kernel/async.c

   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 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         spin_lock_irqsave(&async_lock, flags);
  88
  89         if (domain) {
  90                 if (!list_empty(&domain->pending))
  91                         first = list_first_entry(&domain->pending,
  92                                         struct async_entry, domain_list);
  93         } else {
  94                 if (!list_empty(&async_global_pending))
  95                         first = list_first_entry(&async_global_pending,
  96                                         struct async_entry, global_list);
  97         }
  98
  99         if (first)
 100                 ret = first->cookie;
 101
 102         spin_unlock_irqrestore(&async_lock, flags);
 103         return ret;
 104 }
 105
 106 /*
 107  * pick the first pending entry and run it
 108  */
 109 static void async_run_entry_fn(struct work_struct *work)
 110 {
 111         struct async_entry *entry =
 112                 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         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                 calltime = ktime_get();
 122         }
 123         entry->func(entry->data, entry->cookie);
 124         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 125                 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         spin_lock_irqsave(&async_lock, flags);
 135         list_del_init(&entry->domain_list);
 136         list_del_init(&entry->global_list);
 137
 138         /* 3) free the entry */
 139         kfree(entry);
 140         atomic_dec(&entry_count);
 141
 142         spin_unlock_irqrestore(&async_lock, flags);
 143
 144         /* 4) wake up any waiters */
 145         wake_up(&async_done);
 146 }
 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 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         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         if (!entry || atomic_read(&entry_count) > MAX_WORK) {
 180                 kfree(entry);
 181                 spin_lock_irqsave(&async_lock, flags);
 182                 newcookie = next_cookie++;
 183                 spin_unlock_irqrestore(&async_lock, flags);
 184
 185                 /* low on memory.. run synchronously */
 186                 func(data, newcookie);
 187                 return newcookie;
 188         }
 189         INIT_LIST_HEAD(&entry->domain_list);
 190         INIT_LIST_HEAD(&entry->global_list);
 191         INIT_WORK(&entry->work, async_run_entry_fn);
 192         entry->func = func;
 193         entry->data = data;
 194         entry->domain = domain;
 195
 196         spin_lock_irqsave(&async_lock, flags);
 197
 198         /* allocate cookie and queue */
 199         newcookie = entry->cookie = next_cookie++;
 200
 201         list_add_tail(&entry->domain_list, &domain->pending);
 202         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         /* schedule for execution */
 209         queue_work_node(node, system_unbound_wq, &entry->work);
 210
 211         return newcookie;
 212 }
 213 EXPORT_SYMBOL_GPL(async_schedule_node_domain);
 214
 215 /**
 216  * async_schedule_node - NUMA specific version of async_schedule
 217  * @func: function to execute asynchronously
 218  * @data: data pointer to pass to the function
 219  * @node: NUMA node that we want to schedule this on or close to
 220  *
 221  * Returns an async_cookie_t that may be used for checkpointing later.
 222  * Note: This function may be called from atomic or non-atomic contexts.
 223  *
 224  * The node requested will be honored on a best effort basis. If the node
 225  * has no CPUs associated with it then the work is distributed among all
 226  * available CPUs.
 227  */
 228 async_cookie_t async_schedule_node(async_func_t func, void *data, int node)
 229 {
 230         return async_schedule_node_domain(func, data, node, &async_dfl_domain);
 231 }
 232 EXPORT_SYMBOL_GPL(async_schedule_node);
 233
 234 /**
 235  * async_synchronize_full - synchronize all asynchronous function calls
 236  *
 237  * This function waits until all asynchronous function calls have been done.
 238  */
 239 void async_synchronize_full(void)
 240 {
 241         async_synchronize_full_domain(NULL);
 242 }
 243 EXPORT_SYMBOL_GPL(async_synchronize_full);
 244
 245 /**
 246  * async_unregister_domain - ensure no more anonymous waiters on this domain
 247  * @domain: idle domain to flush out of any async_synchronize_full instances
 248  *
 249  * async_synchronize_{cookie|full}_domain() are not flushed since callers
 250  * of these routines should know the lifetime of @domain
 251  *
 252  * Prefer ASYNC_DOMAIN_EXCLUSIVE() declarations over flushing
 253  */
 254 void async_unregister_domain(struct async_domain *domain)
 255 {
 256         spin_lock_irq(&async_lock);
 257         WARN_ON(!domain->registered || !list_empty(&domain->pending));
 258         domain->registered = 0;
 259         spin_unlock_irq(&async_lock);
 260 }
 261 EXPORT_SYMBOL_GPL(async_unregister_domain);
 262
 263 /**
 264  * async_synchronize_full_domain - synchronize all asynchronous function within a certain domain
 265  * @domain: the domain to synchronize
 266  *
 267  * This function waits until all asynchronous function calls for the
 268  * synchronization domain specified by @domain have been done.
 269  */
 270 void async_synchronize_full_domain(struct async_domain *domain)
 271 {
 272         async_synchronize_cookie_domain(ASYNC_COOKIE_MAX, domain);
 273 }
 274 EXPORT_SYMBOL_GPL(async_synchronize_full_domain);
 275
 276 /**
 277  * async_synchronize_cookie_domain - synchronize asynchronous function calls within a certain domain with cookie checkpointing
 278  * @cookie: async_cookie_t to use as checkpoint
 279  * @domain: the domain to synchronize (%NULL for all registered domains)
 280  *
 281  * This function waits until all asynchronous function calls for the
 282  * synchronization domain specified by @domain submitted prior to @cookie
 283  * have been done.
 284  */
 285 void async_synchronize_cookie_domain(async_cookie_t cookie, struct async_domain *domain)
 286 {
 287         ktime_t uninitialized_var(starttime), delta, endtime;
 288
 289         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 290                 pr_debug("async_waiting @ %i\n", task_pid_nr(current));
 291                 starttime = ktime_get();
 292         }
 293
 294         wait_event(async_done, lowest_in_progress(domain) >= cookie);
 295
 296         if (initcall_debug && system_state < SYSTEM_RUNNING) {
 297                 endtime = ktime_get();
 298                 delta = ktime_sub(endtime, starttime);
 299
 300                 pr_debug("async_continuing @ %i after %lli usec\n",
 301                         task_pid_nr(current),
 302                         (long long)ktime_to_ns(delta) >> 10);
 303         }
 304 }
 305 EXPORT_SYMBOL_GPL(async_synchronize_cookie_domain);
 306
 307 /**
 308  * async_synchronize_cookie - synchronize asynchronous function calls with cookie checkpointing
 309  * @cookie: async_cookie_t to use as checkpoint
 310  *
 311  * This function waits until all asynchronous function calls prior to @cookie
 312  * have been done.
 313  */
 314 void async_synchronize_cookie(async_cookie_t cookie)
 315 {
 316         async_synchronize_cookie_domain(cookie, &async_dfl_domain);
 317 }
 318 EXPORT_SYMBOL_GPL(async_synchronize_cookie);
 319
 320 /**
 321  * current_is_async - is %current an async worker task?
 322  *
 323  * Returns %true if %current is an async worker task.
 324  */
 325 bool current_is_async(void)
 326 {
 327         struct worker *worker = current_wq_worker();
 328
 329         return worker && worker->current_func == async_run_entry_fn;
 330 }
 331 EXPORT_SYMBOL_GPL(current_is_async);