cgroup: kill subsys->can_attach_task(), pre_attach() and attach_task()

These three methods are no longer used.  Kill them.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Paul Menage <paul@paulmenage.org>
Cc: Li Zefan <lizf@cn.fujitsu.com>

3 files changed, 5 insertions, 70 deletions

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 8a2f302327fa..a7c96ae5557c 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -615,13 +615,6 @@ fork. If this method returns 0 (success) then this should remain valid
 while the caller holds cgroup_mutex and it is ensured that either
 attach() or cancel_attach() will be called in future.
 
-int can_attach_task(struct cgroup *cgrp, struct task_struct *tsk);
-(cgroup_mutex held by caller)
-
-As can_attach, but for operations that must be run once per task to be
-attached (possibly many when using cgroup_attach_proc). Called after
-can_attach.
-
 void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
                    struct cgroup_taskset *tset)
 (cgroup_mutex held by caller)
@@ -632,12 +625,6 @@ function, so that the subsystem can implement a rollback. If not, not necessary.
 This will be called only about subsystems whose can_attach() operation have
 succeeded. The parameters are identical to can_attach().
 
-void pre_attach(struct cgroup *cgrp);
-(cgroup_mutex held by caller)
-
-For any non-per-thread attachment work that needs to happen before
-attach_task. Needed by cpuset.
-
 void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
             struct cgroup_taskset *tset)
 (cgroup_mutex held by caller)
@@ -646,13 +633,6 @@ Called after the task has been attached to the cgroup, to allow any
 post-attachment activity that requires memory allocations or blocking.
 The parameters are identical to can_attach().
 
-void attach_task(struct cgroup *cgrp, struct task_struct *tsk);
-(cgroup_mutex held by caller)
-
-As attach, but for operations that must be run once per task to be attached,
-like can_attach_task. Called before attach. Currently does not support any
-subsystem that might need the old_cgrp for every thread in the group.
-
 void fork(struct cgroup_subsy *ss, struct task_struct *task)
 
 Called when a task is forked into a cgroup.
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 34256ad9e553..7ad5e406c421 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -490,11 +490,8 @@ struct cgroup_subsys {
         void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
         int (*can_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
                           struct cgroup_taskset *tset);
-        int (*can_attach_task)(struct cgroup *cgrp, struct task_struct *tsk);
         void (*cancel_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
                               struct cgroup_taskset *tset);
-        void (*pre_attach)(struct cgroup *cgrp);
-        void (*attach_task)(struct cgroup *cgrp, struct task_struct *tsk);
         void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
                        struct cgroup_taskset *tset);
         void (*fork)(struct cgroup_subsys *ss, struct task_struct *task);
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 41ee01e392e6..1b3b84174ead 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1944,13 +1944,6 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
                                 goto out;
                         }
                 }
-                if (ss->can_attach_task) {
-                        retval = ss->can_attach_task(cgrp, tsk);
-                        if (retval) {
-                                failed_ss = ss;
-                                goto out;
-                        }
-                }
         }
 
         retval = cgroup_task_migrate(cgrp, oldcgrp, tsk, false);
@@ -1958,10 +1951,6 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
                 goto out;
 
         for_each_subsys(root, ss) {
-                if (ss->pre_attach)
-                        ss->pre_attach(cgrp);
-                if (ss->attach_task)
-                        ss->attach_task(cgrp, tsk);
                 if (ss->attach)
                         ss->attach(ss, cgrp, &tset);
         }
@@ -2093,7 +2082,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
 {
         int retval, i, group_size, nr_migrating_tasks;
         struct cgroup_subsys *ss, *failed_ss = NULL;
-        bool cancel_failed_ss = false;
         /* guaranteed to be initialized later, but the compiler needs this */
         struct css_set *oldcg;
         struct cgroupfs_root *root = cgrp->root;
@@ -2188,21 +2176,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
                                 goto out_cancel_attach;
                         }
                 }
-                /* a callback to be run on every thread in the threadgroup. */
-                if (ss->can_attach_task) {
-                        /* run on each task in the threadgroup. */
-                        for (i = 0; i < group_size; i++) {
-                                tc = flex_array_get(group, i);
-                                if (tc->cgrp == cgrp)
-                                        continue;
-                                retval = ss->can_attach_task(cgrp, tc->task);
-                                if (retval) {
-                                        failed_ss = ss;
-                                        cancel_failed_ss = true;
-                                        goto out_cancel_attach;
-                                }
-                        }
-                }
         }
 
         /*
@@ -2234,15 +2207,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
         }
 
         /*
-         * step 3: now that we're guaranteed success wrt the css_sets, proceed
-         * to move all tasks to the new cgroup, calling ss->attach_task for each
-         * one along the way. there are no failure cases after here, so this is
-         * the commit point.
+         * step 3: now that we're guaranteed success wrt the css_sets,
+         * proceed to move all tasks to the new cgroup.  There are no
+         * failure cases after here, so this is the commit point.
          */
-        for_each_subsys(root, ss) {
-                if (ss->pre_attach)
-                        ss->pre_attach(cgrp);
-        }
         for (i = 0; i < group_size; i++) {
                 tc = flex_array_get(group, i);
                 /* leave current thread as it is if it's already there */
@@ -2250,18 +2218,11 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
                         continue;
                 retval = cgroup_task_migrate(cgrp, tc->cgrp, tc->task, true);
                 BUG_ON(retval);
-                /* attach each task to each subsystem */
-                for_each_subsys(root, ss) {
-                        if (ss->attach_task)
-                                ss->attach_task(cgrp, tc->task);
-                }
         }
         /* nothing is sensitive to fork() after this point. */
 
         /*
-         * step 4: do expensive, non-thread-specific subsystem callbacks.
-         * TODO: if ever a subsystem needs to know the oldcgrp for each task
-         * being moved, this call will need to be reworked to communicate that.
+         * step 4: do subsystem attach callbacks.
          */
         for_each_subsys(root, ss) {
                 if (ss->attach)
@@ -2285,11 +2246,8 @@ out_cancel_attach:
         /* same deal as in cgroup_attach_task */
         if (retval) {
                 for_each_subsys(root, ss) {
-                        if (ss == failed_ss) {
-                                if (cancel_failed_ss && ss->cancel_attach)
-                                        ss->cancel_attach(ss, cgrp, &tset);
+                        if (ss == failed_ss)
                                 break;
-                        }
                         if (ss->cancel_attach)
                                 ss->cancel_attach(ss, cgrp, &tset);
                 }