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    Subject[PATCH v4 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>
    Reviewed-by: Michal Hocko <mhocko@suse.cz>
    ---
    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 4ef8452..c07e175 100644
    --- a/include/linux/cgroup.h
    +++ b/include/linux/cgroup.h
    @@ -597,11 +597,6 @@ 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 -
    @@ -627,9 +622,6 @@ 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;
    @@ -874,35 +866,6 @@ 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 a26e083..a64b7b8 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;
    - }
    }

    /*
    @@ -4746,12 +4687,6 @@ 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
    @@ -4817,9 +4752,6 @@ 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;

    @@ -4846,8 +4778,7 @@ 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;
    @@ -4918,8 +4849,6 @@ 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 */
    @@ -5340,185 +5269,6 @@ 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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