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Commit 2ff2a7d0 authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

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: default avatarLi Zefan <lizefan@huwei.com>
Reviewed-by: default avatarMichal Hocko <mhocko@suse.cz>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent b8627835
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+0 −37
Original line number Diff line number Diff line
@@ -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 -
@@ -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;
@@ -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);

+1 −247
Original line number Diff line number Diff line
@@ -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.
 */
@@ -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
@@ -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);
@@ -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);
@@ -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);
@@ -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;
		}
	}

	/*
@@ -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
@@ -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;

@@ -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);
@@ -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 */
@@ -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