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1 : : // SPDX-License-Identifier: GPL-2.0-only
2 : : /*
3 : : * async.c: Asynchronous function calls for boot performance
4 : : *
5 : : * (C) Copyright 2009 Intel Corporation
6 : : * Author: Arjan van de Ven <arjan@linux.intel.com>
7 : : */
8 : :
9 : :
10 : : /*
11 : :
12 : : Goals and Theory of Operation
13 : :
14 : : The primary goal of this feature is to reduce the kernel boot time,
15 : : by doing various independent hardware delays and discovery operations
16 : : decoupled and not strictly serialized.
17 : :
18 : : More specifically, the asynchronous function call concept allows
19 : : certain operations (primarily during system boot) to happen
20 : : asynchronously, out of order, while these operations still
21 : : have their externally visible parts happen sequentially and in-order.
22 : : (not unlike how out-of-order CPUs retire their instructions in order)
23 : :
24 : : Key to the asynchronous function call implementation is the concept of
25 : : a "sequence cookie" (which, although it has an abstracted type, can be
26 : : thought of as a monotonically incrementing number).
27 : :
28 : : The async core will assign each scheduled event such a sequence cookie and
29 : : pass this to the called functions.
30 : :
31 : : The asynchronously called function should before doing a globally visible
32 : : operation, such as registering device numbers, call the
33 : : async_synchronize_cookie() function and pass in its own cookie. The
34 : : async_synchronize_cookie() function will make sure that all asynchronous
35 : : operations that were scheduled prior to the operation corresponding with the
36 : : cookie have completed.
37 : :
38 : : Subsystem/driver initialization code that scheduled asynchronous probe
39 : : functions, but which shares global resources with other drivers/subsystems
40 : : that do not use the asynchronous call feature, need to do a full
41 : : synchronization with the async_synchronize_full() function, before returning
42 : : from their init function. This is to maintain strict ordering between the
43 : : asynchronous and synchronous parts of the kernel.
44 : :
45 : : */
46 : :
47 : : #include <linux/async.h>
48 : : #include <linux/atomic.h>
49 : : #include <linux/ktime.h>
50 : : #include <linux/export.h>
51 : : #include <linux/wait.h>
52 : : #include <linux/sched.h>
53 : : #include <linux/slab.h>
54 : : #include <linux/workqueue.h>
55 : :
56 : : #include "workqueue_internal.h"
57 : :
58 : : static async_cookie_t next_cookie = 1;
59 : :
60 : : #define MAX_WORK 32768
61 : : #define ASYNC_COOKIE_MAX ULLONG_MAX /* infinity cookie */
62 : :
63 : : static LIST_HEAD(async_global_pending); /* pending from all registered doms */
64 : : static ASYNC_DOMAIN(async_dfl_domain);
65 : : static DEFINE_SPINLOCK(async_lock);
66 : :
67 : : struct async_entry {
68 : : struct list_head domain_list;
69 : : struct list_head global_list;
70 : : struct work_struct work;
71 : : async_cookie_t cookie;
72 : : async_func_t func;
73 : : void *data;
74 : : struct async_domain *domain;
75 : : };
76 : :
77 : : static DECLARE_WAIT_QUEUE_HEAD(async_done);
78 : :
79 : : static atomic_t entry_count;
80 : :
81 : 621 : static async_cookie_t lowest_in_progress(struct async_domain *domain)
82 : : {
83 : : struct async_entry *first = NULL;
84 : : async_cookie_t ret = ASYNC_COOKIE_MAX;
85 : : unsigned long flags;
86 : :
87 : 621 : spin_lock_irqsave(&async_lock, flags);
88 : :
89 [ - + ]: 621 : if (domain) {
90 [ # # ]: 0 : if (!list_empty(&domain->pending))
91 : 0 : first = list_first_entry(&domain->pending,
92 : : struct async_entry, domain_list);
93 : : } else {
94 [ - + ]: 621 : if (!list_empty(&async_global_pending))
95 : 0 : first = list_first_entry(&async_global_pending,
96 : : struct async_entry, global_list);
97 : : }
98 : :
99 [ - + ]: 621 : if (first)
100 : 0 : ret = first->cookie;
101 : :
102 : : spin_unlock_irqrestore(&async_lock, flags);
103 : 621 : return ret;
104 : : }
105 : :
106 : : /*
107 : : * pick the first pending entry and run it
108 : : */
109 : 0 : static void async_run_entry_fn(struct work_struct *work)
110 : : {
111 : : struct async_entry *entry =
112 : 0 : container_of(work, struct async_entry, work);
113 : : unsigned long flags;
114 : : ktime_t uninitialized_var(calltime), delta, rettime;
115 : :
116 : : /* 1) run (and print duration) */
117 [ # # # # ]: 0 : if (initcall_debug && system_state < SYSTEM_RUNNING) {
118 : : pr_debug("calling %lli_%pS @ %i\n",
119 : : (long long)entry->cookie,
120 : : entry->func, task_pid_nr(current));
121 : 0 : calltime = ktime_get();
122 : : }
123 : 0 : entry->func(entry->data, entry->cookie);
124 [ # # # # ]: 0 : if (initcall_debug && system_state < SYSTEM_RUNNING) {
125 : 0 : rettime = ktime_get();
126 : : delta = ktime_sub(rettime, calltime);
127 : : pr_debug("initcall %lli_%pS returned 0 after %lld usecs\n",
128 : : (long long)entry->cookie,
129 : : entry->func,
130 : : (long long)ktime_to_ns(delta) >> 10);
131 : : }
132 : :
133 : : /* 2) remove self from the pending queues */
134 : 0 : spin_lock_irqsave(&async_lock, flags);
135 : 0 : list_del_init(&entry->domain_list);
136 : 0 : list_del_init(&entry->global_list);
137 : :
138 : : /* 3) free the entry */
139 : 0 : kfree(entry);
140 : : atomic_dec(&entry_count);
141 : :
142 : : spin_unlock_irqrestore(&async_lock, flags);
143 : :
144 : : /* 4) wake up any waiters */
145 : 0 : wake_up(&async_done);
146 : 0 : }
147 : :
148 : : /**
149 : : * async_schedule_node_domain - NUMA specific version of async_schedule_domain
150 : : * @func: function to execute asynchronously
151 : : * @data: data pointer to pass to the function
152 : : * @node: NUMA node that we want to schedule this on or close to
153 : : * @domain: the domain
154 : : *
155 : : * Returns an async_cookie_t that may be used for checkpointing later.
156 : : * @domain may be used in the async_synchronize_*_domain() functions to
157 : : * wait within a certain synchronization domain rather than globally.
158 : : *
159 : : * Note: This function may be called from atomic or non-atomic contexts.
160 : : *
161 : : * The node requested will be honored on a best effort basis. If the node
162 : : * has no CPUs associated with it then the work is distributed among all
163 : : * available CPUs.
164 : : */
165 : 0 : async_cookie_t async_schedule_node_domain(async_func_t func, void *data,
166 : : int node, struct async_domain *domain)
167 : : {
168 : : struct async_entry *entry;
169 : : unsigned long flags;
170 : : async_cookie_t newcookie;
171 : :
172 : : /* allow irq-off callers */
173 : 0 : entry = kzalloc(sizeof(struct async_entry), GFP_ATOMIC);
174 : :
175 : : /*
176 : : * If we're out of memory or if there's too much work
177 : : * pending already, we execute synchronously.
178 : : */
179 [ # # # # ]: 0 : if (!entry || atomic_read(&entry_count) > MAX_WORK) {
180 : 0 : kfree(entry);
181 : 0 : spin_lock_irqsave(&async_lock, flags);
182 : 0 : newcookie = next_cookie++;
183 : : spin_unlock_irqrestore(&async_lock, flags);
184 : :
185 : : /* low on memory.. run synchronously */
186 : 0 : func(data, newcookie);
187 : 0 : return newcookie;
188 : : }
189 : 0 : INIT_LIST_HEAD(&entry->domain_list);
190 : 0 : INIT_LIST_HEAD(&entry->global_list);
191 : 0 : INIT_WORK(&entry->work, async_run_entry_fn);
192 : 0 : entry->func = func;
193 : 0 : entry->data = data;
194 : 0 : entry->domain = domain;
195 : :
196 : 0 : spin_lock_irqsave(&async_lock, flags);
197 : :
198 : : /* allocate cookie and queue */
199 : 0 : newcookie = entry->cookie = next_cookie++;
200 : :
201 : 0 : list_add_tail(&entry->domain_list, &domain->pending);
202 [ # # ]: 0 : if (domain->registered)
203 : : list_add_tail(&entry->global_list, &async_global_pending);
204 : :
205 : : atomic_inc(&entry_count);
206 : : spin_unlock_irqrestore(&async_lock, flags);
207 : :
208 : : /* mark that this task has queued an async job, used by module init */
209 : 0 : current->flags |= PF_USED_ASYNC;
210 : :
211 : : /* schedule for execution */
212 : 0 : queue_work_node(node, system_unbound_wq, &entry->work);
213 : :
214 : 0 : return newcookie;
215 : : }
216 : : EXPORT_SYMBOL_GPL(async_schedule_node_domain);
217 : :
218 : : /**
219 : : * async_schedule_node - NUMA specific version of async_schedule
220 : : * @func: function to execute asynchronously
221 : : * @data: data pointer to pass to the function
222 : : * @node: NUMA node that we want to schedule this on or close to
223 : : *
224 : : * Returns an async_cookie_t that may be used for checkpointing later.
225 : : * Note: This function may be called from atomic or non-atomic contexts.
226 : : *
227 : : * The node requested will be honored on a best effort basis. If the node
228 : : * has no CPUs associated with it then the work is distributed among all
229 : : * available CPUs.
230 : : */
231 : 0 : async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
232 : : {
233 : 0 : return async_schedule_node_domain(func, data, node, &async_dfl_domain);
234 : : }
235 : : EXPORT_SYMBOL_GPL(async_schedule_node);
236 : :
237 : : /**
238 : : * async_synchronize_full - synchronize all asynchronous function calls
239 : : *
240 : : * This function waits until all asynchronous function calls have been done.
241 : : */
242 : 621 : void async_synchronize_full(void)
243 : : {
244 : : async_synchronize_full_domain(NULL);
245 : 621 : }
246 : : EXPORT_SYMBOL_GPL(async_synchronize_full);
247 : :
248 : : /**
249 : : * async_unregister_domain - ensure no more anonymous waiters on this domain
250 : : * @domain: idle domain to flush out of any async_synchronize_full instances
251 : : *
252 : : * async_synchronize_{cookie|full}_domain() are not flushed since callers
253 : : * of these routines should know the lifetime of @domain
254 : : *
255 : : * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
256 : : */
257 : 0 : void async_unregister_domain(struct async_domain *domain)
258 : : {
259 : : spin_lock_irq(&async_lock);
260 [ # # # # : 0 : WARN_ON(!domain->registered || !list_empty(&domain->pending));
# # ]
261 : 0 : domain->registered = 0;
262 : : spin_unlock_irq(&async_lock);
263 : 0 : }
264 : : EXPORT_SYMBOL_GPL(async_unregister_domain);
265 : :
266 : : /**
267 : : * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
268 : : * @domain: the domain to synchronize
269 : : *
270 : : * This function waits until all asynchronous function calls for the
271 : : * synchronization domain specified by @domain have been done.
272 : : */
273 : 0 : void async_synchronize_full_domain(struct async_domain *domain)
274 : : {
275 : 621 : async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
276 : 0 : }
277 : : EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
278 : :
279 : : /**
280 : : * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
281 : : * @cookie: async_cookie_t to use as checkpoint
282 : : * @domain: the domain to synchronize (%NULL for all registered domains)
283 : : *
284 : : * This function waits until all asynchronous function calls for the
285 : : * synchronization domain specified by @domain submitted prior to @cookie
286 : : * have been done.
287 : : */
288 : 621 : void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
289 : : {
290 : : ktime_t uninitialized_var(starttime), delta, endtime;
291 : :
292 [ - + # # ]: 621 : if (initcall_debug && system_state < SYSTEM_RUNNING) {
293 : : pr_debug("async_waiting @ %i\n", task_pid_nr(current));
294 : 0 : starttime = ktime_get();
295 : : }
296 : :
297 [ - + # # ]: 621 : wait_event(async_done, lowest_in_progress(domain) >= cookie);
298 : :
299 [ - + # # ]: 621 : if (initcall_debug && system_state < SYSTEM_RUNNING) {
300 : 0 : endtime = ktime_get();
301 : : delta = ktime_sub(endtime, starttime);
302 : :
303 : : pr_debug("async_continuing @ %i after %lli usec\n",
304 : : task_pid_nr(current),
305 : : (long long)ktime_to_ns(delta) >> 10);
306 : : }
307 : 621 : }
308 : : EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
309 : :
310 : : /**
311 : : * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
312 : : * @cookie: async_cookie_t to use as checkpoint
313 : : *
314 : : * This function waits until all asynchronous function calls prior to @cookie
315 : : * have been done.
316 : : */
317 : 0 : void async_synchronize_cookie(async_cookie_t cookie)
318 : : {
319 : 0 : async_synchronize_cookie_domain(cookie, &async_dfl_domain);
320 : 0 : }
321 : : EXPORT_SYMBOL_GPL(async_synchronize_cookie);
322 : :
323 : : /**
324 : : * current_is_async - is %current an async worker task?
325 : : *
326 : : * Returns %true if %current is an async worker task.
327 : : */
328 : 2277 : bool current_is_async(void)
329 : : {
330 : 2277 : struct worker *worker = current_wq_worker();
331 : :
332 [ - + # # ]: 2277 : return worker && worker->current_func == async_run_entry_fn;
333 : : }
334 : : EXPORT_SYMBOL_GPL(current_is_async);
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