSS). used only when
* cgroup_subsys->use_id != 0.
*/
#define CSS_ID_MAX (65535)
struct css_id {
/*
* The css to which this ID points. This pointer is set to valid value
* after cgroup is populated. If cgroup is removed, this will be NULL.
* This pointer is expected to be RCU-safe because destroy()
* is called after synchronize_rcu(). But for safe use, css_tryget()
* should be used for avoiding race.
*/
struct cgroup_subsys_state __rcu *css;
/*
* ID of this css.
*/
unsigned short id;
/*
* Depth in hierarchy which this ID belongs to.
*/
unsigned short depth;
/*
* ID is freed by RCU. (and lookup routine is RCU safe.)
*/
struct rcu_head rcu_head;
/*
* Hierarchy of CSS ID belongs to.
*/
unsigned short stack[0]; /* Array of Length (depth+1) */
};

/*
* cgroup_event represents events which userspace want to receive.
*/
Expand Down Expand Up @@ -387,9 +355,6 @@ struct cgrp_cset_link {
static struct css_set init_css_set;
static struct cgrp_cset_link init_cgrp_cset_link;

static int cgroup_init_idr(struct cgroup_subsys *ss,
struct cgroup_subsys_state *css);

/*
* css_set_lock protects the list of css_set objects, and the chain of
* tasks off each css_set. Nests outside task->alloc_lock due to
Expand Down Expand Up @@ -841,8 +806,6 @@ static struct backing_dev_info cgroup_backing_dev_info = {
.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
};

static int alloc_css_id(struct cgroup_subsys_state *child_css);

static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
{
struct inode *inode = new_inode(sb);
Expand Down Expand Up @@ -4242,21 +4205,6 @@ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask)
goto err;
}
}

/* This cgroup is ready now */
for_each_root_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);
struct css_id *id = rcu_dereference_protected(css->id, true);

/*
* Update id->css pointer and make this css visible from
* CSS ID functions. This pointer will be dereferened
* from RCU-read-side without locks.
*/
if (id)
rcu_assign_pointer(id->css, css);
}

return 0;
err:
cgroup_clear_dir(cgrp, subsys_mask);
Expand Down Expand Up @@ -4325,7 +4273,6 @@ static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss,
css->cgroup = cgrp;
css->ss = ss;
css->flags = 0;
css->id = NULL;

if (cgrp->parent)
css->parent = cgroup_css(cgrp->parent, ss);
Expand Down Expand Up @@ -4457,12 +4404,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
goto err_free_all;

init_css(css, ss, cgrp);

if (ss->use_id) {
err = alloc_css_id(css);
if (err)
goto err_free_all;
}
}

/*
Expand Down Expand Up @@ -4927,12 +4868,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)

/* our new subsystem will be attached to the dummy hierarchy. */
init_css(css, ss, cgroup_dummy_top);
/* init_idr must be after init_css() because it sets css->id. */
if (ss->use_id) {
ret = cgroup_init_idr(ss, css);
if (ret)
goto err_unload;
}

/*
* Now we need to entangle the css into the existing css_sets. unlike
Expand Down Expand Up @@ -4998,9 +4933,6 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)

offline_css(cgroup_css(cgroup_dummy_top, ss));

if (ss->use_id)
idr_destroy(&ss->idr);

/* deassign the subsys_id */
cgroup_subsys[ss->subsys_id] = NULL;

Expand All @@ -5027,8 +4959,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)
/*
* remove subsystem's css from the cgroup_dummy_top and free it -
* need to free before marking as null because ss->css_free needs
* the cgrp->subsys pointer to find their state. note that this
* also takes care of freeing the css_id.
* the cgrp->subsys pointer to find their state.
*/
ss->css_free(cgroup_css(cgroup_dummy_top, ss));
RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL);
Expand Down Expand Up @@ -5099,8 +5030,6 @@ int __init cgroup_init(void)
for_each_builtin_subsys(ss, i) {
if (!ss->early_init)
cgroup_init_subsys(ss);
if (ss->use_id)
cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
}

/* allocate id for the dummy hierarchy */
Expand Down Expand Up @@ -5520,181 +5449,6 @@ static int __init cgroup_disable(char *str)
}
__setup("cgroup_disable=", cgroup_disable);

/*
* Functons for CSS ID.
*/

/* to get ID other than 0, this should be called when !cgroup_is_dead() */
unsigned short css_id(struct cgroup_subsys_state *css)
{
struct css_id *cssid;

/*
* This css_id() can return correct value when somone has refcnt
* on this or this is under rcu_read_lock(). Once css->id is allocated,
* it's unchanged until freed.
*/
cssid = rcu_dereference_raw(css->id);

if (cssid)
return cssid->id;
return 0;
}
EXPORT_SYMBOL_GPL(css_id);

/**
* css_is_ancestor - test "root" css is an ancestor of "child"
* @child: the css to be tested.
* @root: the css supporsed to be an ancestor of the child.
*
* Returns true if "root" is an ancestor of "child" in its hierarchy. Because
* this function reads css->id, the caller must hold rcu_read_lock().
* But, considering usual usage, the csses should be valid objects after test.
* Assuming that the caller will do some action to the child if this returns
* returns true, the caller must take "child";s reference count.
* If "child" is valid object and this returns true, "root" is valid, too.
*/

bool css_is_ancestor(struct cgroup_subsys_state *child,
const struct cgroup_subsys_state *root)
{
struct css_id *child_id;
struct css_id *root_id;

child_id = rcu_dereference(child->id);
if (!child_id)
return false;
root_id = rcu_dereference(root->id);
if (!root_id)
return false;
if (child_id->depth < root_id->depth)
return false;
if (child_id->stack[root_id->depth] != root_id->id)
return false;
return true;
}

void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css)
{
struct css_id *id = rcu_dereference_protected(css->id, true);

/* When this is called before css_id initialization, id can be NULL */
if (!id)
return;

BUG_ON(!ss->use_id);

rcu_assign_pointer(id->css, NULL);
rcu_assign_pointer(css->id, NULL);
spin_lock(&ss->id_lock);
idr_remove(&ss->idr, id->id);
spin_unlock(&ss->id_lock);
kfree_rcu(id, rcu_head);
}
EXPORT_SYMBOL_GPL(free_css_id);

/*
* This is called by init or create(). Then, calls to this function are
* always serialized (By cgroup_mutex() at create()).
*/

static struct css_id *get_new_cssid(struct cgroup_subsys *ss, int depth)
{
struct css_id *newid;
int ret, size;

BUG_ON(!ss->use_id);

size = sizeof(*newid) + sizeof(unsigned short) * (depth + 1);
newid = kzalloc(size, GFP_KERNEL);
if (!newid)
return ERR_PTR(-ENOMEM);

idr_preload(GFP_KERNEL);
spin_lock(&ss->id_lock);
/* Don't use 0. allocates an ID of 1-65535 */
ret = idr_alloc(&ss->idr, newid, 1, CSS_ID_MAX + 1, GFP_NOWAIT);
spin_unlock(&ss->id_lock);
idr_preload_end();

/* Returns error when there are no free spaces for new ID.*/
if (ret < 0)
goto err_out;

newid->id = ret;
newid->depth = depth;
return newid;
err_out:
kfree(newid);
return ERR_PTR(ret);

}

static int __init_or_module cgroup_init_idr(struct cgroup_subsys *ss,
struct cgroup_subsys_state *rootcss)
{
struct css_id *newid;

spin_lock_init(&ss->id_lock);
idr_init(&ss->idr);

newid = get_new_cssid(ss, 0);
if (IS_ERR(newid))
return PTR_ERR(newid);

newid->stack[0] = newid->id;
RCU_INIT_POINTER(newid->css, rootcss);
RCU_INIT_POINTER(rootcss->id, newid);
return 0;
}

static int alloc_css_id(struct cgroup_subsys_state *child_css)
{
struct cgroup_subsys_state *parent_css = css_parent(child_css);
struct css_id *child_id, *parent_id;
int i, depth;

parent_id = rcu_dereference_protected(parent_css->id, true);
depth = parent_id->depth + 1;

child_id = get_new_cssid(child_css->ss, depth);
if (IS_ERR(child_id))
return PTR_ERR(child_id);

for (i = 0; i < depth; i++)
child_id->stack[i] = parent_id->stack[i];
child_id->stack[depth] = child_id->id;
/*
* child_id->css pointer will be set after this cgroup is available
* see cgroup_populate_dir()
*/
rcu_assign_pointer(child_css->id, child_id);

return 0;
}

/**
* css_lookup - lookup css by id
* @ss: cgroup subsys to be looked into.
* @id: the id
*
* Returns pointer to cgroup_subsys_state if there is valid one with id.
* NULL if not. Should be called under rcu_read_lock()
*/
struct cgroup_subsys_state *css_lookup(struct cgroup_subsys *ss, int id)
{
struct css_id *cssid = NULL;

BUG_ON(!ss->use_id);
cssid = idr_find(&ss->idr, id);

if (unlikely(!cssid))
return NULL;

return rcu_dereference(cssid->css);
}
EXPORT_SYMBOL_GPL(css_lookup);

/**
* css_from_dir - get corresponding css from the dentry of a cgroup dir
* @dentry: directory dentry of interest
Expand Down

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