Merge tag 'smp-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull SMP core updates from Thomas Gleixner:

 - Replace get/put_online_cpus() in various places. The final removal
   will happen shortly before v5.15-rc1 when the rest of the patches
   have been merged.

 - Add debug code to help the analysis of CPU hotplug failures

 - A set of kernel doc updates

* tag 'smp-core-2021-08-30' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  mm: Replace deprecated CPU-hotplug functions.
  md/raid5: Replace deprecated CPU-hotplug functions.
  Documentation: Replace deprecated CPU-hotplug functions.
  smp: Fix all kernel-doc warnings
  cpu/hotplug: Add debug printks for hotplug callback failures
  cpu/hotplug: Use DEVICE_ATTR_*() macro
  cpu/hotplug: Eliminate all kernel-doc warnings
  cpu/hotplug: Fix kernel doc warnings for __cpuhp_setup_state_cpuslocked()
  cpu/hotplug: Fix comment typo
  smpboot: Replace deprecated CPU-hotplug functions.

Author: torvalds

Documentation/core-api/cpu_hotplug.rst

@@ -220,7 +220,7 @@ goes online (offline) and during initial setup (shutdown) of the driver. However
 each registration and removal function is also available with a ``_nocalls``
 suffix which does not invoke the provided callbacks if the invocation of the
 callbacks is not desired. During the manual setup (or teardown) the functions
-``get_online_cpus()`` and ``put_online_cpus()`` should be used to inhibit CPU
+``cpus_read_lock()`` and ``cpus_read_unlock()`` should be used to inhibit CPU
 hotplug operations.
 
 

Documentation/trace/ftrace.rst

@@ -2762,7 +2762,7 @@ listed in:
   put_prev_task_idle
   kmem_cache_create
   pick_next_task_rt
-  get_online_cpus
+  cpus_read_lock
   pick_next_task_fair
   mutex_lock
   [...]

drivers/md/raid5.c

@@ -2437,7 +2437,7 @@ static int resize_chunks(struct r5conf *conf, int new_disks, int new_sectors)
 	    conf->scribble_sectors >= new_sectors)
 		return 0;
 	mddev_suspend(conf->mddev);
-	get_online_cpus();
+	cpus_read_lock();
 
 	for_each_present_cpu(cpu) {
 		struct raid5_percpu *percpu;
@@ -2449,7 +2449,7 @@ static int resize_chunks(struct r5conf *conf, int new_disks, int new_sectors)
 			break;
 	}
 
-	put_online_cpus();
+	cpus_read_unlock();
 	mddev_resume(conf->mddev);
 	if (!err) {
 		conf->scribble_disks = new_disks;

include/linux/cpuhotplug.h

@@ -399,7 +399,7 @@ static inline int cpuhp_state_remove_instance(enum cpuhp_state state,
 
 /**
  * cpuhp_state_remove_instance_nocalls - Remove hotplug instance from state
- *					 without invoking the reatdown callback
+ *					 without invoking the teardown callback
  * @state:	The state from which the instance is removed
  * @node:	The node for this individual state.
  *

kernel/cpu.c

@@ -41,14 +41,19 @@
 #include "smpboot.h"
 
 /**
- * cpuhp_cpu_state - Per cpu hotplug state storage
+ * struct cpuhp_cpu_state - Per cpu hotplug state storage
  * @state:	The current cpu state
  * @target:	The target state
+ * @fail:	Current CPU hotplug callback state
  * @thread:	Pointer to the hotplug thread
  * @should_run:	Thread should execute
  * @rollback:	Perform a rollback
  * @single:	Single callback invocation
  * @bringup:	Single callback bringup or teardown selector
+ * @cpu:	CPU number
+ * @node:	Remote CPU node; for multi-instance, do a
+ *		single entry callback for install/remove
+ * @last:	For multi-instance rollback, remember how far we got
  * @cb_state:	The state for a single callback (install/uninstall)
  * @result:	Result of the operation
  * @done_up:	Signal completion to the issuer of the task for cpu-up
@@ -106,11 +111,12 @@ static inline void cpuhp_lock_release(bool bringup) { }
 #endif
 
 /**
- * cpuhp_step - Hotplug state machine step
+ * struct cpuhp_step - Hotplug state machine step
  * @name:	Name of the step
  * @startup:	Startup function of the step
  * @teardown:	Teardown function of the step
  * @cant_stop:	Bringup/teardown can't be stopped at this step
+ * @multi_instance:	State has multiple instances which get added afterwards
  */
 struct cpuhp_step {
 	const char		*name;
@@ -124,7 +130,9 @@ struct cpuhp_step {
 		int		(*multi)(unsigned int cpu,
 					 struct hlist_node *node);
 	} teardown;
+	/* private: */
 	struct hlist_head	list;
+	/* public: */
 	bool			cant_stop;
 	bool			multi_instance;
 };
@@ -143,14 +151,16 @@ static bool cpuhp_step_empty(bool bringup, struct cpuhp_step *step)
 }
 
 /**
- * cpuhp_invoke_callback _ Invoke the callbacks for a given state
+ * cpuhp_invoke_callback - Invoke the callbacks for a given state
  * @cpu:	The cpu for which the callback should be invoked
  * @state:	The state to do callbacks for
  * @bringup:	True if the bringup callback should be invoked
  * @node:	For multi-instance, do a single entry callback for install/remove
  * @lastp:	For multi-instance rollback, remember how far we got
  *
  * Called from cpu hotplug and from the state register machinery.
+ *
+ * Return: %0 on success or a negative errno code
  */
 static int cpuhp_invoke_callback(unsigned int cpu, enum cpuhp_state state,
 				 bool bringup, struct hlist_node *node,
@@ -682,6 +692,10 @@ static int cpuhp_up_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
 
 	ret = cpuhp_invoke_callback_range(true, cpu, st, target);
 	if (ret) {
+		pr_debug("CPU UP failed (%d) CPU %u state %s (%d)\n",
+			 ret, cpu, cpuhp_get_step(st->state)->name,
+			 st->state);
+
 		cpuhp_reset_state(st, prev_state);
 		if (can_rollback_cpu(st))
 			WARN_ON(cpuhp_invoke_callback_range(false, cpu, st,
@@ -1081,6 +1095,9 @@ static int cpuhp_down_callbacks(unsigned int cpu, struct cpuhp_cpu_state *st,
 
 	ret = cpuhp_invoke_callback_range(false, cpu, st, target);
 	if (ret) {
+		pr_debug("CPU DOWN failed (%d) CPU %u state %s (%d)\n",
+			 ret, cpu, cpuhp_get_step(st->state)->name,
+			 st->state);
 
 		cpuhp_reset_state(st, prev_state);
 
@@ -1183,6 +1200,8 @@ static int cpu_down(unsigned int cpu, enum cpuhp_state target)
  * This function is meant to be used by device core cpu subsystem only.
  *
  * Other subsystems should use remove_cpu() instead.
+ *
+ * Return: %0 on success or a negative errno code
  */
 int cpu_device_down(struct device *dev)
 {
@@ -1395,6 +1414,8 @@ static int cpu_up(unsigned int cpu, enum cpuhp_state target)
  * This function is meant to be used by device core cpu subsystem only.
  *
  * Other subsystems should use add_cpu() instead.
+ *
+ * Return: %0 on success or a negative errno code
  */
 int cpu_device_up(struct device *dev)
 {
@@ -1420,6 +1441,8 @@ EXPORT_SYMBOL_GPL(add_cpu);
  * On some architectures like arm64, we can hibernate on any CPU, but on
  * wake up the CPU we hibernated on might be offline as a side effect of
  * using maxcpus= for example.
+ *
+ * Return: %0 on success or a negative errno code
  */
 int bringup_hibernate_cpu(unsigned int sleep_cpu)
 {
@@ -1976,6 +1999,7 @@ EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
 /**
  * __cpuhp_setup_state_cpuslocked - Setup the callbacks for an hotplug machine state
  * @state:		The state to setup
+ * @name:		Name of the step
  * @invoke:		If true, the startup function is invoked for cpus where
  *			cpu state >= @state
  * @startup:		startup callback function
@@ -1984,9 +2008,9 @@ EXPORT_SYMBOL_GPL(__cpuhp_state_add_instance);
  *			added afterwards.
  *
  * The caller needs to hold cpus read locked while calling this function.
- * Returns:
+ * Return:
  *   On success:
- *      Positive state number if @state is CPUHP_AP_ONLINE_DYN
+ *      Positive state number if @state is CPUHP_AP_ONLINE_DYN;
  *      0 for all other states
  *   On failure: proper (negative) error code
  */
@@ -2232,18 +2256,17 @@ int cpuhp_smt_enable(void)
 #endif
 
 #if defined(CONFIG_SYSFS) && defined(CONFIG_HOTPLUG_CPU)
-static ssize_t show_cpuhp_state(struct device *dev,
-				struct device_attribute *attr, char *buf)
+static ssize_t state_show(struct device *dev,
+			  struct device_attribute *attr, char *buf)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
 	return sprintf(buf, "%d\n", st->state);
 }
-static DEVICE_ATTR(state, 0444, show_cpuhp_state, NULL);
+static DEVICE_ATTR_RO(state);
 
-static ssize_t write_cpuhp_target(struct device *dev,
-				  struct device_attribute *attr,
-				  const char *buf, size_t count)
+static ssize_t target_store(struct device *dev, struct device_attribute *attr,
+			    const char *buf, size_t count)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 	struct cpuhp_step *sp;
@@ -2281,19 +2304,17 @@ static ssize_t write_cpuhp_target(struct device *dev,
 	return ret ? ret : count;
 }
 
-static ssize_t show_cpuhp_target(struct device *dev,
-				 struct device_attribute *attr, char *buf)
+static ssize_t target_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
 	return sprintf(buf, "%d\n", st->target);
 }
-static DEVICE_ATTR(target, 0644, show_cpuhp_target, write_cpuhp_target);
-
+static DEVICE_ATTR_RW(target);
 
-static ssize_t write_cpuhp_fail(struct device *dev,
-				struct device_attribute *attr,
-				const char *buf, size_t count)
+static ssize_t fail_store(struct device *dev, struct device_attribute *attr,
+			  const char *buf, size_t count)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 	struct cpuhp_step *sp;
@@ -2342,15 +2363,15 @@ static ssize_t write_cpuhp_fail(struct device *dev,
 	return count;
 }
 
-static ssize_t show_cpuhp_fail(struct device *dev,
-			       struct device_attribute *attr, char *buf)
+static ssize_t fail_show(struct device *dev,
+			 struct device_attribute *attr, char *buf)
 {
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, dev->id);
 
 	return sprintf(buf, "%d\n", st->fail);
 }
 
-static DEVICE_ATTR(fail, 0644, show_cpuhp_fail, write_cpuhp_fail);
+static DEVICE_ATTR_RW(fail);
 
 static struct attribute *cpuhp_cpu_attrs[] = {
 	&dev_attr_state.attr,
@@ -2365,7 +2386,7 @@ static const struct attribute_group cpuhp_cpu_attr_group = {
 	NULL
 };
 
-static ssize_t show_cpuhp_states(struct device *dev,
+static ssize_t states_show(struct device *dev,
 				 struct device_attribute *attr, char *buf)
 {
 	ssize_t cur, res = 0;
@@ -2384,7 +2405,7 @@ static ssize_t show_cpuhp_states(struct device *dev,
 	mutex_unlock(&cpuhp_state_mutex);
 	return res;
 }
-static DEVICE_ATTR(states, 0444, show_cpuhp_states, NULL);
+static DEVICE_ATTR_RO(states);
 
 static struct attribute *cpuhp_cpu_root_attrs[] = {
 	&dev_attr_states.attr,
@@ -2457,28 +2478,27 @@ static const char *smt_states[] = {
 	[CPU_SMT_NOT_IMPLEMENTED]	= "notimplemented",
 };
 
-static ssize_t
-show_smt_control(struct device *dev, struct device_attribute *attr, char *buf)
+static ssize_t control_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
 {
 	const char *state = smt_states[cpu_smt_control];
 
 	return snprintf(buf, PAGE_SIZE - 2, "%s\n", state);
 }
 
-static ssize_t
-store_smt_control(struct device *dev, struct device_attribute *attr,
-		  const char *buf, size_t count)
+static ssize_t control_store(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t count)
 {
 	return __store_smt_control(dev, attr, buf, count);
 }
-static DEVICE_ATTR(control, 0644, show_smt_control, store_smt_control);
+static DEVICE_ATTR_RW(control);
 
-static ssize_t
-show_smt_active(struct device *dev, struct device_attribute *attr, char *buf)
+static ssize_t active_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
 {
 	return snprintf(buf, PAGE_SIZE - 2, "%d\n", sched_smt_active());
 }
-static DEVICE_ATTR(active, 0444, show_smt_active, NULL);
+static DEVICE_ATTR_RO(active);
 
 static struct attribute *cpuhp_smt_attrs[] = {
 	&dev_attr_control.attr,

kernel/smp.c

@@ -764,7 +764,7 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 EXPORT_SYMBOL(smp_call_function_single);
 
 /**
- * smp_call_function_single_async(): Run an asynchronous function on a
+ * smp_call_function_single_async() - Run an asynchronous function on a
  * 			         specific CPU.
  * @cpu: The CPU to run on.
  * @csd: Pre-allocated and setup data structure
@@ -783,6 +783,8 @@ EXPORT_SYMBOL(smp_call_function_single);
  *
  * NOTE: Be careful, there is unfortunately no current debugging facility to
  * validate the correctness of this serialization.
+ *
+ * Return: %0 on success or negative errno value on error
  */
 int smp_call_function_single_async(int cpu, struct __call_single_data *csd)
 {
@@ -974,7 +976,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
  * @mask: The set of cpus to run on (only runs on online subset).
  * @func: The function to run. This must be fast and non-blocking.
  * @info: An arbitrary pointer to pass to the function.
- * @flags: Bitmask that controls the operation. If %SCF_WAIT is set, wait
+ * @wait: Bitmask that controls the operation. If %SCF_WAIT is set, wait
  *        (atomically) until function has completed on other CPUs. If
  *        %SCF_RUN_LOCAL is set, the function will also be run locally
  *        if the local CPU is set in the @cpumask.
@@ -1180,7 +1182,13 @@ void wake_up_all_idle_cpus(void)
 EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);
 
 /**
- * smp_call_on_cpu - Call a function on a specific cpu
+ * struct smp_call_on_cpu_struct - Call a function on a specific CPU
+ * @work: &work_struct
+ * @done: &completion to signal
+ * @func: function to call
+ * @data: function's data argument
+ * @ret: return value from @func
+ * @cpu: target CPU (%-1 for any CPU)
  *
  * Used to call a function on a specific cpu and wait for it to return.
  * Optionally make sure the call is done on a specified physical cpu via vcpu

kernel/smpboot.c

@@ -291,7 +291,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 	unsigned int cpu;
 	int ret = 0;
 
-	get_online_cpus();
+	cpus_read_lock();
 	mutex_lock(&smpboot_threads_lock);
 	for_each_online_cpu(cpu) {
 		ret = __smpboot_create_thread(plug_thread, cpu);
@@ -304,7 +304,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
 	list_add(&plug_thread->list, &hotplug_threads);
 out:
 	mutex_unlock(&smpboot_threads_lock);
-	put_online_cpus();
+	cpus_read_unlock();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
@@ -317,12 +317,12 @@ EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
  */
 void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
 {
-	get_online_cpus();
+	cpus_read_lock();
 	mutex_lock(&smpboot_threads_lock);
 	list_del(&plug_thread->list);
 	smpboot_destroy_threads(plug_thread);
 	mutex_unlock(&smpboot_threads_lock);
-	put_online_cpus();
+	cpus_read_unlock();
 }
 EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
 

mm/swap_slots.c

@@ -70,9 +70,9 @@ void disable_swap_slots_cache_lock(void)
 	swap_slot_cache_enabled = false;
 	if (swap_slot_cache_initialized) {
 		/* serialize with cpu hotplug operations */
-		get_online_cpus();
+		cpus_read_lock();
 		__drain_swap_slots_cache(SLOTS_CACHE|SLOTS_CACHE_RET);
-		put_online_cpus();
+		cpus_read_unlock();
 	}
 }