cgroup, cpuset: remove cgroup_subsys->post_clone()

Currently CGRP_CPUSET_CLONE_CHILDREN triggers ->post_clone().  Now
that clone_children is cpuset specific, there's no reason to have this
rather odd option activation mechanism in cgroup core.  cpuset can
check the flag from its ->css_allocate() and take the necessary
action.

Move cpuset_post_clone() logic to the end of cpuset_css_alloc() and
remove cgroup_subsys->post_clone().

Loosely based on Glauber's "generalize post_clone into post_create"
patch.

Signed-off-by: Tejun Heo <tj@kernel.org>
Original-patch-by: Glauber Costa <glommer@parallels.com>
Original-patch: <1351686554-22592-2-git-send-email-glommer@parallels.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Glauber Costa <glommer@parallels.com>

4 files changed, 36 insertions, 57 deletions

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 24cdf76bd20c..bcf1a00b06a1 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -642,14 +642,6 @@ void exit(struct task_struct *task)
 
 Called during task exit.
 
-void post_clone(struct cgroup *cgrp)
-(cgroup_mutex held by caller)
-
-Called during cgroup_create() to do any parameter
-initialization which might be required before a task could attach.  For
-example, in cpusets, no task may attach before 'cpus' and 'mems' are set
-up.
-
 void bind(struct cgroup *root)
 (cgroup_mutex held by caller)
 
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index d2f82979f6c1..c798997e5011 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -452,7 +452,6 @@ struct cgroup_subsys {
         void (*fork)(struct task_struct *task);
         void (*exit)(struct cgroup *cgrp, struct cgroup *old_cgrp,
                      struct task_struct *task);
-        void (*post_clone)(struct cgroup *cgrp);
         void (*bind)(struct cgroup *root);
 
         int subsys_id;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 2895880e6800..96719f73e95d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4142,10 +4142,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
                         if (err)
                                 goto err_free_all;
                 }
-                /* At error, ->css_free() callback has to free assigned ID. */
-                if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags) &&
-                    ss->post_clone)
-                        ss->post_clone(cgrp);
 
                 if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
                     parent->parent) {
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 06931337c4e5..b017887d632f 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1784,56 +1784,20 @@ static struct cftype files[] = {
 };
 
 /*
- * post_clone() is called during cgroup_create() when the
- * clone_children mount argument was specified.  The cgroup
- * can not yet have any tasks.
- *
- * Currently we refuse to set up the cgroup - thereby
- * refusing the task to be entered, and as a result refusing
- * the sys_unshare() or clone() which initiated it - if any
- * sibling cpusets have exclusive cpus or mem.
- *
- * If this becomes a problem for some users who wish to
- * allow that scenario, then cpuset_post_clone() could be
- * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
- * (and likewise for mems) to the new cgroup. Called with cgroup_mutex
- * held.
- */
-static void cpuset_post_clone(struct cgroup *cgroup)
-{
-        struct cgroup *parent, *child;
-        struct cpuset *cs, *parent_cs;
-
-        parent = cgroup->parent;
-        list_for_each_entry(child, &parent->children, sibling) {
-                cs = cgroup_cs(child);
-                if (is_mem_exclusive(cs) || is_cpu_exclusive(cs))
-                        return;
-        }
-        cs = cgroup_cs(cgroup);
-        parent_cs = cgroup_cs(parent);
-
-        mutex_lock(&callback_mutex);
-        cs->mems_allowed = parent_cs->mems_allowed;
-        cpumask_copy(cs->cpus_allowed, parent_cs->cpus_allowed);
-        mutex_unlock(&callback_mutex);
-        return;
-}
-
-/*
  *      cpuset_css_alloc - allocate a cpuset css
  *      cont:   control group that the new cpuset will be part of
  */
 
 static struct cgroup_subsys_state *cpuset_css_alloc(struct cgroup *cont)
 {
-        struct cpuset *cs;
-        struct cpuset *parent;
+        struct cgroup *parent_cg = cont->parent;
+        struct cgroup *tmp_cg;
+        struct cpuset *parent, *cs;
 
-        if (!cont->parent) {
+        if (!parent_cg)
                 return &top_cpuset.css;
-        }
-        parent = cgroup_cs(cont->parent);
+        parent = cgroup_cs(parent_cg);
+
         cs = kmalloc(sizeof(*cs), GFP_KERNEL);
         if (!cs)
                 return ERR_PTR(-ENOMEM);
@@ -1855,7 +1819,36 @@ static struct cgroup_subsys_state *cpuset_css_alloc(struct cgroup *cont)
 
         cs->parent = parent;
         number_of_cpusets++;
-        return &cs->css ;
+
+        if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &cont->flags))
+                goto skip_clone;
+
+        /*
+         * Clone @parent's configuration if CGRP_CPUSET_CLONE_CHILDREN is
+         * set.  This flag handling is implemented in cgroup core for
+         * histrical reasons - the flag may be specified during mount.
+         *
+         * Currently, if any sibling cpusets have exclusive cpus or mem, we
+         * refuse to clone the configuration - thereby refusing the task to
+         * be entered, and as a result refusing the sys_unshare() or
+         * clone() which initiated it.  If this becomes a problem for some
+         * users who wish to allow that scenario, then this could be
+         * changed to grant parent->cpus_allowed-sibling_cpus_exclusive
+         * (and likewise for mems) to the new cgroup.
+         */
+        list_for_each_entry(tmp_cg, &parent_cg->children, sibling) {
+                struct cpuset *tmp_cs = cgroup_cs(tmp_cg);
+
+                if (is_mem_exclusive(tmp_cs) || is_cpu_exclusive(tmp_cs))
+                        goto skip_clone;
+        }
+
+        mutex_lock(&callback_mutex);
+        cs->mems_allowed = parent->mems_allowed;
+        cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
+        mutex_unlock(&callback_mutex);
+skip_clone:
+        return &cs->css;
 }
 
 /*
@@ -1882,7 +1875,6 @@ struct cgroup_subsys cpuset_subsys = {
         .css_free = cpuset_css_free,
         .can_attach = cpuset_can_attach,
         .attach = cpuset_attach,
-        .post_clone = cpuset_post_clone,
         .subsys_id = cpuset_subsys_id,
         .base_cftypes = files,
         .early_init = 1,