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Subject[PATCH v2 8/8] cgroup: kill css_id
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>
---
include/linux/cgroup.h | 37 --------
kernel/cgroup.c | 252 +------------------------------------------------
2 files changed, 1 insertion(+), 288 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e8eb361..ec8c380 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -599,11 +599,6 @@ 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 -
@@ -629,9 +624,6 @@ 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;
@@ -858,35 +850,6 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan);
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 *cgroup_css_from_dir(struct file *f, int id);

#else /* !CONFIG_CGROUPS */
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9b27775..4333cb7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -123,38 +123,6 @@ struct cfent {
};

/*
- * 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.
*/
struct cgroup_event {
@@ -364,9 +332,6 @@ 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 cgroup_iter_start() */
@@ -815,9 +780,6 @@ static struct backing_dev_info cgroup_backing_dev_info = {
.capabilities = BDI_CAP_NO_ACCT_AND_WRITEBACK,
};

-static int alloc_css_id(struct cgroup_subsys *ss,
- struct cgroup *parent, struct cgroup *child);
-
static struct inode *cgroup_new_inode(umode_t mode, struct super_block *sb)
{
struct inode *inode = new_inode(sb);
@@ -4160,20 +4122,6 @@ 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 = cgrp->subsys[ss->subsys_id];
- 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);
@@ -4202,7 +4150,6 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
{
css->cgroup = cgrp;
css->flags = 0;
- css->id = NULL;
if (cgrp == cgroup_dummy_top)
css->flags |= CSS_ROOT;
BUG_ON(cgrp->subsys[ss->subsys_id]);
@@ -4331,12 +4278,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
goto err_free_all;

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

/*
@@ -4741,12 +4682,6 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss)

/* our new subsystem will be attached to the dummy hierarchy. */
init_cgroup_css(css, ss, cgroup_dummy_top);
- /* init_idr must be after init_cgroup_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
@@ -4812,9 +4747,6 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss)

offline_css(ss, cgroup_dummy_top);

- if (ss->use_id)
- idr_destroy(&ss->idr);
-
/* deassign the subsys_id */
cgroup_subsys[ss->subsys_id] = NULL;

@@ -4841,8 +4773,7 @@ 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_dummy_top);
cgroup_dummy_top->subsys[ss->subsys_id] = NULL;
@@ -4913,8 +4844,6 @@ 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 */
@@ -5335,185 +5264,6 @@ 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 *ss, struct cgroup *parent,
- struct cgroup *child)
-{
- int subsys_id, i, depth = 0;
- struct cgroup_subsys_state *parent_css, *child_css;
- struct css_id *child_id, *parent_id;
-
- subsys_id = ss->subsys_id;
- parent_css = parent->subsys[subsys_id];
- child_css = child->subsys[subsys_id];
- parent_id = rcu_dereference_protected(parent_css->id, true);
- depth = parent_id->depth + 1;
-
- child_id = get_new_cssid(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);
-
-/*
* get corresponding css from file open on cgroupfs directory
*/
struct cgroup_subsys_state *cgroup_css_from_dir(struct file *f, int id)
--
1.8.0.2

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