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Subject[PATCH 1/5] cgroup: do ID allocation under css allocator.
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Now, css'id is allocated after ->create() is called. But to make use of ID
in ->create(), it should be available before ->create().

In another thinking, considering the ID is tightly coupled with "css",
it should be allocated when "css" is allocated.
This patch moves alloc_css_id() to css allocation routine. Now, only 2 subsys,
memory and blkio are useing ID. (To support complicated hierarchy walk.)

ID will be used in mem cgroup's ->create(), later.

Note:
If someone changes rules of css allocation, ID allocation should be moved too.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
block/blk-cgroup.c | 9 ++++++++
include/linux/cgroup.h | 16 ++++++++-------
kernel/cgroup.c | 50 ++++++++++++++-----------------------------------
mm/memcontrol.c | 5 ++++
4 files changed, 38 insertions(+), 42 deletions(-)
Index: mmotm-0811/kernel/cgroup.c
===================================================================
--- mmotm-0811.orig/kernel/cgroup.c
+++ mmotm-0811/kernel/cgroup.c
@@ -289,9 +289,6 @@ struct cg_cgroup_link {
static struct css_set init_css_set;
static struct cg_cgroup_link init_css_set_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() */
@@ -770,9 +767,6 @@ static struct backing_dev_info cgroup_ba
.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(mode_t mode, struct super_block *sb)
{
struct inode *inode = new_inode(sb);
@@ -3257,7 +3251,8 @@ static void init_cgroup_css(struct cgrou
css->cgroup = cgrp;
atomic_set(&css->refcnt, 1);
css->flags = 0;
- css->id = NULL;
+ if (!ss->use_id)
+ css->id = NULL;
if (cgrp == dummytop)
set_bit(CSS_ROOT, &css->flags);
BUG_ON(cgrp->subsys[ss->subsys_id]);
@@ -3342,12 +3337,6 @@ static long cgroup_create(struct cgroup
goto err_destroy;
}
init_cgroup_css(css, ss, cgrp);
- if (ss->use_id) {
- err = alloc_css_id(ss, parent, cgrp);
- if (err)
- goto err_destroy;
- }
- /* At error, ->destroy() callback has to free assigned ID. */
}

cgroup_lock_hierarchy(root);
@@ -3709,17 +3698,6 @@ int __init_or_module cgroup_load_subsys(

/* our new subsystem will be attached to the dummy hierarchy. */
init_cgroup_css(css, ss, dummytop);
- /* init_idr must be after init_cgroup_css because it sets css->id. */
- if (ss->use_id) {
- int ret = cgroup_init_idr(ss, css);
- if (ret) {
- dummytop->subsys[ss->subsys_id] = NULL;
- ss->destroy(ss, dummytop);
- subsys[i] = NULL;
- mutex_unlock(&cgroup_mutex);
- return ret;
- }
- }

/*
* Now we need to entangle the css into the existing css_sets. unlike
@@ -3888,8 +3866,6 @@ int __init cgroup_init(void)
struct cgroup_subsys *ss = subsys[i];
if (!ss->early_init)
cgroup_init_subsys(ss);
- if (ss->use_id)
- cgroup_init_idr(ss, init_css_set.subsys[ss->subsys_id]);
}

/* Add init_css_set to the hash table */
@@ -4603,8 +4579,8 @@ err_out:

}

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

@@ -4616,21 +4592,25 @@ static int __init_or_module cgroup_init_
return PTR_ERR(newid);

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

-static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
- struct cgroup *child)
+int alloc_css_id(struct cgroup_subsys *ss,
+ struct cgroup *cgrp, struct cgroup_subsys_state *css)
{
int subsys_id, i, depth = 0;
- struct cgroup_subsys_state *parent_css, *child_css;
+ struct cgroup_subsys_state *parent_css;
+ struct cgroup *parent;
struct css_id *child_id, *parent_id;

+ if (cgrp == dummytop)
+ return cgroup_init_idr(ss, css);
+
+ parent = cgrp->parent;
subsys_id = ss->subsys_id;
parent_css = parent->subsys[subsys_id];
- child_css = child->subsys[subsys_id];
parent_id = parent_css->id;
depth = parent_id->depth + 1;

@@ -4645,7 +4625,7 @@ static int alloc_css_id(struct cgroup_su
* child_id->css pointer will be set after this cgroup is available
* see cgroup_populate_dir()
*/
- rcu_assign_pointer(child_css->id, child_id);
+ rcu_assign_pointer(css->id, child_id);

return 0;
}
Index: mmotm-0811/include/linux/cgroup.h
===================================================================
--- mmotm-0811.orig/include/linux/cgroup.h
+++ mmotm-0811/include/linux/cgroup.h
@@ -583,9 +583,11 @@ int cgroup_attach_task_current_cg(struct
/*
* 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.
+ * CSS ID must be assigned by subsys itself at cgroup creation and deleted
+ * when subsys calls free_css_id() function. This is because the life time of
+ * of cgroup_subsys_state is subsys's matter.
+ *
+ * ID->css look up is available after cgroup's directory is populated.
*
* Looking up and scanning function should be called under rcu_read_lock().
* Taking cgroup_mutex()/hierarchy_mutex() is not necessary for following calls.
@@ -593,10 +595,10 @@ int cgroup_attach_task_current_cg(struct
* destroyed". The caller should check css and cgroup's status.
*/

-/*
- * Typically Called at ->destroy(), or somewhere the subsys frees
- * cgroup_subsys_state.
- */
+/* Should be called in ->create() by subsys itself */
+int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *newgr,
+ struct cgroup_subsys_state *css);
+/* Typically Called at ->destroy(), or somewhere the subsys frees css */
void free_css_id(struct cgroup_subsys *ss, struct cgroup_subsys_state *css);

/* Find a cgroup_subsys_state which has given ID */
Index: mmotm-0811/mm/memcontrol.c
===================================================================
--- mmotm-0811.orig/mm/memcontrol.c
+++ mmotm-0811/mm/memcontrol.c
@@ -4141,6 +4141,11 @@ mem_cgroup_create(struct cgroup_subsys *
if (alloc_mem_cgroup_per_zone_info(mem, node))
goto free_out;

+ error = alloc_css_id(ss, cont, &mem->css);
+ if (error)
+ goto free_out;
+ /* Here, css_id(&mem->css) works. but css_lookup(id)->mem doesn't */
+
/* root ? */
if (cont->parent == NULL) {
int cpu;
Index: mmotm-0811/block/blk-cgroup.c
===================================================================
--- mmotm-0811.orig/block/blk-cgroup.c
+++ mmotm-0811/block/blk-cgroup.c
@@ -958,9 +958,13 @@ blkiocg_create(struct cgroup_subsys *sub
{
struct blkio_cgroup *blkcg;
struct cgroup *parent = cgroup->parent;
+ int ret;

if (!parent) {
blkcg = &blkio_root_cgroup;
+ ret = alloc_css_id(subsys, cgroup, &blkcg->css);
+ if (ret)
+ return ERR_PTR(ret);
goto done;
}

@@ -971,6 +975,11 @@ blkiocg_create(struct cgroup_subsys *sub
blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL);
if (!blkcg)
return ERR_PTR(-ENOMEM);
+ ret = alloc_css_id(subsys, cgroup, &blkcg->css);
+ if (ret) {
+ kfree(blkcg);
+ return ERR_PTR(ret);
+ }

blkcg->weight = BLKIO_WEIGHT_DEFAULT;
done:


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