1 files changed, 346 insertions, 0 deletions
diff --git a/kernel/async.c b/kernel/async.c
new file mode 100644
index 000000000..673bba6bd
--- /dev/null
+++ b/kernel/async.c
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+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * async.c: Asynchronous function calls for boot performance
+ *
+ * (C) Copyright 2009 Intel Corporation
+ * Author: Arjan van de Ven <arjan@linux.intel.com>
+ */
+
+
+/*
+
+Goals and Theory of Operation
+
+The primary goal of this feature is to reduce the kernel boot time,
+by doing various independent hardware delays and discovery operations
+decoupled and not strictly serialized.
+
+More specifically, the asynchronous function call concept allows
+certain operations (primarily during system boot) to happen
+asynchronously, out of order, while these operations still
+have their externally visible parts happen sequentially and in-order.
+(not unlike how out-of-order CPUs retire their instructions in order)
+
+Key to the asynchronous function call implementation is the concept of
+a "sequence cookie" (which, although it has an abstracted type, can be
+thought of as a monotonically incrementing number).
+
+The async core will assign each scheduled event such a sequence cookie and
+pass this to the called functions.
+
+The asynchronously called function should before doing a globally visible
+operation, such as registering device numbers, call the
+async_synchronize_cookie() function and pass in its own cookie. The
+async_synchronize_cookie() function will make sure that all asynchronous
+operations that were scheduled prior to the operation corresponding with the
+cookie have completed.
+
+Subsystem/driver initialization code that scheduled asynchronous probe
+functions, but which shares global resources with other drivers/subsystems
+that do not use the asynchronous call feature, need to do a full
+synchronization with the async_synchronize_full() function, before returning
+from their init function. This is to maintain strict ordering between the
+asynchronous and synchronous parts of the kernel.
+
+*/
+
+#include <linux/async.h>
+#include <linux/atomic.h>
+#include <linux/ktime.h>
+#include <linux/export.h>
+#include <linux/wait.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+
+#include "workqueue_internal.h"
+
+static async_cookie_t next_cookie = 1;
+
+#define MAX_WORK		32768
+#define ASYNC_COOKIE_MAX	ULLONG_MAX	/* infinity cookie */
+
+static LIST_HEAD(async_global_pending);	/* pending from all registered doms */
+static ASYNC_DOMAIN(async_dfl_domain);
+static DEFINE_SPINLOCK(async_lock);
+
+struct async_entry {
+	struct list_head	domain_list;
+	struct list_head	global_list;
+	struct work_struct	work;
+	async_cookie_t		cookie;
+	async_func_t		func;
+	void			*data;
+	struct async_domain	*domain;
+};
+
+static DECLARE_WAIT_QUEUE_HEAD(async_done);
+
+static atomic_t entry_count;
+
+static long long microseconds_since(ktime_t start)
+{
+	ktime_t now = ktime_get();
+	return ktime_to_ns(ktime_sub(now, start)) >> 10;
+}
+
+static async_cookie_t lowest_in_progress(struct async_domain *domain)
+{
+	struct async_entry *first = NULL;
+	async_cookie_t ret = ASYNC_COOKIE_MAX;
+	unsigned long flags;
+
+	spin_lock_irqsave(&async_lock, flags);
+
+	if (domain) {
+		if (!list_empty(&domain->pending))
+			first = list_first_entry(&domain->pending,
+					struct async_entry, domain_list);
+	} else {
+		if (!list_empty(&async_global_pending))
+			first = list_first_entry(&async_global_pending,
+					struct async_entry, global_list);
+	}
+
+	if (first)
+		ret = first->cookie;
+
+	spin_unlock_irqrestore(&async_lock, flags);
+	return ret;
+}
+
+/*
+ * pick the first pending entry and run it
+ */
+static void async_run_entry_fn(struct work_struct *work)
+{
+	struct async_entry *entry =
+		container_of(work, struct async_entry, work);
+	unsigned long flags;
+	ktime_t calltime;
+
+	/* 1) run (and print duration) */
+	pr_debug("calling  %lli_%pS @ %i\n", (long long)entry->cookie,
+		 entry->func, task_pid_nr(current));
+	calltime = ktime_get();
+
+	entry->func(entry->data, entry->cookie);
+
+	pr_debug("initcall %lli_%pS returned after %lld usecs\n",
+		 (long long)entry->cookie, entry->func,
+		 microseconds_since(calltime));
+
+	/* 2) remove self from the pending queues */
+	spin_lock_irqsave(&async_lock, flags);
+	list_del_init(&entry->domain_list);
+	list_del_init(&entry->global_list);
+
+	/* 3) free the entry */
+	kfree(entry);
+	atomic_dec(&entry_count);
+
+	spin_unlock_irqrestore(&async_lock, flags);
+
+	/* 4) wake up any waiters */
+	wake_up(&async_done);
+}
+
+static async_cookie_t __async_schedule_node_domain(async_func_t func,
+						   void *data, int node,
+						   struct async_domain *domain,
+						   struct async_entry *entry)
+{
+	async_cookie_t newcookie;
+	unsigned long flags;
+
+	INIT_LIST_HEAD(&entry->domain_list);
+	INIT_LIST_HEAD(&entry->global_list);
+	INIT_WORK(&entry->work, async_run_entry_fn);
+	entry->func = func;
+	entry->data = data;
+	entry->domain = domain;
+
+	spin_lock_irqsave(&async_lock, flags);
+
+	/* allocate cookie and queue */
+	newcookie = entry->cookie = next_cookie++;
+
+	list_add_tail(&entry->domain_list, &domain->pending);
+	if (domain->registered)
+		list_add_tail(&entry->global_list, &async_global_pending);
+
+	atomic_inc(&entry_count);
+	spin_unlock_irqrestore(&async_lock, flags);
+
+	/* schedule for execution */
+	queue_work_node(node, system_unbound_wq, &entry->work);
+
+	return newcookie;
+}
+
+/**
+ * async_schedule_node_domain - NUMA specific version of async_schedule_domain
+ * @func: function to execute asynchronously
+ * @data: data pointer to pass to the function
+ * @node: NUMA node that we want to schedule this on or close to
+ * @domain: the domain
+ *
+ * Returns an async_cookie_t that may be used for checkpointing later.
+ * @domain may be used in the async_synchronize_*_domain() functions to
+ * wait within a certain synchronization domain rather than globally.
+ *
+ * Note: This function may be called from atomic or non-atomic contexts.
+ *
+ * The node requested will be honored on a best effort basis. If the node
+ * has no CPUs associated with it then the work is distributed among all
+ * available CPUs.
+ */
+async_cookie_t async_schedule_node_domain(async_func_t func, void *data,
+					  int node, struct async_domain *domain)
+{
+	struct async_entry *entry;
+	unsigned long flags;
+	async_cookie_t newcookie;
+
+	/* allow irq-off callers */
+	entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
+
+	/*
+	 * If we're out of memory or if there's too much work
+	 * pending already, we execute synchronously.
+	 */
+	if (!entry || atomic_read(&entry_count) > MAX_WORK) {
+		kfree(entry);
+		spin_lock_irqsave(&async_lock, flags);
+		newcookie = next_cookie++;
+		spin_unlock_irqrestore(&async_lock, flags);
+
+		/* low on memory.. run synchronously */
+		func(data, newcookie);
+		return newcookie;
+	}
+
+	return __async_schedule_node_domain(func, data, node, domain, entry);
+}
+EXPORT_SYMBOL_GPL(async_schedule_node_domain);
+
+/**
+ * async_schedule_node - NUMA specific version of async_schedule
+ * @func: function to execute asynchronously
+ * @data: data pointer to pass to the function
+ * @node: NUMA node that we want to schedule this on or close to
+ *
+ * Returns an async_cookie_t that may be used for checkpointing later.
+ * Note: This function may be called from atomic or non-atomic contexts.
+ *
+ * The node requested will be honored on a best effort basis. If the node
+ * has no CPUs associated with it then the work is distributed among all
+ * available CPUs.
+ */
+async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
+{
+	return async_schedule_node_domain(func, data, node, &async_dfl_domain);
+}
+EXPORT_SYMBOL_GPL(async_schedule_node);
+
+/**
+ * async_schedule_dev_nocall - A simplified variant of async_schedule_dev()
+ * @func: function to execute asynchronously
+ * @dev: device argument to be passed to function
+ *
+ * @dev is used as both the argument for the function and to provide NUMA
+ * context for where to run the function.
+ *
+ * If the asynchronous execution of @func is scheduled successfully, return
+ * true. Otherwise, do nothing and return false, unlike async_schedule_dev()
+ * that will run the function synchronously then.
+ */
+bool async_schedule_dev_nocall(async_func_t func, struct device *dev)
+{
+	struct async_entry *entry;
+
+	entry = kzalloc(sizeof(struct async_entry), GFP_KERNEL);
+
+	/* Give up if there is no memory or too much work. */
+	if (!entry || atomic_read(&entry_count) > MAX_WORK) {
+		kfree(entry);
+		return false;
+	}
+
+	__async_schedule_node_domain(func, dev, dev_to_node(dev),
+				     &async_dfl_domain, entry);
+	return true;
+}
+
+/**
+ * async_synchronize_full - synchronize all asynchronous function calls
+ *
+ * This function waits until all asynchronous function calls have been done.
+ */
+void async_synchronize_full(void)
+{
+	async_synchronize_full_domain(NULL);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_full);
+
+/**
+ * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
+ * @domain: the domain to synchronize
+ *
+ * This function waits until all asynchronous function calls for the
+ * synchronization domain specified by @domain have been done.
+ */
+void async_synchronize_full_domain(struct async_domain *domain)
+{
+	async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
+
+/**
+ * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
+ * @cookie: async_cookie_t to use as checkpoint
+ * @domain: the domain to synchronize (%NULL for all registered domains)
+ *
+ * This function waits until all asynchronous function calls for the
+ * synchronization domain specified by @domain submitted prior to @cookie
+ * have been done.
+ */
+void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
+{
+	ktime_t starttime;
+
+	pr_debug("async_waiting @ %i\n", task_pid_nr(current));
+	starttime = ktime_get();
+
+	wait_event(async_done, lowest_in_progress(domain) >= cookie);
+
+	pr_debug("async_continuing @ %i after %lli usec\n", task_pid_nr(current),
+		 microseconds_since(starttime));
+}
+EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
+
+/**
+ * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
+ * @cookie: async_cookie_t to use as checkpoint
+ *
+ * This function waits until all asynchronous function calls prior to @cookie
+ * have been done.
+ */
+void async_synchronize_cookie(async_cookie_t cookie)
+{
+	async_synchronize_cookie_domain(cookie, &async_dfl_domain);
+}
+EXPORT_SYMBOL_GPL(async_synchronize_cookie);
+
+/**
+ * current_is_async - is %current an async worker task?
+ *
+ * Returns %true if %current is an async worker task.
+ */
+bool current_is_async(void)
+{
+	struct worker *worker = current_wq_worker();
+
+	return worker && worker->current_func == async_run_entry_fn;
+}
+EXPORT_SYMBOL_GPL(current_is_async);