Merge tag 'sched_urgent_for_v5.16_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Borislav Petkov:

 - Avoid touching ~100 config files in order to be able to select the
   preemption model

 - clear cluster CPU masks too, on the CPU unplug path

 - prevent use-after-free in cfs

 - Prevent a race condition when updating CPU cache domains

 - Factor out common shared part of smp_prepare_cpus() into a common
   helper which can be called by both baremetal and Xen, in order to fix
   a booting of Xen PV guests

* tag 'sched_urgent_for_v5.16_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  preempt: Restore preemption model selection configs
  arch_topology: Fix missing clear cluster_cpumask in remove_cpu_topology()
  sched/fair: Prevent dead task groups from regaining cfs_rq's
  sched/core: Mitigate race cpus_share_cache()/update_top_cache_domain()
  x86/smp: Factor out parts of native_smp_prepare_cpus()

6 files changed, 76 insertions, 40 deletions

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 60f1bfc3c7b2..ce77f0265660 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -1,12 +1,23 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+config PREEMPT_NONE_BUILD
+	bool
+
+config PREEMPT_VOLUNTARY_BUILD
+	bool
+
+config PREEMPT_BUILD
+	bool
+	select PREEMPTION
+	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
+
 choice
 	prompt "Preemption Model"
-	default PREEMPT_NONE_BEHAVIOUR
+	default PREEMPT_NONE
 
-config PREEMPT_NONE_BEHAVIOUR
+config PREEMPT_NONE
 	bool "No Forced Preemption (Server)"
-	select PREEMPT_NONE if !PREEMPT_DYNAMIC
+	select PREEMPT_NONE_BUILD if !PREEMPT_DYNAMIC
 	help
 	  This is the traditional Linux preemption model, geared towards
 	  throughput. It will still provide good latencies most of the
@@ -18,10 +29,10 @@ config PREEMPT_NONE_BEHAVIOUR
 	  raw processing power of the kernel, irrespective of scheduling
 	  latencies.
 
-config PREEMPT_VOLUNTARY_BEHAVIOUR
+config PREEMPT_VOLUNTARY
 	bool "Voluntary Kernel Preemption (Desktop)"
 	depends on !ARCH_NO_PREEMPT
-	select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC
+	select PREEMPT_VOLUNTARY_BUILD if !PREEMPT_DYNAMIC
 	help
 	  This option reduces the latency of the kernel by adding more
 	  "explicit preemption points" to the kernel code. These new
@@ -37,10 +48,10 @@ config PREEMPT_VOLUNTARY_BEHAVIOUR
 
 	  Select this if you are building a kernel for a desktop system.
 
-config PREEMPT_BEHAVIOUR
+config PREEMPT
 	bool "Preemptible Kernel (Low-Latency Desktop)"
 	depends on !ARCH_NO_PREEMPT
-	select PREEMPT
+	select PREEMPT_BUILD
 	help
 	  This option reduces the latency of the kernel by making
 	  all kernel code (that is not executing in a critical section)
@@ -58,7 +69,7 @@ config PREEMPT_BEHAVIOUR
 
 config PREEMPT_RT
 	bool "Fully Preemptible Kernel (Real-Time)"
-	depends on EXPERT && ARCH_SUPPORTS_RT && !PREEMPT_DYNAMIC
+	depends on EXPERT && ARCH_SUPPORTS_RT
 	select PREEMPTION
 	help
 	  This option turns the kernel into a real-time kernel by replacing
@@ -75,17 +86,6 @@ config PREEMPT_RT
 
 endchoice
 
-config PREEMPT_NONE
-	bool
-
-config PREEMPT_VOLUNTARY
-	bool
-
-config PREEMPT
-	bool
-	select PREEMPTION
-	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
-
 config PREEMPT_COUNT
        bool
 
@@ -95,8 +95,8 @@ config PREEMPTION
 
 config PREEMPT_DYNAMIC
 	bool "Preemption behaviour defined on boot"
-	depends on HAVE_PREEMPT_DYNAMIC
-	select PREEMPT
+	depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
+	select PREEMPT_BUILD
 	default y
 	help
 	  This option allows to define the preemption model on the kernel
diff --git a/kernel/sched/autogroup.c b/kernel/sched/autogroup.c
index 2067080bb235..8629b37d118e 100644
--- a/kernel/sched/autogroup.c
+++ b/kernel/sched/autogroup.c
@@ -31,7 +31,7 @@ static inline void autogroup_destroy(struct kref *kref)
 	ag->tg->rt_se = NULL;
 	ag->tg->rt_rq = NULL;
 #endif
-	sched_offline_group(ag->tg);
+	sched_release_group(ag->tg);
 	sched_destroy_group(ag->tg);
 }
 
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 523fd602ea90..3c9b0fda64ac 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3726,6 +3726,9 @@ out:
 
 bool cpus_share_cache(int this_cpu, int that_cpu)
 {
+	if (this_cpu == that_cpu)
+		return true;
+
 	return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
 }
 
@@ -6625,13 +6628,13 @@ __setup("preempt=", setup_preempt_mode);
 static void __init preempt_dynamic_init(void)
 {
 	if (preempt_dynamic_mode == preempt_dynamic_undefined) {
-		if (IS_ENABLED(CONFIG_PREEMPT_NONE_BEHAVIOUR)) {
+		if (IS_ENABLED(CONFIG_PREEMPT_NONE)) {
 			sched_dynamic_update(preempt_dynamic_none);
-		} else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY_BEHAVIOUR)) {
+		} else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)) {
 			sched_dynamic_update(preempt_dynamic_voluntary);
 		} else {
 			/* Default static call setting, nothing to do */
-			WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_BEHAVIOUR));
+			WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT));
 			preempt_dynamic_mode = preempt_dynamic_full;
 			pr_info("Dynamic Preempt: full\n");
 		}
@@ -9716,6 +9719,22 @@ static void sched_free_group(struct task_group *tg)
 	kmem_cache_free(task_group_cache, tg);
 }
 
+static void sched_free_group_rcu(struct rcu_head *rcu)
+{
+	sched_free_group(container_of(rcu, struct task_group, rcu));
+}
+
+static void sched_unregister_group(struct task_group *tg)
+{
+	unregister_fair_sched_group(tg);
+	unregister_rt_sched_group(tg);
+	/*
+	 * We have to wait for yet another RCU grace period to expire, as
+	 * print_cfs_stats() might run concurrently.
+	 */
+	call_rcu(&tg->rcu, sched_free_group_rcu);
+}
+
 /* allocate runqueue etc for a new task group */
 struct task_group *sched_create_group(struct task_group *parent)
 {
@@ -9759,25 +9778,35 @@ void sched_online_group(struct task_group *tg, struct task_group *parent)
 }
 
 /* rcu callback to free various structures associated with a task group */
-static void sched_free_group_rcu(struct rcu_head *rhp)
+static void sched_unregister_group_rcu(struct rcu_head *rhp)
 {
 	/* Now it should be safe to free those cfs_rqs: */
-	sched_free_group(container_of(rhp, struct task_group, rcu));
+	sched_unregister_group(container_of(rhp, struct task_group, rcu));
 }
 
 void sched_destroy_group(struct task_group *tg)
 {
 	/* Wait for possible concurrent references to cfs_rqs complete: */
-	call_rcu(&tg->rcu, sched_free_group_rcu);
+	call_rcu(&tg->rcu, sched_unregister_group_rcu);
 }
 
-void sched_offline_group(struct task_group *tg)
+void sched_release_group(struct task_group *tg)
 {
 	unsigned long flags;
 
-	/* End participation in shares distribution: */
-	unregister_fair_sched_group(tg);
-
+	/*
+	 * Unlink first, to avoid walk_tg_tree_from() from finding us (via
+	 * sched_cfs_period_timer()).
+	 *
+	 * For this to be effective, we have to wait for all pending users of
+	 * this task group to leave their RCU critical section to ensure no new
+	 * user will see our dying task group any more. Specifically ensure
+	 * that tg_unthrottle_up() won't add decayed cfs_rq's to it.
+	 *
+	 * We therefore defer calling unregister_fair_sched_group() to
+	 * sched_unregister_group() which is guarantied to get called only after the
+	 * current RCU grace period has expired.
+	 */
 	spin_lock_irqsave(&task_group_lock, flags);
 	list_del_rcu(&tg->list);
 	list_del_rcu(&tg->siblings);
@@ -9896,7 +9925,7 @@ static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
 {
 	struct task_group *tg = css_tg(css);
 
-	sched_offline_group(tg);
+	sched_release_group(tg);
 }
 
 static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
@@ -9906,7 +9935,7 @@ static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
 	/*
 	 * Relies on the RCU grace period between css_released() and this.
 	 */
-	sched_free_group(tg);
+	sched_unregister_group(tg);
 }
 
 /*
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 13950beb01a2..6e476f6d9435 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11456,8 +11456,6 @@ void free_fair_sched_group(struct task_group *tg)
 {
 	int i;
 
-	destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));
-
 	for_each_possible_cpu(i) {
 		if (tg->cfs_rq)
 			kfree(tg->cfs_rq[i]);
@@ -11534,6 +11532,8 @@ void unregister_fair_sched_group(struct task_group *tg)
 	struct rq *rq;
 	int cpu;
 
+	destroy_cfs_bandwidth(tg_cfs_bandwidth(tg));
+
 	for_each_possible_cpu(cpu) {
 		if (tg->se[cpu])
 			remove_entity_load_avg(tg->se[cpu]);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index bb945f8faeca..b48baaba2fc2 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -137,13 +137,17 @@ static inline struct rq *rq_of_rt_se(struct sched_rt_entity *rt_se)
 	return rt_rq->rq;
 }
 
-void free_rt_sched_group(struct task_group *tg)
+void unregister_rt_sched_group(struct task_group *tg)
 {
-	int i;
-
 	if (tg->rt_se)
 		destroy_rt_bandwidth(&tg->rt_bandwidth);
 
+}
+
+void free_rt_sched_group(struct task_group *tg)
+{
+	int i;
+
 	for_each_possible_cpu(i) {
 		if (tg->rt_rq)
 			kfree(tg->rt_rq[i]);
@@ -250,6 +254,8 @@ static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
 	return &rq->rt;
 }
 
+void unregister_rt_sched_group(struct task_group *tg) { }
+
 void free_rt_sched_group(struct task_group *tg) { }
 
 int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 7f1612d26c18..0e66749486e7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -488,6 +488,7 @@ extern void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b);
 extern void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b);
 extern void unthrottle_cfs_rq(struct cfs_rq *cfs_rq);
 
+extern void unregister_rt_sched_group(struct task_group *tg);
 extern void free_rt_sched_group(struct task_group *tg);
 extern int alloc_rt_sched_group(struct task_group *tg, struct task_group *parent);
 extern void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq,
@@ -503,7 +504,7 @@ extern struct task_group *sched_create_group(struct task_group *parent);
 extern void sched_online_group(struct task_group *tg,
 			       struct task_group *parent);
 extern void sched_destroy_group(struct task_group *tg);
-extern void sched_offline_group(struct task_group *tg);
+extern void sched_release_group(struct task_group *tg);
 
 extern void sched_move_task(struct task_struct *tsk);