Line data Source code
1 : /* SPDX-License-Identifier: GPL-2.0-only */
2 :
3 : #ifndef WW_RT
4 :
5 : #define MUTEX mutex
6 : #define MUTEX_WAITER mutex_waiter
7 :
8 : static inline struct mutex_waiter *
9 : __ww_waiter_first(struct mutex *lock)
10 : {
11 : struct mutex_waiter *w;
12 :
13 0 : w = list_first_entry(&lock->wait_list, struct mutex_waiter, list);
14 0 : if (list_entry_is_head(w, &lock->wait_list, list))
15 : return NULL;
16 :
17 : return w;
18 : }
19 :
20 : static inline struct mutex_waiter *
21 : __ww_waiter_next(struct mutex *lock, struct mutex_waiter *w)
22 : {
23 0 : w = list_next_entry(w, list);
24 0 : if (list_entry_is_head(w, &lock->wait_list, list))
25 : return NULL;
26 :
27 : return w;
28 : }
29 :
30 : static inline struct mutex_waiter *
31 : __ww_waiter_prev(struct mutex *lock, struct mutex_waiter *w)
32 : {
33 0 : w = list_prev_entry(w, list);
34 0 : if (list_entry_is_head(w, &lock->wait_list, list))
35 : return NULL;
36 :
37 : return w;
38 : }
39 :
40 : static inline struct mutex_waiter *
41 : __ww_waiter_last(struct mutex *lock)
42 : {
43 : struct mutex_waiter *w;
44 :
45 0 : w = list_last_entry(&lock->wait_list, struct mutex_waiter, list);
46 0 : if (list_entry_is_head(w, &lock->wait_list, list))
47 : return NULL;
48 :
49 : return w;
50 : }
51 :
52 : static inline void
53 : __ww_waiter_add(struct mutex *lock, struct mutex_waiter *waiter, struct mutex_waiter *pos)
54 : {
55 0 : struct list_head *p = &lock->wait_list;
56 0 : if (pos)
57 0 : p = &pos->list;
58 0 : __mutex_add_waiter(lock, waiter, p);
59 : }
60 :
61 : static inline struct task_struct *
62 : __ww_mutex_owner(struct mutex *lock)
63 : {
64 0 : return __mutex_owner(lock);
65 : }
66 :
67 : static inline bool
68 : __ww_mutex_has_waiters(struct mutex *lock)
69 : {
70 10 : return atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS;
71 : }
72 :
73 : static inline void lock_wait_lock(struct mutex *lock)
74 : {
75 0 : raw_spin_lock(&lock->wait_lock);
76 : }
77 :
78 : static inline void unlock_wait_lock(struct mutex *lock)
79 : {
80 0 : raw_spin_unlock(&lock->wait_lock);
81 : }
82 :
83 : static inline void lockdep_assert_wait_lock_held(struct mutex *lock)
84 : {
85 : lockdep_assert_held(&lock->wait_lock);
86 : }
87 :
88 : #else /* WW_RT */
89 :
90 : #define MUTEX rt_mutex
91 : #define MUTEX_WAITER rt_mutex_waiter
92 :
93 : static inline struct rt_mutex_waiter *
94 : __ww_waiter_first(struct rt_mutex *lock)
95 : {
96 : struct rb_node *n = rb_first(&lock->rtmutex.waiters.rb_root);
97 : if (!n)
98 : return NULL;
99 : return rb_entry(n, struct rt_mutex_waiter, tree_entry);
100 : }
101 :
102 : static inline struct rt_mutex_waiter *
103 : __ww_waiter_next(struct rt_mutex *lock, struct rt_mutex_waiter *w)
104 : {
105 : struct rb_node *n = rb_next(&w->tree_entry);
106 : if (!n)
107 : return NULL;
108 : return rb_entry(n, struct rt_mutex_waiter, tree_entry);
109 : }
110 :
111 : static inline struct rt_mutex_waiter *
112 : __ww_waiter_prev(struct rt_mutex *lock, struct rt_mutex_waiter *w)
113 : {
114 : struct rb_node *n = rb_prev(&w->tree_entry);
115 : if (!n)
116 : return NULL;
117 : return rb_entry(n, struct rt_mutex_waiter, tree_entry);
118 : }
119 :
120 : static inline struct rt_mutex_waiter *
121 : __ww_waiter_last(struct rt_mutex *lock)
122 : {
123 : struct rb_node *n = rb_last(&lock->rtmutex.waiters.rb_root);
124 : if (!n)
125 : return NULL;
126 : return rb_entry(n, struct rt_mutex_waiter, tree_entry);
127 : }
128 :
129 : static inline void
130 : __ww_waiter_add(struct rt_mutex *lock, struct rt_mutex_waiter *waiter, struct rt_mutex_waiter *pos)
131 : {
132 : /* RT unconditionally adds the waiter first and then removes it on error */
133 : }
134 :
135 : static inline struct task_struct *
136 : __ww_mutex_owner(struct rt_mutex *lock)
137 : {
138 : return rt_mutex_owner(&lock->rtmutex);
139 : }
140 :
141 : static inline bool
142 : __ww_mutex_has_waiters(struct rt_mutex *lock)
143 : {
144 : return rt_mutex_has_waiters(&lock->rtmutex);
145 : }
146 :
147 : static inline void lock_wait_lock(struct rt_mutex *lock)
148 : {
149 : raw_spin_lock(&lock->rtmutex.wait_lock);
150 : }
151 :
152 : static inline void unlock_wait_lock(struct rt_mutex *lock)
153 : {
154 : raw_spin_unlock(&lock->rtmutex.wait_lock);
155 : }
156 :
157 : static inline void lockdep_assert_wait_lock_held(struct rt_mutex *lock)
158 : {
159 : lockdep_assert_held(&lock->rtmutex.wait_lock);
160 : }
161 :
162 : #endif /* WW_RT */
163 :
164 : /*
165 : * Wait-Die:
166 : * The newer transactions are killed when:
167 : * It (the new transaction) makes a request for a lock being held
168 : * by an older transaction.
169 : *
170 : * Wound-Wait:
171 : * The newer transactions are wounded when:
172 : * An older transaction makes a request for a lock being held by
173 : * the newer transaction.
174 : */
175 :
176 : /*
177 : * Associate the ww_mutex @ww with the context @ww_ctx under which we acquired
178 : * it.
179 : */
180 : static __always_inline void
181 : ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
182 : {
183 : #ifdef DEBUG_WW_MUTEXES
184 : /*
185 : * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
186 : * but released with a normal mutex_unlock in this call.
187 : *
188 : * This should never happen, always use ww_mutex_unlock.
189 : */
190 : DEBUG_LOCKS_WARN_ON(ww->ctx);
191 :
192 : /*
193 : * Not quite done after calling ww_acquire_done() ?
194 : */
195 : DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
196 :
197 : if (ww_ctx->contending_lock) {
198 : /*
199 : * After -EDEADLK you tried to
200 : * acquire a different ww_mutex? Bad!
201 : */
202 : DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
203 :
204 : /*
205 : * You called ww_mutex_lock after receiving -EDEADLK,
206 : * but 'forgot' to unlock everything else first?
207 : */
208 : DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
209 : ww_ctx->contending_lock = NULL;
210 : }
211 :
212 : /*
213 : * Naughty, using a different class will lead to undefined behavior!
214 : */
215 : DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
216 : #endif
217 5 : ww_ctx->acquired++;
218 5 : ww->ctx = ww_ctx;
219 : }
220 :
221 : /*
222 : * Determine if @a is 'less' than @b. IOW, either @a is a lower priority task
223 : * or, when of equal priority, a younger transaction than @b.
224 : *
225 : * Depending on the algorithm, @a will either need to wait for @b, or die.
226 : */
227 : static inline bool
228 : __ww_ctx_less(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
229 : {
230 : /*
231 : * Can only do the RT prio for WW_RT, because task->prio isn't stable due to PI,
232 : * so the wait_list ordering will go wobbly. rt_mutex re-queues the waiter and
233 : * isn't affected by this.
234 : */
235 : #ifdef WW_RT
236 : /* kernel prio; less is more */
237 : int a_prio = a->task->prio;
238 : int b_prio = b->task->prio;
239 :
240 : if (rt_prio(a_prio) || rt_prio(b_prio)) {
241 :
242 : if (a_prio > b_prio)
243 : return true;
244 :
245 : if (a_prio < b_prio)
246 : return false;
247 :
248 : /* equal static prio */
249 :
250 : if (dl_prio(a_prio)) {
251 : if (dl_time_before(b->task->dl.deadline,
252 : a->task->dl.deadline))
253 : return true;
254 :
255 : if (dl_time_before(a->task->dl.deadline,
256 : b->task->dl.deadline))
257 : return false;
258 : }
259 :
260 : /* equal prio */
261 : }
262 : #endif
263 :
264 : /* FIFO order tie break -- bigger is younger */
265 0 : return (signed long)(a->stamp - b->stamp) > 0;
266 : }
267 :
268 : /*
269 : * Wait-Die; wake a lesser waiter context (when locks held) such that it can
270 : * die.
271 : *
272 : * Among waiters with context, only the first one can have other locks acquired
273 : * already (ctx->acquired > 0), because __ww_mutex_add_waiter() and
274 : * __ww_mutex_check_kill() wake any but the earliest context.
275 : */
276 : static bool
277 0 : __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
278 : struct ww_acquire_ctx *ww_ctx)
279 : {
280 0 : if (!ww_ctx->is_wait_die)
281 : return false;
282 :
283 0 : if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) {
284 : #ifndef WW_RT
285 : debug_mutex_wake_waiter(lock, waiter);
286 : #endif
287 0 : wake_up_process(waiter->task);
288 : }
289 :
290 : return true;
291 : }
292 :
293 : /*
294 : * Wound-Wait; wound a lesser @hold_ctx if it holds the lock.
295 : *
296 : * Wound the lock holder if there are waiters with more important transactions
297 : * than the lock holders. Even if multiple waiters may wound the lock holder,
298 : * it's sufficient that only one does.
299 : */
300 0 : static bool __ww_mutex_wound(struct MUTEX *lock,
301 : struct ww_acquire_ctx *ww_ctx,
302 : struct ww_acquire_ctx *hold_ctx)
303 : {
304 0 : struct task_struct *owner = __ww_mutex_owner(lock);
305 :
306 0 : lockdep_assert_wait_lock_held(lock);
307 :
308 : /*
309 : * Possible through __ww_mutex_add_waiter() when we race with
310 : * ww_mutex_set_context_fastpath(). In that case we'll get here again
311 : * through __ww_mutex_check_waiters().
312 : */
313 0 : if (!hold_ctx)
314 : return false;
315 :
316 : /*
317 : * Can have !owner because of __mutex_unlock_slowpath(), but if owner,
318 : * it cannot go away because we'll have FLAG_WAITERS set and hold
319 : * wait_lock.
320 : */
321 0 : if (!owner)
322 : return false;
323 :
324 0 : if (ww_ctx->acquired > 0 && __ww_ctx_less(hold_ctx, ww_ctx)) {
325 0 : hold_ctx->wounded = 1;
326 :
327 : /*
328 : * wake_up_process() paired with set_current_state()
329 : * inserts sufficient barriers to make sure @owner either sees
330 : * it's wounded in __ww_mutex_check_kill() or has a
331 : * wakeup pending to re-read the wounded state.
332 : */
333 0 : if (owner != current)
334 0 : wake_up_process(owner);
335 :
336 : return true;
337 : }
338 :
339 : return false;
340 : }
341 :
342 : /*
343 : * We just acquired @lock under @ww_ctx, if there are more important contexts
344 : * waiting behind us on the wait-list, check if they need to die, or wound us.
345 : *
346 : * See __ww_mutex_add_waiter() for the list-order construction; basically the
347 : * list is ordered by stamp, smallest (oldest) first.
348 : *
349 : * This relies on never mixing wait-die/wound-wait on the same wait-list;
350 : * which is currently ensured by that being a ww_class property.
351 : *
352 : * The current task must not be on the wait list.
353 : */
354 : static void
355 0 : __ww_mutex_check_waiters(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
356 : {
357 : struct MUTEX_WAITER *cur;
358 :
359 0 : lockdep_assert_wait_lock_held(lock);
360 :
361 0 : for (cur = __ww_waiter_first(lock); cur;
362 0 : cur = __ww_waiter_next(lock, cur)) {
363 :
364 0 : if (!cur->ww_ctx)
365 0 : continue;
366 :
367 0 : if (__ww_mutex_die(lock, cur, ww_ctx) ||
368 0 : __ww_mutex_wound(lock, cur->ww_ctx, ww_ctx))
369 : break;
370 : }
371 0 : }
372 :
373 : /*
374 : * After acquiring lock with fastpath, where we do not hold wait_lock, set ctx
375 : * and wake up any waiters so they can recheck.
376 : */
377 : static __always_inline void
378 : ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
379 : {
380 5 : ww_mutex_lock_acquired(lock, ctx);
381 :
382 : /*
383 : * The lock->ctx update should be visible on all cores before
384 : * the WAITERS check is done, otherwise contended waiters might be
385 : * missed. The contended waiters will either see ww_ctx == NULL
386 : * and keep spinning, or it will acquire wait_lock, add itself
387 : * to waiter list and sleep.
388 : */
389 5 : smp_mb(); /* See comments above and below. */
390 :
391 : /*
392 : * [W] ww->ctx = ctx [W] MUTEX_FLAG_WAITERS
393 : * MB MB
394 : * [R] MUTEX_FLAG_WAITERS [R] ww->ctx
395 : *
396 : * The memory barrier above pairs with the memory barrier in
397 : * __ww_mutex_add_waiter() and makes sure we either observe ww->ctx
398 : * and/or !empty list.
399 : */
400 10 : if (likely(!__ww_mutex_has_waiters(&lock->base)))
401 : return;
402 :
403 : /*
404 : * Uh oh, we raced in fastpath, check if any of the waiters need to
405 : * die or wound us.
406 : */
407 0 : lock_wait_lock(&lock->base);
408 0 : __ww_mutex_check_waiters(&lock->base, ctx);
409 0 : unlock_wait_lock(&lock->base);
410 : }
411 :
412 : static __always_inline int
413 : __ww_mutex_kill(struct MUTEX *lock, struct ww_acquire_ctx *ww_ctx)
414 : {
415 0 : if (ww_ctx->acquired > 0) {
416 : #ifdef DEBUG_WW_MUTEXES
417 : struct ww_mutex *ww;
418 :
419 : ww = container_of(lock, struct ww_mutex, base);
420 : DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
421 : ww_ctx->contending_lock = ww;
422 : #endif
423 : return -EDEADLK;
424 : }
425 :
426 : return 0;
427 : }
428 :
429 : /*
430 : * Check the wound condition for the current lock acquire.
431 : *
432 : * Wound-Wait: If we're wounded, kill ourself.
433 : *
434 : * Wait-Die: If we're trying to acquire a lock already held by an older
435 : * context, kill ourselves.
436 : *
437 : * Since __ww_mutex_add_waiter() orders the wait-list on stamp, we only have to
438 : * look at waiters before us in the wait-list.
439 : */
440 : static inline int
441 0 : __ww_mutex_check_kill(struct MUTEX *lock, struct MUTEX_WAITER *waiter,
442 : struct ww_acquire_ctx *ctx)
443 : {
444 0 : struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
445 0 : struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
446 : struct MUTEX_WAITER *cur;
447 :
448 0 : if (ctx->acquired == 0)
449 : return 0;
450 :
451 0 : if (!ctx->is_wait_die) {
452 0 : if (ctx->wounded)
453 0 : return __ww_mutex_kill(lock, ctx);
454 :
455 : return 0;
456 : }
457 :
458 0 : if (hold_ctx && __ww_ctx_less(ctx, hold_ctx))
459 : return __ww_mutex_kill(lock, ctx);
460 :
461 : /*
462 : * If there is a waiter in front of us that has a context, then its
463 : * stamp is earlier than ours and we must kill ourself.
464 : */
465 0 : for (cur = __ww_waiter_prev(lock, waiter); cur;
466 0 : cur = __ww_waiter_prev(lock, cur)) {
467 :
468 0 : if (!cur->ww_ctx)
469 0 : continue;
470 :
471 : return __ww_mutex_kill(lock, ctx);
472 : }
473 :
474 : return 0;
475 : }
476 :
477 : /*
478 : * Add @waiter to the wait-list, keep the wait-list ordered by stamp, smallest
479 : * first. Such that older contexts are preferred to acquire the lock over
480 : * younger contexts.
481 : *
482 : * Waiters without context are interspersed in FIFO order.
483 : *
484 : * Furthermore, for Wait-Die kill ourself immediately when possible (there are
485 : * older contexts already waiting) to avoid unnecessary waiting and for
486 : * Wound-Wait ensure we wound the owning context when it is younger.
487 : */
488 : static inline int
489 0 : __ww_mutex_add_waiter(struct MUTEX_WAITER *waiter,
490 : struct MUTEX *lock,
491 : struct ww_acquire_ctx *ww_ctx)
492 : {
493 0 : struct MUTEX_WAITER *cur, *pos = NULL;
494 : bool is_wait_die;
495 :
496 0 : if (!ww_ctx) {
497 : __ww_waiter_add(lock, waiter, NULL);
498 : return 0;
499 : }
500 :
501 0 : is_wait_die = ww_ctx->is_wait_die;
502 :
503 : /*
504 : * Add the waiter before the first waiter with a higher stamp.
505 : * Waiters without a context are skipped to avoid starving
506 : * them. Wait-Die waiters may die here. Wound-Wait waiters
507 : * never die here, but they are sorted in stamp order and
508 : * may wound the lock holder.
509 : */
510 0 : for (cur = __ww_waiter_last(lock); cur;
511 0 : cur = __ww_waiter_prev(lock, cur)) {
512 :
513 0 : if (!cur->ww_ctx)
514 0 : continue;
515 :
516 0 : if (__ww_ctx_less(ww_ctx, cur->ww_ctx)) {
517 : /*
518 : * Wait-Die: if we find an older context waiting, there
519 : * is no point in queueing behind it, as we'd have to
520 : * die the moment it would acquire the lock.
521 : */
522 0 : if (is_wait_die) {
523 0 : int ret = __ww_mutex_kill(lock, ww_ctx);
524 :
525 0 : if (ret)
526 : return ret;
527 : }
528 :
529 : break;
530 : }
531 :
532 0 : pos = cur;
533 :
534 : /* Wait-Die: ensure younger waiters die. */
535 0 : __ww_mutex_die(lock, cur, ww_ctx);
536 : }
537 :
538 0 : __ww_waiter_add(lock, waiter, pos);
539 :
540 : /*
541 : * Wound-Wait: if we're blocking on a mutex owned by a younger context,
542 : * wound that such that we might proceed.
543 : */
544 0 : if (!is_wait_die) {
545 0 : struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
546 :
547 : /*
548 : * See ww_mutex_set_context_fastpath(). Orders setting
549 : * MUTEX_FLAG_WAITERS vs the ww->ctx load,
550 : * such that either we or the fastpath will wound @ww->ctx.
551 : */
552 0 : smp_mb();
553 0 : __ww_mutex_wound(lock, ww_ctx, ww->ctx);
554 : }
555 :
556 : return 0;
557 : }
558 :
559 : static inline void __ww_mutex_unlock(struct ww_mutex *lock)
560 : {
561 5 : if (lock->ctx) {
562 : #ifdef DEBUG_WW_MUTEXES
563 : DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
564 : #endif
565 5 : if (lock->ctx->acquired > 0)
566 5 : lock->ctx->acquired--;
567 5 : lock->ctx = NULL;
568 : }
569 : }
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