Revert "sched/autogroup: Fix crash on reboot when autogroup is disabled"

This reverts commit 5258f386ea,
because the underlying autogroups bug got fixed upstream in
a better way, via:

  fd8ef11730 Revert "sched, autogroup: Stop going ahead if autogroup is disabled"

Cc: Mike Galbraith <efault@gmx.de>
Cc: Yong Zhang <yong.zhang0@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/auto_group.c

@@ -110,9 +110,6 @@ out_fail:
 
 bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
 {
-	if (!sysctl_sched_autogroup_enabled)
-		return false;
-
 	if (tg != &root_task_group)
 		return false;
 
@@ -146,11 +143,15 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
 
 	p->signal->autogroup = autogroup_kref_get(ag);
 
+	if (!ACCESS_ONCE(sysctl_sched_autogroup_enabled))
+		goto out;
+
 	t = p;
 	do {
 		sched_move_task(t);
 	} while_each_thread(p, t);
 
+out:
 	unlock_task_sighand(p, &flags);
 	autogroup_kref_put(prev);
 }
@@ -158,11 +159,8 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
 /* Allocates GFP_KERNEL, cannot be called under any spinlock */
 void sched_autogroup_create_attach(struct task_struct *p)
 {
-	struct autogroup *ag;
+	struct autogroup *ag = autogroup_create();
 
-	if (!sysctl_sched_autogroup_enabled)
-		return;
-	ag = autogroup_create();
 	autogroup_move_group(p, ag);
 	/* drop extra reference added by autogroup_create() */
 	autogroup_kref_put(ag);
@@ -178,15 +176,11 @@ EXPORT_SYMBOL(sched_autogroup_detach);
 
 void sched_autogroup_fork(struct signal_struct *sig)
 {
-	if (!sysctl_sched_autogroup_enabled)
-		return;
 	sig->autogroup = autogroup_task_get(current);
 }
 
 void sched_autogroup_exit(struct signal_struct *sig)
 {
-	if (!sysctl_sched_autogroup_enabled)
-		return;
 	autogroup_kref_put(sig->autogroup);
 }
 
@@ -199,6 +193,58 @@ static int __init setup_autogroup(char *str)
 
 __setup("noautogroup", setup_autogroup);
 
+#ifdef CONFIG_PROC_FS
+
+int proc_sched_autogroup_set_nice(struct task_struct *p, int nice)
+{
+	static unsigned long next = INITIAL_JIFFIES;
+	struct autogroup *ag;
+	int err;
+
+	if (nice < -20 || nice > 19)
+		return -EINVAL;
+
+	err = security_task_setnice(current, nice);
+	if (err)
+		return err;
+
+	if (nice < 0 && !can_nice(current, nice))
+		return -EPERM;
+
+	/* this is a heavy operation taking global locks.. */
+	if (!capable(CAP_SYS_ADMIN) && time_before(jiffies, next))
+		return -EAGAIN;
+
+	next = HZ / 10 + jiffies;
+	ag = autogroup_task_get(p);
+
+	down_write(&ag->lock);
+	err = sched_group_set_shares(ag->tg, prio_to_weight[nice + 20]);
+	if (!err)
+		ag->nice = nice;
+	up_write(&ag->lock);
+
+	autogroup_kref_put(ag);
+
+	return err;
+}
+
+void proc_sched_autogroup_show_task(struct task_struct *p, struct seq_file *m)
+{
+	struct autogroup *ag = autogroup_task_get(p);
+
+	if (!task_group_is_autogroup(ag->tg))
+		goto out;
+
+	down_read(&ag->lock);
+	seq_printf(m, "/autogroup-%ld nice %d\n", ag->id, ag->nice);
+	up_read(&ag->lock);
+
+out:
+	autogroup_kref_put(ag);
+}
+#endif /* CONFIG_PROC_FS */
+
 #ifdef CONFIG_SCHED_DEBUG
 int autogroup_path(struct task_group *tg, char *buf, int buflen)
 {

kernel/sched/auto_group.h

@@ -4,6 +4,11 @@
 #include <linux/rwsem.h>
 
 struct autogroup {
+	/*
+	 * reference doesn't mean how many thread attach to this
+	 * autogroup now. It just stands for the number of task
+	 * could use this autogroup.
+	 */
 	struct kref		kref;
 	struct task_group	*tg;
 	struct rw_semaphore	lock;
@@ -24,7 +29,9 @@ extern bool task_wants_autogroup(struct task_struct *p, struct task_group *tg);
 static inline struct task_group *
 autogroup_task_group(struct task_struct *p, struct task_group *tg)
 {
-	if (task_wants_autogroup(p, tg))
+	int enabled = ACCESS_ONCE(sysctl_sched_autogroup_enabled);
+
+	if (enabled && task_wants_autogroup(p, tg))
 		return p->signal->autogroup->tg;
 
 	return tg;

kernel/sysctl.c

@@ -367,8 +367,10 @@ static struct ctl_table kern_table[] = {
 		.procname	= "sched_autogroup_enabled",
 		.data		= &sysctl_sched_autogroup_enabled,
 		.maxlen		= sizeof(unsigned int),
-		.mode		= 0444,
-		.proc_handler	= proc_dointvec,
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
 	},
 #endif
 #ifdef CONFIG_CFS_BANDWIDTH