Merge branch 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull SMP hotplug updates from Thomas Gleixner:
 "This update is primarily a cleanup of the CPU hotplug locking code.

  The hotplug locking mechanism is an open coded RWSEM, which allows
  recursive locking. The main problem with that is the recursive nature
  as it evades the full lockdep coverage and hides potential deadlocks.

  The rework replaces the open coded RWSEM with a percpu RWSEM and
  establishes full lockdep coverage that way.

  The bulk of the changes fix up recursive locking issues and address
  the now fully reported potential deadlocks all over the place. Some of
  these deadlocks have been observed in the RT tree, but on mainline the
  probability was low enough to hide them away."

* 'smp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (37 commits)
  cpu/hotplug: Constify attribute_group structures
  powerpc: Only obtain cpu_hotplug_lock if called by rtasd
  ARM/hw_breakpoint: Fix possible recursive locking for arch_hw_breakpoint_init
  cpu/hotplug: Remove unused check_for_tasks() function
  perf/core: Don't release cred_guard_mutex if not taken
  cpuhotplug: Link lock stacks for hotplug callbacks
  acpi/processor: Prevent cpu hotplug deadlock
  sched: Provide is_percpu_thread() helper
  cpu/hotplug: Convert hotplug locking to percpu rwsem
  s390: Prevent hotplug rwsem recursion
  arm: Prevent hotplug rwsem recursion
  arm64: Prevent cpu hotplug rwsem recursion
  kprobes: Cure hotplug lock ordering issues
  jump_label: Reorder hotplug lock and jump_label_lock
  perf/tracing/cpuhotplug: Fix locking order
  ACPI/processor: Use cpu_hotplug_disable() instead of get_online_cpus()
  PCI: Replace the racy recursion prevention
  PCI: Use cpu_hotplug_disable() instead of get_online_cpus()
  perf/x86/intel: Drop get_online_cpus() in intel_snb_check_microcode()
  x86/perf: Drop EXPORT of perf_check_microcode
  ...

1 files changed, 93 insertions, 148 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b86b32ebb3b2..b03a32595cfe 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -27,6 +27,7 @@
 #include <linux/smpboot.h>
 #include <linux/relay.h>
 #include <linux/slab.h>
+#include <linux/percpu-rwsem.h>
 
 #include <trace/events/power.h>
 #define CREATE_TRACE_POINTS
@@ -65,6 +66,12 @@ struct cpuhp_cpu_state {
 
 static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state);
 
+#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
+static struct lock_class_key cpuhp_state_key;
+static struct lockdep_map cpuhp_state_lock_map =
+	STATIC_LOCKDEP_MAP_INIT("cpuhp_state", &cpuhp_state_key);
+#endif
+
 /**
  * cpuhp_step - Hotplug state machine step
  * @name:	Name of the step
@@ -196,121 +203,41 @@ void cpu_maps_update_done(void)
 	mutex_unlock(&cpu_add_remove_lock);
 }
 
-/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
+/*
+ * If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  * Should always be manipulated under cpu_add_remove_lock
  */
 static int cpu_hotplug_disabled;
 
 #ifdef CONFIG_HOTPLUG_CPU
 
-static struct {
-	struct task_struct *active_writer;
-	/* wait queue to wake up the active_writer */
-	wait_queue_head_t wq;
-	/* verifies that no writer will get active while readers are active */
-	struct mutex lock;
-	/*
-	 * Also blocks the new readers during
-	 * an ongoing cpu hotplug operation.
-	 */
-	atomic_t refcount;
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	struct lockdep_map dep_map;
-#endif
-} cpu_hotplug = {
-	.active_writer = NULL,
-	.wq = __WAIT_QUEUE_HEAD_INITIALIZER(cpu_hotplug.wq),
-	.lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-	.dep_map = STATIC_LOCKDEP_MAP_INIT("cpu_hotplug.dep_map", &cpu_hotplug.dep_map),
-#endif
-};
-
-/* Lockdep annotations for get/put_online_cpus() and cpu_hotplug_begin/end() */
-#define cpuhp_lock_acquire_read() lock_map_acquire_read(&cpu_hotplug.dep_map)
-#define cpuhp_lock_acquire_tryread() \
-				  lock_map_acquire_tryread(&cpu_hotplug.dep_map)
-#define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)
-#define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)
+DEFINE_STATIC_PERCPU_RWSEM(cpu_hotplug_lock);
 
-
-void get_online_cpus(void)
+void cpus_read_lock(void)
 {
-	might_sleep();
-	if (cpu_hotplug.active_writer == current)
-		return;
-	cpuhp_lock_acquire_read();
-	mutex_lock(&cpu_hotplug.lock);
-	atomic_inc(&cpu_hotplug.refcount);
-	mutex_unlock(&cpu_hotplug.lock);
+	percpu_down_read(&cpu_hotplug_lock);
 }
-EXPORT_SYMBOL_GPL(get_online_cpus);
+EXPORT_SYMBOL_GPL(cpus_read_lock);
 
-void put_online_cpus(void)
+void cpus_read_unlock(void)
 {
-	int refcount;
-
-	if (cpu_hotplug.active_writer == current)
-		return;
-
-	refcount = atomic_dec_return(&cpu_hotplug.refcount);
-	if (WARN_ON(refcount < 0)) /* try to fix things up */
-		atomic_inc(&cpu_hotplug.refcount);
-
-	if (refcount <= 0 && waitqueue_active(&cpu_hotplug.wq))
-		wake_up(&cpu_hotplug.wq);
-
-	cpuhp_lock_release();
-
+	percpu_up_read(&cpu_hotplug_lock);
 }
-EXPORT_SYMBOL_GPL(put_online_cpus);
+EXPORT_SYMBOL_GPL(cpus_read_unlock);
 
-/*
- * This ensures that the hotplug operation can begin only when the
- * refcount goes to zero.
- *
- * Note that during a cpu-hotplug operation, the new readers, if any,
- * will be blocked by the cpu_hotplug.lock
- *
- * Since cpu_hotplug_begin() is always called after invoking
- * cpu_maps_update_begin(), we can be sure that only one writer is active.
- *
- * Note that theoretically, there is a possibility of a livelock:
- * - Refcount goes to zero, last reader wakes up the sleeping
- *   writer.
- * - Last reader unlocks the cpu_hotplug.lock.
- * - A new reader arrives at this moment, bumps up the refcount.
- * - The writer acquires the cpu_hotplug.lock finds the refcount
- *   non zero and goes to sleep again.
- *
- * However, this is very difficult to achieve in practice since
- * get_online_cpus() not an api which is called all that often.
- *
- */
-void cpu_hotplug_begin(void)
+void cpus_write_lock(void)
 {
-	DEFINE_WAIT(wait);
-
-	cpu_hotplug.active_writer = current;
-	cpuhp_lock_acquire();
+	percpu_down_write(&cpu_hotplug_lock);
+}
 
-	for (;;) {
-		mutex_lock(&cpu_hotplug.lock);
-		prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE);
-		if (likely(!atomic_read(&cpu_hotplug.refcount)))
-				break;
-		mutex_unlock(&cpu_hotplug.lock);
-		schedule();
-	}
-	finish_wait(&cpu_hotplug.wq, &wait);
+void cpus_write_unlock(void)
+{
+	percpu_up_write(&cpu_hotplug_lock);
 }
 
-void cpu_hotplug_done(void)
+void lockdep_assert_cpus_held(void)
 {
-	cpu_hotplug.active_writer = NULL;
-	mutex_unlock(&cpu_hotplug.lock);
-	cpuhp_lock_release();
+	percpu_rwsem_assert_held(&cpu_hotplug_lock);
 }
 
 /*
@@ -344,8 +271,6 @@ void cpu_hotplug_enable(void)
 EXPORT_SYMBOL_GPL(cpu_hotplug_enable);
 #endif	/* CONFIG_HOTPLUG_CPU */
 
-/* Notifier wrappers for transitioning to state machine */
-
 static int bringup_wait_for_ap(unsigned int cpu)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
@@ -484,6 +409,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
 
 	st->should_run = false;
 
+	lock_map_acquire(&cpuhp_state_lock_map);
 	/* Single callback invocation for [un]install ? */
 	if (st->single) {
 		if (st->cb_state < CPUHP_AP_ONLINE) {
@@ -510,6 +436,7 @@ static void cpuhp_thread_fun(unsigned int cpu)
 		else if (st->state > st->target)
 			ret = cpuhp_ap_offline(cpu, st);
 	}
+	lock_map_release(&cpuhp_state_lock_map);
 	st->result = ret;
 	complete(&st->done);
 }
@@ -524,6 +451,9 @@ cpuhp_invoke_ap_callback(int cpu, enum cpuhp_state state, bool bringup,
 	if (!cpu_online(cpu))
 		return 0;
 
+	lock_map_acquire(&cpuhp_state_lock_map);
+	lock_map_release(&cpuhp_state_lock_map);
+
 	/*
 	 * If we are up and running, use the hotplug thread. For early calls
 	 * we invoke the thread function directly.
@@ -567,6 +497,8 @@ static int cpuhp_kick_ap_work(unsigned int cpu)
 	enum cpuhp_state state = st->state;
 
 	trace_cpuhp_enter(cpu, st->target, state, cpuhp_kick_ap_work);
+	lock_map_acquire(&cpuhp_state_lock_map);
+	lock_map_release(&cpuhp_state_lock_map);
 	__cpuhp_kick_ap_work(st);
 	wait_for_completion(&st->done);
 	trace_cpuhp_exit(cpu, st->state, state, st->result);
@@ -630,30 +562,6 @@ void clear_tasks_mm_cpumask(int cpu)
 	rcu_read_unlock();
 }
 
-static inline void check_for_tasks(int dead_cpu)
-{
-	struct task_struct *g, *p;
-
-	read_lock(&tasklist_lock);
-	for_each_process_thread(g, p) {
-		if (!p->on_rq)
-			continue;
-		/*
-		 * We do the check with unlocked task_rq(p)->lock.
-		 * Order the reading to do not warn about a task,
-		 * which was running on this cpu in the past, and
-		 * it's just been woken on another cpu.
-		 */
-		rmb();
-		if (task_cpu(p) != dead_cpu)
-			continue;
-
-		pr_warn("Task %s (pid=%d) is on cpu %d (state=%ld, flags=%x)\n",
-			p->comm, task_pid_nr(p), dead_cpu, p->state, p->flags);
-	}
-	read_unlock(&tasklist_lock);
-}
-
 /* Take this CPU down. */
 static int take_cpu_down(void *_param)
 {
@@ -701,7 +609,7 @@ static int takedown_cpu(unsigned int cpu)
 	/*
 	 * So now all preempt/rcu users must observe !cpu_active().
 	 */
-	err = stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
+	err = stop_machine_cpuslocked(take_cpu_down, NULL, cpumask_of(cpu));
 	if (err) {
 		/* CPU refused to die */
 		irq_unlock_sparse();
@@ -773,7 +681,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
 	if (!cpu_present(cpu))
 		return -EINVAL;
 
-	cpu_hotplug_begin();
+	cpus_write_lock();
 
 	cpuhp_tasks_frozen = tasks_frozen;
 
@@ -811,7 +719,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
 	}
 
 out:
-	cpu_hotplug_done();
+	cpus_write_unlock();
 	return ret;
 }
 
@@ -893,7 +801,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
 	struct task_struct *idle;
 	int ret = 0;
 
-	cpu_hotplug_begin();
+	cpus_write_lock();
 
 	if (!cpu_present(cpu)) {
 		ret = -EINVAL;
@@ -941,7 +849,7 @@ static int _cpu_up(unsigned int cpu, int tasks_frozen, enum cpuhp_state target)
 	target = min((int)target, CPUHP_BRINGUP_CPU);
 	ret = cpuhp_up_callbacks(cpu, st, target);
 out:
-	cpu_hotplug_done();
+	cpus_write_unlock();
 	return ret;
 }
 
@@ -1418,18 +1326,20 @@ static void cpuhp_rollback_install(int failedcpu, enum cpuhp_state state,
 	}
 }
 
-int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
-			       bool invoke)
+int __cpuhp_state_add_instance_cpuslocked(enum cpuhp_state state,
+					  struct hlist_node *node,
+					  bool invoke)
 {
 	struct cpuhp_step *sp;
 	int cpu;
 	int ret;
 
+	lockdep_assert_cpus_held();
+
 	sp = cpuhp_get_step(state);
 	if (sp->multi_instance == false)
 		return -EINVAL;
 
-	get_online_cpus();
 	mutex_lock(&cpuhp_state_mutex);
 
 	if (!invoke || !sp->startup.multi)
@@ -1458,13 +1368,23 @@ add_node:
 	hlist_add_head(node, &sp->list);
 unlock:
 	mutex_unlock(&cpuhp_state_mutex);
-	put_online_cpus();
+	return ret;
+}
+
+int __cpuhp_state_add_instance(enum cpuhp_state state, struct hlist_node *node,
+			       bool invoke)
+{
+	int ret;
+
+	cpus_read_lock();
+	ret = __cpuhp_state_add_instance_cpuslocked(state, node, invoke);
+	cpus_read_unlock();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
 
 /**
- * __cpuhp_setup_state - Setup the callbacks for an hotplug machine state
+ * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
  * @state:		The state to setup
  * @invoke:		If true, the startup function is invoked for cpus where
  *			cpu state >= @state
@@ -1473,25 +1393,27 @@ EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
  * @multi_instance:	State is set up for multiple instances which get
  *			added afterwards.
  *
+ * The caller needs to hold cpus read locked while calling this function.
  * Returns:
  *   On success:
  *      Positive state number if @state is CPUHP_AP_ONLINE_DYN
  *      0 for all other states
  *   On failure: proper (negative) error code
  */
-int __cpuhp_setup_state(enum cpuhp_state state,
-			const char *name, bool invoke,
-			int (*startup)(unsigned int cpu),
-			int (*teardown)(unsigned int cpu),
-			bool multi_instance)
+int __cpuhp_setup_state_cpuslocked(enum cpuhp_state state,
+				   const char *name, bool invoke,
+				   int (*startup)(unsigned int cpu),
+				   int (*teardown)(unsigned int cpu),
+				   bool multi_instance)
 {
 	int cpu, ret = 0;
 	bool dynstate;
 
+	lockdep_assert_cpus_held();
+
 	if (cpuhp_cb_check(state) || !name)
 		return -EINVAL;
 
-	get_online_cpus();
 	mutex_lock(&cpuhp_state_mutex);
 
 	ret = cpuhp_store_callbacks(state, name, startup, teardown,
@@ -1527,7 +1449,6 @@ int __cpuhp_setup_state(enum cpuhp_state state,
 	}
 out:
 	mutex_unlock(&cpuhp_state_mutex);
-	put_online_cpus();
 	/*
 	 * If the requested state is CPUHP_AP_ONLINE_DYN, return the
 	 * dynamically allocated state in case of success.
@@ -1536,6 +1457,22 @@ out:
 		return state;
 	return ret;
 }
+EXPORT_SYMBOL(__cpuhp_setup_state_cpuslocked);
+
+int __cpuhp_setup_state(enum cpuhp_state state,
+			const char *name, bool invoke,
+			int (*startup)(unsigned int cpu),
+			int (*teardown)(unsigned int cpu),
+			bool multi_instance)
+{
+	int ret;
+
+	cpus_read_lock();
+	ret = __cpuhp_setup_state_cpuslocked(state, name, invoke, startup,
+					     teardown, multi_instance);
+	cpus_read_unlock();
+	return ret;
+}
 EXPORT_SYMBOL(__cpuhp_setup_state);
 
 int __cpuhp_state_remove_instance(enum cpuhp_state state,
@@ -1549,7 +1486,7 @@ int __cpuhp_state_remove_instance(enum cpuhp_state state,
 	if (!sp->multi_instance)
 		return -EINVAL;
 
-	get_online_cpus();
+	cpus_read_lock();
 	mutex_lock(&cpuhp_state_mutex);
 
 	if (!invoke || !cpuhp_get_teardown_cb(state))
@@ -1570,29 +1507,30 @@ int __cpuhp_state_remove_instance(enum cpuhp_state state,
 remove:
 	hlist_del(node);
 	mutex_unlock(&cpuhp_state_mutex);
-	put_online_cpus();
+	cpus_read_unlock();
 
 	return 0;
 }
 EXPORT_SYMBOL_GPL(__cpuhp_state_remove_instance);
 
 /**
- * __cpuhp_remove_state - Remove the callbacks for an hotplug machine state
+ * __cpuhp_remove_state_cpuslocked - Remove the callbacks for an hotplug machine state
  * @state:	The state to remove
  * @invoke:	If true, the teardown function is invoked for cpus where
  *		cpu state >= @state
  *
+ * The caller needs to hold cpus read locked while calling this function.
  * The teardown callback is currently not allowed to fail. Think
  * about module removal!
  */
-void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
+void __cpuhp_remove_state_cpuslocked(enum cpuhp_state state, bool invoke)
 {
 	struct cpuhp_step *sp = cpuhp_get_step(state);
 	int cpu;
 
 	BUG_ON(cpuhp_cb_check(state));
 
-	get_online_cpus();
+	lockdep_assert_cpus_held();
 
 	mutex_lock(&cpuhp_state_mutex);
 	if (sp->multi_instance) {
@@ -1620,7 +1558,14 @@ void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
 remove:
 	cpuhp_store_callbacks(state, NULL, NULL, NULL, false);
 	mutex_unlock(&cpuhp_state_mutex);
-	put_online_cpus();
+}
+EXPORT_SYMBOL(__cpuhp_remove_state_cpuslocked);
+
+void __cpuhp_remove_state(enum cpuhp_state state, bool invoke)
+{
+	cpus_read_lock();
+	__cpuhp_remove_state_cpuslocked(state, invoke);
+	cpus_read_unlock();
 }
 EXPORT_SYMBOL(__cpuhp_remove_state);
 
@@ -1689,7 +1634,7 @@ static struct attribute *cpuhp_cpu_attrs[] = {
 	NULL
 };
 
-static struct attribute_group cpuhp_cpu_attr_group = {
+static const struct attribute_group cpuhp_cpu_attr_group = {
 	.attrs = cpuhp_cpu_attrs,
 	.name = "hotplug",
 	NULL
@@ -1721,7 +1666,7 @@ static struct attribute *cpuhp_cpu_root_attrs[] = {
 	NULL
 };
 
-static struct attribute_group cpuhp_cpu_root_attr_group = {
+static const struct attribute_group cpuhp_cpu_root_attr_group = {
 	.attrs = cpuhp_cpu_root_attrs,
 	.name = "hotplug",
 	NULL