[RFC 2/2] cgroup, kthread: cleanup after sticking kthreads to the root cgroup

[Roman Gushchin <guro@fb.com>]

Since we're not allowing to move kernel threads out of the root
cgroup anymore, we don't need some infrastructure built to
introduce partial moving ban by
commit 77f88796cee8 ("cgroup, kthread: close race window where
new kthreads can be migrated to non-root cgroups").

This patch is just a cleanup, no functional change
is performed.

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Mason <clm@fb.com>
Cc: kernel-team@fb.com
Cc: linux-kernel@vger.kernel.org
---
 include/linux/cgroup.h | 21 ---------------------
 include/linux/sched.h  |  4 ----
 kernel/kthread.c       |  2 --
 3 files changed, 27 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 328a70ce0e23..2b2b838beaed 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -626,25 +626,6 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
 	pr_cont_kernfs_path(cgrp->kn);
 }
 
-static inline void cgroup_init_kthreadd(void)
-{
-	/*
-	 * kthreadd is inherited by all kthreads, keep it in the root so
-	 * that the new kthreads are guaranteed to stay in the root until
-	 * initialization is finished.
-	 */
-	current->no_cgroup_migration = 1;
-}
-
-static inline void cgroup_kthread_ready(void)
-{
-	/*
-	 * This kthread finished initialization.  The creator should have
-	 * set PF_NO_SETAFFINITY if this kthread should stay in the root.
-	 */
-	current->no_cgroup_migration = 0;
-}
-
 static inline union kernfs_node_id *cgroup_get_kernfs_id(struct cgroup *cgrp)
 {
 	return &cgrp->kn->id;
@@ -672,8 +653,6 @@ static inline void cgroup_free(struct task_struct *p) {}
 
 static inline int cgroup_init_early(void) { return 0; }
 static inline int cgroup_init(void) { return 0; }
-static inline void cgroup_init_kthreadd(void) {}
-static inline void cgroup_kthread_ready(void) {}
 static inline union kernfs_node_id *cgroup_get_kernfs_id(struct cgroup *cgrp)
 {
 	return NULL;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index bdd6ad6fcce1..7ee7bad521ff 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -650,10 +650,6 @@ struct task_struct {
 #ifdef CONFIG_COMPAT_BRK
 	unsigned			brk_randomized:1;
 #endif
-#ifdef CONFIG_CGROUPS
-	/* disallow userland-initiated cgroup migration */
-	unsigned			no_cgroup_migration:1;
-#endif
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
 
diff --git a/kernel/kthread.c b/kernel/kthread.c
index e92070878ce5..0ba173e9b5b6 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -237,7 +237,6 @@ static int kthread(void *_create)
 
 	ret = -EINTR;
 	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
-		cgroup_kthread_ready();
 		__kthread_parkme(self);
 		ret = threadfn(data);
 	}
@@ -551,7 +550,6 @@ int kthreadd(void *unused)
 	set_mems_allowed(node_states[N_MEMORY]);
 
 	current->flags |= PF_NOFREEZE;
-	cgroup_init_kthreadd();
 
 	for (;;) {
 		set_current_state(TASK_INTERRUPTIBLE);
-- 
2.13.6