Commit | Line | Data |
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457c8996 | 1 | // SPDX-License-Identifier: GPL-2.0-only |
23f78d4a IM |
2 | /* |
3 | * RT-Mutexes: simple blocking mutual exclusion locks with PI support | |
4 | * | |
5 | * started by Ingo Molnar and Thomas Gleixner. | |
6 | * | |
7 | * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> | |
8 | * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> | |
9 | * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt | |
10 | * Copyright (C) 2006 Esben Nielsen | |
992caf7f SR |
11 | * Adaptive Spinlocks: |
12 | * Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich, | |
13 | * and Peter Morreale, | |
14 | * Adaptive Spinlocks simplification: | |
15 | * Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com> | |
d07fe82c | 16 | * |
387b1468 | 17 | * See Documentation/locking/rt-mutex-design.rst for details. |
23f78d4a | 18 | */ |
531ae4b0 TG |
19 | #include <linux/sched.h> |
20 | #include <linux/sched/debug.h> | |
21 | #include <linux/sched/deadline.h> | |
174cd4b1 | 22 | #include <linux/sched/signal.h> |
8bd75c77 | 23 | #include <linux/sched/rt.h> |
84f001e1 | 24 | #include <linux/sched/wake_q.h> |
add46132 | 25 | #include <linux/ww_mutex.h> |
23f78d4a | 26 | |
ee042be1 NK |
27 | #include <trace/events/lock.h> |
28 | ||
23f78d4a IM |
29 | #include "rtmutex_common.h" |
30 | ||
add46132 PZ |
31 | #ifndef WW_RT |
32 | # define build_ww_mutex() (false) | |
33 | # define ww_container_of(rtm) NULL | |
34 | ||
35 | static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter, | |
36 | struct rt_mutex *lock, | |
37 | struct ww_acquire_ctx *ww_ctx) | |
38 | { | |
39 | return 0; | |
40 | } | |
41 | ||
42 | static inline void __ww_mutex_check_waiters(struct rt_mutex *lock, | |
43 | struct ww_acquire_ctx *ww_ctx) | |
44 | { | |
45 | } | |
46 | ||
47 | static inline void ww_mutex_lock_acquired(struct ww_mutex *lock, | |
48 | struct ww_acquire_ctx *ww_ctx) | |
49 | { | |
50 | } | |
51 | ||
52 | static inline int __ww_mutex_check_kill(struct rt_mutex *lock, | |
53 | struct rt_mutex_waiter *waiter, | |
54 | struct ww_acquire_ctx *ww_ctx) | |
55 | { | |
56 | return 0; | |
57 | } | |
58 | ||
59 | #else | |
60 | # define build_ww_mutex() (true) | |
61 | # define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base) | |
62 | # include "ww_mutex.h" | |
63 | #endif | |
64 | ||
23f78d4a IM |
65 | /* |
66 | * lock->owner state tracking: | |
67 | * | |
8161239a LJ |
68 | * lock->owner holds the task_struct pointer of the owner. Bit 0 |
69 | * is used to keep track of the "lock has waiters" state. | |
23f78d4a | 70 | * |
8161239a LJ |
71 | * owner bit0 |
72 | * NULL 0 lock is free (fast acquire possible) | |
73 | * NULL 1 lock is free and has waiters and the top waiter | |
74 | * is going to take the lock* | |
75 | * taskpointer 0 lock is held (fast release possible) | |
76 | * taskpointer 1 lock is held and has waiters** | |
23f78d4a IM |
77 | * |
78 | * The fast atomic compare exchange based acquire and release is only | |
8161239a LJ |
79 | * possible when bit 0 of lock->owner is 0. |
80 | * | |
81 | * (*) It also can be a transitional state when grabbing the lock | |
82 | * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock, | |
83 | * we need to set the bit0 before looking at the lock, and the owner may be | |
84 | * NULL in this small time, hence this can be a transitional state. | |
23f78d4a | 85 | * |
8161239a LJ |
86 | * (**) There is a small time when bit 0 is set but there are no |
87 | * waiters. This can happen when grabbing the lock in the slow path. | |
88 | * To prevent a cmpxchg of the owner releasing the lock, we need to | |
89 | * set this bit before looking at the lock. | |
23f78d4a IM |
90 | */ |
91 | ||
1c0908d8 MG |
92 | static __always_inline struct task_struct * |
93 | rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner) | |
23f78d4a | 94 | { |
8161239a | 95 | unsigned long val = (unsigned long)owner; |
23f78d4a IM |
96 | |
97 | if (rt_mutex_has_waiters(lock)) | |
98 | val |= RT_MUTEX_HAS_WAITERS; | |
99 | ||
1c0908d8 MG |
100 | return (struct task_struct *)val; |
101 | } | |
102 | ||
103 | static __always_inline void | |
104 | rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner) | |
105 | { | |
106 | /* | |
107 | * lock->wait_lock is held but explicit acquire semantics are needed | |
108 | * for a new lock owner so WRITE_ONCE is insufficient. | |
109 | */ | |
110 | xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner)); | |
111 | } | |
112 | ||
113 | static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock) | |
114 | { | |
115 | /* lock->wait_lock is held so the unlock provides release semantics. */ | |
116 | WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL)); | |
23f78d4a IM |
117 | } |
118 | ||
830e6acc | 119 | static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock) |
23f78d4a IM |
120 | { |
121 | lock->owner = (struct task_struct *) | |
122 | ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS); | |
123 | } | |
124 | ||
1c0908d8 MG |
125 | static __always_inline void |
126 | fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock) | |
23f78d4a | 127 | { |
dbb26055 TG |
128 | unsigned long owner, *p = (unsigned long *) &lock->owner; |
129 | ||
130 | if (rt_mutex_has_waiters(lock)) | |
131 | return; | |
132 | ||
133 | /* | |
134 | * The rbtree has no waiters enqueued, now make sure that the | |
135 | * lock->owner still has the waiters bit set, otherwise the | |
136 | * following can happen: | |
137 | * | |
138 | * CPU 0 CPU 1 CPU2 | |
139 | * l->owner=T1 | |
140 | * rt_mutex_lock(l) | |
141 | * lock(l->lock) | |
142 | * l->owner = T1 | HAS_WAITERS; | |
143 | * enqueue(T2) | |
144 | * boost() | |
145 | * unlock(l->lock) | |
146 | * block() | |
147 | * | |
148 | * rt_mutex_lock(l) | |
149 | * lock(l->lock) | |
150 | * l->owner = T1 | HAS_WAITERS; | |
151 | * enqueue(T3) | |
152 | * boost() | |
153 | * unlock(l->lock) | |
154 | * block() | |
155 | * signal(->T2) signal(->T3) | |
156 | * lock(l->lock) | |
157 | * dequeue(T2) | |
158 | * deboost() | |
159 | * unlock(l->lock) | |
160 | * lock(l->lock) | |
161 | * dequeue(T3) | |
162 | * ==> wait list is empty | |
163 | * deboost() | |
164 | * unlock(l->lock) | |
165 | * lock(l->lock) | |
166 | * fixup_rt_mutex_waiters() | |
167 | * if (wait_list_empty(l) { | |
168 | * l->owner = owner | |
169 | * owner = l->owner & ~HAS_WAITERS; | |
170 | * ==> l->owner = T1 | |
171 | * } | |
172 | * lock(l->lock) | |
173 | * rt_mutex_unlock(l) fixup_rt_mutex_waiters() | |
174 | * if (wait_list_empty(l) { | |
175 | * owner = l->owner & ~HAS_WAITERS; | |
176 | * cmpxchg(l->owner, T1, NULL) | |
177 | * ===> Success (l->owner = NULL) | |
178 | * | |
179 | * l->owner = owner | |
180 | * ==> l->owner = T1 | |
181 | * } | |
182 | * | |
183 | * With the check for the waiter bit in place T3 on CPU2 will not | |
184 | * overwrite. All tasks fiddling with the waiters bit are | |
185 | * serialized by l->lock, so nothing else can modify the waiters | |
186 | * bit. If the bit is set then nothing can change l->owner either | |
187 | * so the simple RMW is safe. The cmpxchg() will simply fail if it | |
188 | * happens in the middle of the RMW because the waiters bit is | |
189 | * still set. | |
190 | */ | |
191 | owner = READ_ONCE(*p); | |
1c0908d8 MG |
192 | if (owner & RT_MUTEX_HAS_WAITERS) { |
193 | /* | |
194 | * See rt_mutex_set_owner() and rt_mutex_clear_owner() on | |
195 | * why xchg_acquire() is used for updating owner for | |
196 | * locking and WRITE_ONCE() for unlocking. | |
197 | * | |
198 | * WRITE_ONCE() would work for the acquire case too, but | |
199 | * in case that the lock acquisition failed it might | |
200 | * force other lockers into the slow path unnecessarily. | |
201 | */ | |
202 | if (acquire_lock) | |
203 | xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS); | |
204 | else | |
205 | WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS); | |
206 | } | |
23f78d4a IM |
207 | } |
208 | ||
bd197234 | 209 | /* |
cede8841 SAS |
210 | * We can speed up the acquire/release, if there's no debugging state to be |
211 | * set up. | |
bd197234 | 212 | */ |
cede8841 | 213 | #ifndef CONFIG_DEBUG_RT_MUTEXES |
830e6acc | 214 | static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock, |
78515930 SAS |
215 | struct task_struct *old, |
216 | struct task_struct *new) | |
217 | { | |
709e0b62 | 218 | return try_cmpxchg_acquire(&lock->owner, &old, new); |
78515930 SAS |
219 | } |
220 | ||
af9f0063 SAS |
221 | static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock) |
222 | { | |
223 | return rt_mutex_cmpxchg_acquire(lock, NULL, current); | |
224 | } | |
225 | ||
830e6acc | 226 | static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock, |
78515930 SAS |
227 | struct task_struct *old, |
228 | struct task_struct *new) | |
229 | { | |
709e0b62 | 230 | return try_cmpxchg_release(&lock->owner, &old, new); |
78515930 | 231 | } |
700318d1 DB |
232 | |
233 | /* | |
234 | * Callers must hold the ->wait_lock -- which is the whole purpose as we force | |
235 | * all future threads that attempt to [Rmw] the lock to the slowpath. As such | |
236 | * relaxed semantics suffice. | |
237 | */ | |
830e6acc | 238 | static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock) |
bd197234 | 239 | { |
ce3576eb UB |
240 | unsigned long *p = (unsigned long *) &lock->owner; |
241 | unsigned long owner, new; | |
bd197234 | 242 | |
ce3576eb | 243 | owner = READ_ONCE(*p); |
bd197234 | 244 | do { |
ce3576eb UB |
245 | new = owner | RT_MUTEX_HAS_WAITERS; |
246 | } while (!try_cmpxchg_relaxed(p, &owner, new)); | |
1c0908d8 MG |
247 | |
248 | /* | |
249 | * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE | |
250 | * operations in the event of contention. Ensure the successful | |
251 | * cmpxchg is visible. | |
252 | */ | |
253 | smp_mb__after_atomic(); | |
bd197234 | 254 | } |
27e35715 TG |
255 | |
256 | /* | |
257 | * Safe fastpath aware unlock: | |
258 | * 1) Clear the waiters bit | |
259 | * 2) Drop lock->wait_lock | |
260 | * 3) Try to unlock the lock with cmpxchg | |
261 | */ | |
830e6acc | 262 | static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock, |
d7a2edb8 | 263 | unsigned long flags) |
27e35715 TG |
264 | __releases(lock->wait_lock) |
265 | { | |
266 | struct task_struct *owner = rt_mutex_owner(lock); | |
267 | ||
268 | clear_rt_mutex_waiters(lock); | |
b4abf910 | 269 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
27e35715 TG |
270 | /* |
271 | * If a new waiter comes in between the unlock and the cmpxchg | |
272 | * we have two situations: | |
273 | * | |
274 | * unlock(wait_lock); | |
275 | * lock(wait_lock); | |
276 | * cmpxchg(p, owner, 0) == owner | |
277 | * mark_rt_mutex_waiters(lock); | |
278 | * acquire(lock); | |
279 | * or: | |
280 | * | |
281 | * unlock(wait_lock); | |
282 | * lock(wait_lock); | |
283 | * mark_rt_mutex_waiters(lock); | |
284 | * | |
285 | * cmpxchg(p, owner, 0) != owner | |
286 | * enqueue_waiter(); | |
287 | * unlock(wait_lock); | |
288 | * lock(wait_lock); | |
289 | * wake waiter(); | |
290 | * unlock(wait_lock); | |
291 | * lock(wait_lock); | |
292 | * acquire(lock); | |
293 | */ | |
700318d1 | 294 | return rt_mutex_cmpxchg_release(lock, owner, NULL); |
27e35715 TG |
295 | } |
296 | ||
bd197234 | 297 | #else |
830e6acc | 298 | static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock, |
78515930 SAS |
299 | struct task_struct *old, |
300 | struct task_struct *new) | |
301 | { | |
302 | return false; | |
303 | ||
304 | } | |
305 | ||
af9f0063 SAS |
306 | static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock); |
307 | ||
308 | static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock) | |
309 | { | |
310 | /* | |
311 | * With debug enabled rt_mutex_cmpxchg trylock() will always fail. | |
312 | * | |
313 | * Avoid unconditionally taking the slow path by using | |
314 | * rt_mutex_slow_trylock() which is covered by the debug code and can | |
315 | * acquire a non-contended rtmutex. | |
316 | */ | |
317 | return rt_mutex_slowtrylock(lock); | |
318 | } | |
319 | ||
830e6acc | 320 | static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock, |
78515930 SAS |
321 | struct task_struct *old, |
322 | struct task_struct *new) | |
323 | { | |
324 | return false; | |
325 | } | |
700318d1 | 326 | |
830e6acc | 327 | static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock) |
bd197234 TG |
328 | { |
329 | lock->owner = (struct task_struct *) | |
330 | ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS); | |
331 | } | |
27e35715 TG |
332 | |
333 | /* | |
334 | * Simple slow path only version: lock->owner is protected by lock->wait_lock. | |
335 | */ | |
830e6acc | 336 | static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock, |
d7a2edb8 | 337 | unsigned long flags) |
27e35715 TG |
338 | __releases(lock->wait_lock) |
339 | { | |
340 | lock->owner = NULL; | |
b4abf910 | 341 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
27e35715 TG |
342 | return true; |
343 | } | |
bd197234 TG |
344 | #endif |
345 | ||
715f7f9e PZ |
346 | static __always_inline int __waiter_prio(struct task_struct *task) |
347 | { | |
348 | int prio = task->prio; | |
349 | ||
350 | if (!rt_prio(prio)) | |
351 | return DEFAULT_PRIO; | |
352 | ||
353 | return prio; | |
354 | } | |
355 | ||
f7853c34 PZ |
356 | /* |
357 | * Update the waiter->tree copy of the sort keys. | |
358 | */ | |
715f7f9e PZ |
359 | static __always_inline void |
360 | waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task) | |
361 | { | |
f7853c34 PZ |
362 | lockdep_assert_held(&waiter->lock->wait_lock); |
363 | lockdep_assert(RB_EMPTY_NODE(&waiter->tree.entry)); | |
364 | ||
365 | waiter->tree.prio = __waiter_prio(task); | |
366 | waiter->tree.deadline = task->dl.deadline; | |
367 | } | |
368 | ||
369 | /* | |
370 | * Update the waiter->pi_tree copy of the sort keys (from the tree copy). | |
371 | */ | |
372 | static __always_inline void | |
373 | waiter_clone_prio(struct rt_mutex_waiter *waiter, struct task_struct *task) | |
374 | { | |
375 | lockdep_assert_held(&waiter->lock->wait_lock); | |
376 | lockdep_assert_held(&task->pi_lock); | |
377 | lockdep_assert(RB_EMPTY_NODE(&waiter->pi_tree.entry)); | |
378 | ||
379 | waiter->pi_tree.prio = waiter->tree.prio; | |
380 | waiter->pi_tree.deadline = waiter->tree.deadline; | |
715f7f9e PZ |
381 | } |
382 | ||
19830e55 | 383 | /* |
f7853c34 | 384 | * Only use with rt_waiter_node_{less,equal}() |
19830e55 | 385 | */ |
f7853c34 PZ |
386 | #define task_to_waiter_node(p) \ |
387 | &(struct rt_waiter_node){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline } | |
19830e55 | 388 | #define task_to_waiter(p) \ |
f7853c34 | 389 | &(struct rt_mutex_waiter){ .tree = *task_to_waiter_node(p) } |
19830e55 | 390 | |
f7853c34 PZ |
391 | static __always_inline int rt_waiter_node_less(struct rt_waiter_node *left, |
392 | struct rt_waiter_node *right) | |
fb00aca4 | 393 | { |
2d3d891d | 394 | if (left->prio < right->prio) |
fb00aca4 PZ |
395 | return 1; |
396 | ||
397 | /* | |
2d3d891d DF |
398 | * If both waiters have dl_prio(), we check the deadlines of the |
399 | * associated tasks. | |
400 | * If left waiter has a dl_prio(), and we didn't return 1 above, | |
401 | * then right waiter has a dl_prio() too. | |
fb00aca4 | 402 | */ |
2d3d891d | 403 | if (dl_prio(left->prio)) |
e0aad5b4 | 404 | return dl_time_before(left->deadline, right->deadline); |
fb00aca4 PZ |
405 | |
406 | return 0; | |
407 | } | |
408 | ||
f7853c34 PZ |
409 | static __always_inline int rt_waiter_node_equal(struct rt_waiter_node *left, |
410 | struct rt_waiter_node *right) | |
19830e55 PZ |
411 | { |
412 | if (left->prio != right->prio) | |
413 | return 0; | |
414 | ||
415 | /* | |
416 | * If both waiters have dl_prio(), we check the deadlines of the | |
417 | * associated tasks. | |
418 | * If left waiter has a dl_prio(), and we didn't return 0 above, | |
419 | * then right waiter has a dl_prio() too. | |
420 | */ | |
421 | if (dl_prio(left->prio)) | |
422 | return left->deadline == right->deadline; | |
423 | ||
424 | return 1; | |
425 | } | |
426 | ||
48eb3f4f GH |
427 | static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter, |
428 | struct rt_mutex_waiter *top_waiter) | |
429 | { | |
f7853c34 | 430 | if (rt_waiter_node_less(&waiter->tree, &top_waiter->tree)) |
48eb3f4f GH |
431 | return true; |
432 | ||
433 | #ifdef RT_MUTEX_BUILD_SPINLOCKS | |
434 | /* | |
435 | * Note that RT tasks are excluded from same priority (lateral) | |
436 | * steals to prevent the introduction of an unbounded latency. | |
437 | */ | |
f7853c34 | 438 | if (rt_prio(waiter->tree.prio) || dl_prio(waiter->tree.prio)) |
48eb3f4f GH |
439 | return false; |
440 | ||
f7853c34 | 441 | return rt_waiter_node_equal(&waiter->tree, &top_waiter->tree); |
48eb3f4f GH |
442 | #else |
443 | return false; | |
444 | #endif | |
445 | } | |
446 | ||
5a798725 | 447 | #define __node_2_waiter(node) \ |
f7853c34 | 448 | rb_entry((node), struct rt_mutex_waiter, tree.entry) |
5a798725 | 449 | |
d7a2edb8 | 450 | static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b) |
5a798725 | 451 | { |
add46132 PZ |
452 | struct rt_mutex_waiter *aw = __node_2_waiter(a); |
453 | struct rt_mutex_waiter *bw = __node_2_waiter(b); | |
454 | ||
f7853c34 | 455 | if (rt_waiter_node_less(&aw->tree, &bw->tree)) |
add46132 PZ |
456 | return 1; |
457 | ||
458 | if (!build_ww_mutex()) | |
459 | return 0; | |
460 | ||
f7853c34 | 461 | if (rt_waiter_node_less(&bw->tree, &aw->tree)) |
add46132 PZ |
462 | return 0; |
463 | ||
464 | /* NOTE: relies on waiter->ww_ctx being set before insertion */ | |
465 | if (aw->ww_ctx) { | |
466 | if (!bw->ww_ctx) | |
467 | return 1; | |
468 | ||
469 | return (signed long)(aw->ww_ctx->stamp - | |
470 | bw->ww_ctx->stamp) < 0; | |
471 | } | |
472 | ||
473 | return 0; | |
5a798725 PZ |
474 | } |
475 | ||
d7a2edb8 | 476 | static __always_inline void |
830e6acc | 477 | rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter) |
fb00aca4 | 478 | { |
f7853c34 PZ |
479 | lockdep_assert_held(&lock->wait_lock); |
480 | ||
481 | rb_add_cached(&waiter->tree.entry, &lock->waiters, __waiter_less); | |
fb00aca4 PZ |
482 | } |
483 | ||
d7a2edb8 | 484 | static __always_inline void |
830e6acc | 485 | rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter) |
fb00aca4 | 486 | { |
f7853c34 PZ |
487 | lockdep_assert_held(&lock->wait_lock); |
488 | ||
489 | if (RB_EMPTY_NODE(&waiter->tree.entry)) | |
fb00aca4 PZ |
490 | return; |
491 | ||
f7853c34 PZ |
492 | rb_erase_cached(&waiter->tree.entry, &lock->waiters); |
493 | RB_CLEAR_NODE(&waiter->tree.entry); | |
fb00aca4 PZ |
494 | } |
495 | ||
f7853c34 PZ |
496 | #define __node_2_rt_node(node) \ |
497 | rb_entry((node), struct rt_waiter_node, entry) | |
5a798725 | 498 | |
f7853c34 | 499 | static __always_inline bool __pi_waiter_less(struct rb_node *a, const struct rb_node *b) |
5a798725 | 500 | { |
f7853c34 | 501 | return rt_waiter_node_less(__node_2_rt_node(a), __node_2_rt_node(b)); |
5a798725 PZ |
502 | } |
503 | ||
d7a2edb8 | 504 | static __always_inline void |
fb00aca4 PZ |
505 | rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter) |
506 | { | |
f7853c34 PZ |
507 | lockdep_assert_held(&task->pi_lock); |
508 | ||
509 | rb_add_cached(&waiter->pi_tree.entry, &task->pi_waiters, __pi_waiter_less); | |
fb00aca4 PZ |
510 | } |
511 | ||
d7a2edb8 | 512 | static __always_inline void |
fb00aca4 PZ |
513 | rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter) |
514 | { | |
f7853c34 PZ |
515 | lockdep_assert_held(&task->pi_lock); |
516 | ||
517 | if (RB_EMPTY_NODE(&waiter->pi_tree.entry)) | |
fb00aca4 PZ |
518 | return; |
519 | ||
f7853c34 PZ |
520 | rb_erase_cached(&waiter->pi_tree.entry, &task->pi_waiters); |
521 | RB_CLEAR_NODE(&waiter->pi_tree.entry); | |
fb00aca4 PZ |
522 | } |
523 | ||
f7853c34 PZ |
524 | static __always_inline void rt_mutex_adjust_prio(struct rt_mutex_base *lock, |
525 | struct task_struct *p) | |
c365c292 | 526 | { |
acd58620 | 527 | struct task_struct *pi_task = NULL; |
e96a7705 | 528 | |
f7853c34 PZ |
529 | lockdep_assert_held(&lock->wait_lock); |
530 | lockdep_assert(rt_mutex_owner(lock) == p); | |
acd58620 | 531 | lockdep_assert_held(&p->pi_lock); |
c365c292 | 532 | |
acd58620 PZ |
533 | if (task_has_pi_waiters(p)) |
534 | pi_task = task_top_pi_waiter(p)->task; | |
c365c292 | 535 | |
acd58620 | 536 | rt_mutex_setprio(p, pi_task); |
23f78d4a IM |
537 | } |
538 | ||
b576e640 | 539 | /* RT mutex specific wake_q wrappers */ |
9321f815 TG |
540 | static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh, |
541 | struct task_struct *task, | |
542 | unsigned int wake_state) | |
b576e640 | 543 | { |
9321f815 | 544 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) { |
456cfbc6 TG |
545 | if (IS_ENABLED(CONFIG_PROVE_LOCKING)) |
546 | WARN_ON_ONCE(wqh->rtlock_task); | |
9321f815 TG |
547 | get_task_struct(task); |
548 | wqh->rtlock_task = task; | |
456cfbc6 | 549 | } else { |
9321f815 | 550 | wake_q_add(&wqh->head, task); |
456cfbc6 | 551 | } |
b576e640 TG |
552 | } |
553 | ||
9321f815 TG |
554 | static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh, |
555 | struct rt_mutex_waiter *w) | |
556 | { | |
557 | rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state); | |
558 | } | |
559 | ||
b576e640 TG |
560 | static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh) |
561 | { | |
456cfbc6 TG |
562 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) { |
563 | wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT); | |
564 | put_task_struct(wqh->rtlock_task); | |
565 | wqh->rtlock_task = NULL; | |
566 | } | |
567 | ||
568 | if (!wake_q_empty(&wqh->head)) | |
569 | wake_up_q(&wqh->head); | |
b576e640 TG |
570 | |
571 | /* Pairs with preempt_disable() in mark_wakeup_next_waiter() */ | |
572 | preempt_enable(); | |
573 | } | |
574 | ||
8930ed80 TG |
575 | /* |
576 | * Deadlock detection is conditional: | |
577 | * | |
578 | * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted | |
579 | * if the detect argument is == RT_MUTEX_FULL_CHAINWALK. | |
580 | * | |
581 | * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always | |
582 | * conducted independent of the detect argument. | |
583 | * | |
584 | * If the waiter argument is NULL this indicates the deboost path and | |
585 | * deadlock detection is disabled independent of the detect argument | |
586 | * and the config settings. | |
587 | */ | |
d7a2edb8 TG |
588 | static __always_inline bool |
589 | rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter, | |
590 | enum rtmutex_chainwalk chwalk) | |
8930ed80 | 591 | { |
07d25971 | 592 | if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES)) |
f7efc479 TG |
593 | return waiter != NULL; |
594 | return chwalk == RT_MUTEX_FULL_CHAINWALK; | |
8930ed80 TG |
595 | } |
596 | ||
830e6acc | 597 | static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p) |
82084984 TG |
598 | { |
599 | return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL; | |
600 | } | |
601 | ||
23f78d4a IM |
602 | /* |
603 | * Adjust the priority chain. Also used for deadlock detection. | |
604 | * Decreases task's usage by one - may thus free the task. | |
0c106173 | 605 | * |
82084984 TG |
606 | * @task: the task owning the mutex (owner) for which a chain walk is |
607 | * probably needed | |
e6beaa36 | 608 | * @chwalk: do we have to carry out deadlock detection? |
82084984 TG |
609 | * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck |
610 | * things for a task that has just got its priority adjusted, and | |
611 | * is waiting on a mutex) | |
612 | * @next_lock: the mutex on which the owner of @orig_lock was blocked before | |
613 | * we dropped its pi_lock. Is never dereferenced, only used for | |
614 | * comparison to detect lock chain changes. | |
0c106173 | 615 | * @orig_waiter: rt_mutex_waiter struct for the task that has just donated |
82084984 TG |
616 | * its priority to the mutex owner (can be NULL in the case |
617 | * depicted above or if the top waiter is gone away and we are | |
618 | * actually deboosting the owner) | |
619 | * @top_task: the current top waiter | |
0c106173 | 620 | * |
23f78d4a | 621 | * Returns 0 or -EDEADLK. |
3eb65aea TG |
622 | * |
623 | * Chain walk basics and protection scope | |
624 | * | |
625 | * [R] refcount on task | |
f7853c34 | 626 | * [Pn] task->pi_lock held |
3eb65aea TG |
627 | * [L] rtmutex->wait_lock held |
628 | * | |
f7853c34 PZ |
629 | * Normal locking order: |
630 | * | |
631 | * rtmutex->wait_lock | |
632 | * task->pi_lock | |
633 | * | |
3eb65aea TG |
634 | * Step Description Protected by |
635 | * function arguments: | |
636 | * @task [R] | |
637 | * @orig_lock if != NULL @top_task is blocked on it | |
638 | * @next_lock Unprotected. Cannot be | |
639 | * dereferenced. Only used for | |
640 | * comparison. | |
641 | * @orig_waiter if != NULL @top_task is blocked on it | |
642 | * @top_task current, or in case of proxy | |
643 | * locking protected by calling | |
644 | * code | |
645 | * again: | |
646 | * loop_sanity_check(); | |
647 | * retry: | |
f7853c34 PZ |
648 | * [1] lock(task->pi_lock); [R] acquire [P1] |
649 | * [2] waiter = task->pi_blocked_on; [P1] | |
650 | * [3] check_exit_conditions_1(); [P1] | |
651 | * [4] lock = waiter->lock; [P1] | |
652 | * [5] if (!try_lock(lock->wait_lock)) { [P1] try to acquire [L] | |
653 | * unlock(task->pi_lock); release [P1] | |
3eb65aea TG |
654 | * goto retry; |
655 | * } | |
f7853c34 PZ |
656 | * [6] check_exit_conditions_2(); [P1] + [L] |
657 | * [7] requeue_lock_waiter(lock, waiter); [P1] + [L] | |
658 | * [8] unlock(task->pi_lock); release [P1] | |
3eb65aea TG |
659 | * put_task_struct(task); release [R] |
660 | * [9] check_exit_conditions_3(); [L] | |
661 | * [10] task = owner(lock); [L] | |
662 | * get_task_struct(task); [L] acquire [R] | |
f7853c34 PZ |
663 | * lock(task->pi_lock); [L] acquire [P2] |
664 | * [11] requeue_pi_waiter(tsk, waiters(lock));[P2] + [L] | |
665 | * [12] check_exit_conditions_4(); [P2] + [L] | |
666 | * [13] unlock(task->pi_lock); release [P2] | |
3eb65aea TG |
667 | * unlock(lock->wait_lock); release [L] |
668 | * goto again; | |
f7853c34 PZ |
669 | * |
670 | * Where P1 is the blocking task and P2 is the lock owner; going up one step | |
671 | * the owner becomes the next blocked task etc.. | |
672 | * | |
673 | * | |
23f78d4a | 674 | */ |
d7a2edb8 TG |
675 | static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task, |
676 | enum rtmutex_chainwalk chwalk, | |
830e6acc PZ |
677 | struct rt_mutex_base *orig_lock, |
678 | struct rt_mutex_base *next_lock, | |
d7a2edb8 TG |
679 | struct rt_mutex_waiter *orig_waiter, |
680 | struct task_struct *top_task) | |
23f78d4a | 681 | { |
23f78d4a | 682 | struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter; |
a57594a1 | 683 | struct rt_mutex_waiter *prerequeue_top_waiter; |
8930ed80 | 684 | int ret = 0, depth = 0; |
830e6acc | 685 | struct rt_mutex_base *lock; |
8930ed80 | 686 | bool detect_deadlock; |
67792e2c | 687 | bool requeue = true; |
23f78d4a | 688 | |
8930ed80 | 689 | detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk); |
23f78d4a IM |
690 | |
691 | /* | |
692 | * The (de)boosting is a step by step approach with a lot of | |
693 | * pitfalls. We want this to be preemptible and we want hold a | |
694 | * maximum of two locks per step. So we have to check | |
695 | * carefully whether things change under us. | |
696 | */ | |
697 | again: | |
3eb65aea TG |
698 | /* |
699 | * We limit the lock chain length for each invocation. | |
700 | */ | |
23f78d4a IM |
701 | if (++depth > max_lock_depth) { |
702 | static int prev_max; | |
703 | ||
704 | /* | |
705 | * Print this only once. If the admin changes the limit, | |
706 | * print a new message when reaching the limit again. | |
707 | */ | |
708 | if (prev_max != max_lock_depth) { | |
709 | prev_max = max_lock_depth; | |
710 | printk(KERN_WARNING "Maximum lock depth %d reached " | |
711 | "task: %s (%d)\n", max_lock_depth, | |
ba25f9dc | 712 | top_task->comm, task_pid_nr(top_task)); |
23f78d4a IM |
713 | } |
714 | put_task_struct(task); | |
715 | ||
3d5c9340 | 716 | return -EDEADLK; |
23f78d4a | 717 | } |
3eb65aea TG |
718 | |
719 | /* | |
720 | * We are fully preemptible here and only hold the refcount on | |
721 | * @task. So everything can have changed under us since the | |
722 | * caller or our own code below (goto retry/again) dropped all | |
723 | * locks. | |
724 | */ | |
23f78d4a IM |
725 | retry: |
726 | /* | |
3eb65aea | 727 | * [1] Task cannot go away as we did a get_task() before ! |
23f78d4a | 728 | */ |
b4abf910 | 729 | raw_spin_lock_irq(&task->pi_lock); |
23f78d4a | 730 | |
3eb65aea TG |
731 | /* |
732 | * [2] Get the waiter on which @task is blocked on. | |
733 | */ | |
23f78d4a | 734 | waiter = task->pi_blocked_on; |
3eb65aea TG |
735 | |
736 | /* | |
737 | * [3] check_exit_conditions_1() protected by task->pi_lock. | |
738 | */ | |
739 | ||
23f78d4a IM |
740 | /* |
741 | * Check whether the end of the boosting chain has been | |
742 | * reached or the state of the chain has changed while we | |
743 | * dropped the locks. | |
744 | */ | |
8161239a | 745 | if (!waiter) |
23f78d4a IM |
746 | goto out_unlock_pi; |
747 | ||
1a539a87 TG |
748 | /* |
749 | * Check the orig_waiter state. After we dropped the locks, | |
8161239a | 750 | * the previous owner of the lock might have released the lock. |
1a539a87 | 751 | */ |
8161239a | 752 | if (orig_waiter && !rt_mutex_owner(orig_lock)) |
1a539a87 TG |
753 | goto out_unlock_pi; |
754 | ||
82084984 TG |
755 | /* |
756 | * We dropped all locks after taking a refcount on @task, so | |
757 | * the task might have moved on in the lock chain or even left | |
758 | * the chain completely and blocks now on an unrelated lock or | |
759 | * on @orig_lock. | |
760 | * | |
761 | * We stored the lock on which @task was blocked in @next_lock, | |
762 | * so we can detect the chain change. | |
763 | */ | |
764 | if (next_lock != waiter->lock) | |
765 | goto out_unlock_pi; | |
766 | ||
6467822b PZ |
767 | /* |
768 | * There could be 'spurious' loops in the lock graph due to ww_mutex, | |
769 | * consider: | |
770 | * | |
771 | * P1: A, ww_A, ww_B | |
772 | * P2: ww_B, ww_A | |
773 | * P3: A | |
774 | * | |
775 | * P3 should not return -EDEADLK because it gets trapped in the cycle | |
776 | * created by P1 and P2 (which will resolve -- and runs into | |
777 | * max_lock_depth above). Therefore disable detect_deadlock such that | |
778 | * the below termination condition can trigger once all relevant tasks | |
779 | * are boosted. | |
780 | * | |
781 | * Even when we start with ww_mutex we can disable deadlock detection, | |
782 | * since we would supress a ww_mutex induced deadlock at [6] anyway. | |
783 | * Supressing it here however is not sufficient since we might still | |
784 | * hit [6] due to adjustment driven iteration. | |
785 | * | |
786 | * NOTE: if someone were to create a deadlock between 2 ww_classes we'd | |
787 | * utterly fail to report it; lockdep should. | |
788 | */ | |
789 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock) | |
790 | detect_deadlock = false; | |
791 | ||
1a539a87 TG |
792 | /* |
793 | * Drop out, when the task has no waiters. Note, | |
794 | * top_waiter can be NULL, when we are in the deboosting | |
795 | * mode! | |
796 | */ | |
397335f0 TG |
797 | if (top_waiter) { |
798 | if (!task_has_pi_waiters(task)) | |
799 | goto out_unlock_pi; | |
800 | /* | |
801 | * If deadlock detection is off, we stop here if we | |
67792e2c TG |
802 | * are not the top pi waiter of the task. If deadlock |
803 | * detection is enabled we continue, but stop the | |
804 | * requeueing in the chain walk. | |
397335f0 | 805 | */ |
67792e2c TG |
806 | if (top_waiter != task_top_pi_waiter(task)) { |
807 | if (!detect_deadlock) | |
808 | goto out_unlock_pi; | |
809 | else | |
810 | requeue = false; | |
811 | } | |
397335f0 | 812 | } |
23f78d4a IM |
813 | |
814 | /* | |
67792e2c TG |
815 | * If the waiter priority is the same as the task priority |
816 | * then there is no further priority adjustment necessary. If | |
817 | * deadlock detection is off, we stop the chain walk. If its | |
818 | * enabled we continue, but stop the requeueing in the chain | |
819 | * walk. | |
23f78d4a | 820 | */ |
f7853c34 | 821 | if (rt_waiter_node_equal(&waiter->tree, task_to_waiter_node(task))) { |
67792e2c TG |
822 | if (!detect_deadlock) |
823 | goto out_unlock_pi; | |
824 | else | |
825 | requeue = false; | |
826 | } | |
23f78d4a | 827 | |
3eb65aea | 828 | /* |
f7853c34 PZ |
829 | * [4] Get the next lock; per holding task->pi_lock we can't unblock |
830 | * and guarantee @lock's existence. | |
3eb65aea | 831 | */ |
23f78d4a | 832 | lock = waiter->lock; |
3eb65aea TG |
833 | /* |
834 | * [5] We need to trylock here as we are holding task->pi_lock, | |
835 | * which is the reverse lock order versus the other rtmutex | |
836 | * operations. | |
f7853c34 PZ |
837 | * |
838 | * Per the above, holding task->pi_lock guarantees lock exists, so | |
839 | * inverting this lock order is infeasible from a life-time | |
840 | * perspective. | |
3eb65aea | 841 | */ |
d209d74d | 842 | if (!raw_spin_trylock(&lock->wait_lock)) { |
b4abf910 | 843 | raw_spin_unlock_irq(&task->pi_lock); |
23f78d4a IM |
844 | cpu_relax(); |
845 | goto retry; | |
846 | } | |
847 | ||
397335f0 | 848 | /* |
3eb65aea TG |
849 | * [6] check_exit_conditions_2() protected by task->pi_lock and |
850 | * lock->wait_lock. | |
851 | * | |
397335f0 TG |
852 | * Deadlock detection. If the lock is the same as the original |
853 | * lock which caused us to walk the lock chain or if the | |
854 | * current lock is owned by the task which initiated the chain | |
855 | * walk, we detected a deadlock. | |
856 | */ | |
95e02ca9 | 857 | if (lock == orig_lock || rt_mutex_owner(lock) == top_task) { |
3d5c9340 | 858 | ret = -EDEADLK; |
a055fcc1 PZ |
859 | |
860 | /* | |
861 | * When the deadlock is due to ww_mutex; also see above. Don't | |
862 | * report the deadlock and instead let the ww_mutex wound/die | |
863 | * logic pick which of the contending threads gets -EDEADLK. | |
864 | * | |
865 | * NOTE: assumes the cycle only contains a single ww_class; any | |
866 | * other configuration and we fail to report; also, see | |
867 | * lockdep. | |
868 | */ | |
e5480572 | 869 | if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx) |
a055fcc1 PZ |
870 | ret = 0; |
871 | ||
872 | raw_spin_unlock(&lock->wait_lock); | |
23f78d4a IM |
873 | goto out_unlock_pi; |
874 | } | |
875 | ||
67792e2c TG |
876 | /* |
877 | * If we just follow the lock chain for deadlock detection, no | |
878 | * need to do all the requeue operations. To avoid a truckload | |
879 | * of conditionals around the various places below, just do the | |
880 | * minimum chain walk checks. | |
881 | */ | |
882 | if (!requeue) { | |
883 | /* | |
884 | * No requeue[7] here. Just release @task [8] | |
885 | */ | |
b4abf910 | 886 | raw_spin_unlock(&task->pi_lock); |
67792e2c TG |
887 | put_task_struct(task); |
888 | ||
889 | /* | |
890 | * [9] check_exit_conditions_3 protected by lock->wait_lock. | |
891 | * If there is no owner of the lock, end of chain. | |
892 | */ | |
893 | if (!rt_mutex_owner(lock)) { | |
b4abf910 | 894 | raw_spin_unlock_irq(&lock->wait_lock); |
67792e2c TG |
895 | return 0; |
896 | } | |
897 | ||
898 | /* [10] Grab the next task, i.e. owner of @lock */ | |
7b3c92b8 | 899 | task = get_task_struct(rt_mutex_owner(lock)); |
b4abf910 | 900 | raw_spin_lock(&task->pi_lock); |
67792e2c TG |
901 | |
902 | /* | |
903 | * No requeue [11] here. We just do deadlock detection. | |
904 | * | |
905 | * [12] Store whether owner is blocked | |
906 | * itself. Decision is made after dropping the locks | |
907 | */ | |
908 | next_lock = task_blocked_on_lock(task); | |
909 | /* | |
910 | * Get the top waiter for the next iteration | |
911 | */ | |
912 | top_waiter = rt_mutex_top_waiter(lock); | |
913 | ||
914 | /* [13] Drop locks */ | |
b4abf910 TG |
915 | raw_spin_unlock(&task->pi_lock); |
916 | raw_spin_unlock_irq(&lock->wait_lock); | |
67792e2c TG |
917 | |
918 | /* If owner is not blocked, end of chain. */ | |
919 | if (!next_lock) | |
920 | goto out_put_task; | |
921 | goto again; | |
922 | } | |
923 | ||
a57594a1 TG |
924 | /* |
925 | * Store the current top waiter before doing the requeue | |
926 | * operation on @lock. We need it for the boost/deboost | |
927 | * decision below. | |
928 | */ | |
929 | prerequeue_top_waiter = rt_mutex_top_waiter(lock); | |
23f78d4a | 930 | |
9f40a51a | 931 | /* [7] Requeue the waiter in the lock waiter tree. */ |
fb00aca4 | 932 | rt_mutex_dequeue(lock, waiter); |
e0aad5b4 PZ |
933 | |
934 | /* | |
935 | * Update the waiter prio fields now that we're dequeued. | |
936 | * | |
937 | * These values can have changed through either: | |
938 | * | |
939 | * sys_sched_set_scheduler() / sys_sched_setattr() | |
940 | * | |
941 | * or | |
942 | * | |
943 | * DL CBS enforcement advancing the effective deadline. | |
e0aad5b4 | 944 | */ |
715f7f9e | 945 | waiter_update_prio(waiter, task); |
e0aad5b4 | 946 | |
fb00aca4 | 947 | rt_mutex_enqueue(lock, waiter); |
23f78d4a | 948 | |
f7853c34 PZ |
949 | /* |
950 | * [8] Release the (blocking) task in preparation for | |
951 | * taking the owner task in [10]. | |
952 | * | |
953 | * Since we hold lock->waiter_lock, task cannot unblock, even if we | |
954 | * release task->pi_lock. | |
955 | */ | |
b4abf910 | 956 | raw_spin_unlock(&task->pi_lock); |
2ffa5a5c TG |
957 | put_task_struct(task); |
958 | ||
a57594a1 | 959 | /* |
3eb65aea TG |
960 | * [9] check_exit_conditions_3 protected by lock->wait_lock. |
961 | * | |
a57594a1 TG |
962 | * We must abort the chain walk if there is no lock owner even |
963 | * in the dead lock detection case, as we have nothing to | |
964 | * follow here. This is the end of the chain we are walking. | |
965 | */ | |
8161239a LJ |
966 | if (!rt_mutex_owner(lock)) { |
967 | /* | |
3eb65aea TG |
968 | * If the requeue [7] above changed the top waiter, |
969 | * then we need to wake the new top waiter up to try | |
970 | * to get the lock. | |
8161239a | 971 | */ |
db370a8b WLC |
972 | top_waiter = rt_mutex_top_waiter(lock); |
973 | if (prerequeue_top_waiter != top_waiter) | |
974 | wake_up_state(top_waiter->task, top_waiter->wake_state); | |
b4abf910 | 975 | raw_spin_unlock_irq(&lock->wait_lock); |
2ffa5a5c | 976 | return 0; |
8161239a | 977 | } |
23f78d4a | 978 | |
f7853c34 PZ |
979 | /* |
980 | * [10] Grab the next task, i.e. the owner of @lock | |
981 | * | |
982 | * Per holding lock->wait_lock and checking for !owner above, there | |
983 | * must be an owner and it cannot go away. | |
984 | */ | |
7b3c92b8 | 985 | task = get_task_struct(rt_mutex_owner(lock)); |
b4abf910 | 986 | raw_spin_lock(&task->pi_lock); |
23f78d4a | 987 | |
3eb65aea | 988 | /* [11] requeue the pi waiters if necessary */ |
23f78d4a | 989 | if (waiter == rt_mutex_top_waiter(lock)) { |
a57594a1 TG |
990 | /* |
991 | * The waiter became the new top (highest priority) | |
992 | * waiter on the lock. Replace the previous top waiter | |
9f40a51a | 993 | * in the owner tasks pi waiters tree with this waiter |
a57594a1 TG |
994 | * and adjust the priority of the owner. |
995 | */ | |
996 | rt_mutex_dequeue_pi(task, prerequeue_top_waiter); | |
f7853c34 | 997 | waiter_clone_prio(waiter, task); |
fb00aca4 | 998 | rt_mutex_enqueue_pi(task, waiter); |
f7853c34 | 999 | rt_mutex_adjust_prio(lock, task); |
23f78d4a | 1000 | |
a57594a1 TG |
1001 | } else if (prerequeue_top_waiter == waiter) { |
1002 | /* | |
1003 | * The waiter was the top waiter on the lock, but is | |
e2db7592 | 1004 | * no longer the top priority waiter. Replace waiter in |
9f40a51a | 1005 | * the owner tasks pi waiters tree with the new top |
a57594a1 TG |
1006 | * (highest priority) waiter and adjust the priority |
1007 | * of the owner. | |
1008 | * The new top waiter is stored in @waiter so that | |
1009 | * @waiter == @top_waiter evaluates to true below and | |
1010 | * we continue to deboost the rest of the chain. | |
1011 | */ | |
fb00aca4 | 1012 | rt_mutex_dequeue_pi(task, waiter); |
23f78d4a | 1013 | waiter = rt_mutex_top_waiter(lock); |
f7853c34 | 1014 | waiter_clone_prio(waiter, task); |
fb00aca4 | 1015 | rt_mutex_enqueue_pi(task, waiter); |
f7853c34 | 1016 | rt_mutex_adjust_prio(lock, task); |
a57594a1 TG |
1017 | } else { |
1018 | /* | |
1019 | * Nothing changed. No need to do any priority | |
1020 | * adjustment. | |
1021 | */ | |
23f78d4a IM |
1022 | } |
1023 | ||
82084984 | 1024 | /* |
3eb65aea TG |
1025 | * [12] check_exit_conditions_4() protected by task->pi_lock |
1026 | * and lock->wait_lock. The actual decisions are made after we | |
1027 | * dropped the locks. | |
1028 | * | |
82084984 TG |
1029 | * Check whether the task which owns the current lock is pi |
1030 | * blocked itself. If yes we store a pointer to the lock for | |
1031 | * the lock chain change detection above. After we dropped | |
1032 | * task->pi_lock next_lock cannot be dereferenced anymore. | |
1033 | */ | |
1034 | next_lock = task_blocked_on_lock(task); | |
a57594a1 TG |
1035 | /* |
1036 | * Store the top waiter of @lock for the end of chain walk | |
1037 | * decision below. | |
1038 | */ | |
23f78d4a | 1039 | top_waiter = rt_mutex_top_waiter(lock); |
3eb65aea TG |
1040 | |
1041 | /* [13] Drop the locks */ | |
b4abf910 TG |
1042 | raw_spin_unlock(&task->pi_lock); |
1043 | raw_spin_unlock_irq(&lock->wait_lock); | |
23f78d4a | 1044 | |
82084984 | 1045 | /* |
3eb65aea TG |
1046 | * Make the actual exit decisions [12], based on the stored |
1047 | * values. | |
1048 | * | |
82084984 TG |
1049 | * We reached the end of the lock chain. Stop right here. No |
1050 | * point to go back just to figure that out. | |
1051 | */ | |
1052 | if (!next_lock) | |
1053 | goto out_put_task; | |
1054 | ||
a57594a1 TG |
1055 | /* |
1056 | * If the current waiter is not the top waiter on the lock, | |
1057 | * then we can stop the chain walk here if we are not in full | |
1058 | * deadlock detection mode. | |
1059 | */ | |
23f78d4a IM |
1060 | if (!detect_deadlock && waiter != top_waiter) |
1061 | goto out_put_task; | |
1062 | ||
1063 | goto again; | |
1064 | ||
1065 | out_unlock_pi: | |
b4abf910 | 1066 | raw_spin_unlock_irq(&task->pi_lock); |
23f78d4a IM |
1067 | out_put_task: |
1068 | put_task_struct(task); | |
36c8b586 | 1069 | |
23f78d4a IM |
1070 | return ret; |
1071 | } | |
1072 | ||
23f78d4a IM |
1073 | /* |
1074 | * Try to take an rt-mutex | |
1075 | * | |
b4abf910 | 1076 | * Must be called with lock->wait_lock held and interrupts disabled |
8161239a | 1077 | * |
358c331f TG |
1078 | * @lock: The lock to be acquired. |
1079 | * @task: The task which wants to acquire the lock | |
9f40a51a | 1080 | * @waiter: The waiter that is queued to the lock's wait tree if the |
358c331f | 1081 | * callsite called task_blocked_on_lock(), otherwise NULL |
23f78d4a | 1082 | */ |
d7a2edb8 | 1083 | static int __sched |
830e6acc | 1084 | try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task, |
d7a2edb8 | 1085 | struct rt_mutex_waiter *waiter) |
23f78d4a | 1086 | { |
e0aad5b4 PZ |
1087 | lockdep_assert_held(&lock->wait_lock); |
1088 | ||
23f78d4a | 1089 | /* |
358c331f TG |
1090 | * Before testing whether we can acquire @lock, we set the |
1091 | * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all | |
1092 | * other tasks which try to modify @lock into the slow path | |
1093 | * and they serialize on @lock->wait_lock. | |
23f78d4a | 1094 | * |
358c331f TG |
1095 | * The RT_MUTEX_HAS_WAITERS bit can have a transitional state |
1096 | * as explained at the top of this file if and only if: | |
23f78d4a | 1097 | * |
358c331f TG |
1098 | * - There is a lock owner. The caller must fixup the |
1099 | * transient state if it does a trylock or leaves the lock | |
1100 | * function due to a signal or timeout. | |
1101 | * | |
1102 | * - @task acquires the lock and there are no other | |
1103 | * waiters. This is undone in rt_mutex_set_owner(@task) at | |
1104 | * the end of this function. | |
23f78d4a IM |
1105 | */ |
1106 | mark_rt_mutex_waiters(lock); | |
1107 | ||
358c331f TG |
1108 | /* |
1109 | * If @lock has an owner, give up. | |
1110 | */ | |
8161239a | 1111 | if (rt_mutex_owner(lock)) |
23f78d4a IM |
1112 | return 0; |
1113 | ||
8161239a | 1114 | /* |
358c331f | 1115 | * If @waiter != NULL, @task has already enqueued the waiter |
9f40a51a | 1116 | * into @lock waiter tree. If @waiter == NULL then this is a |
358c331f | 1117 | * trylock attempt. |
8161239a | 1118 | */ |
358c331f | 1119 | if (waiter) { |
48eb3f4f | 1120 | struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock); |
8161239a | 1121 | |
358c331f | 1122 | /* |
48eb3f4f GH |
1123 | * If waiter is the highest priority waiter of @lock, |
1124 | * or allowed to steal it, take it over. | |
358c331f | 1125 | */ |
48eb3f4f GH |
1126 | if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) { |
1127 | /* | |
1128 | * We can acquire the lock. Remove the waiter from the | |
1129 | * lock waiters tree. | |
1130 | */ | |
1131 | rt_mutex_dequeue(lock, waiter); | |
1132 | } else { | |
1133 | return 0; | |
1134 | } | |
358c331f | 1135 | } else { |
8161239a | 1136 | /* |
358c331f TG |
1137 | * If the lock has waiters already we check whether @task is |
1138 | * eligible to take over the lock. | |
1139 | * | |
1140 | * If there are no other waiters, @task can acquire | |
1141 | * the lock. @task->pi_blocked_on is NULL, so it does | |
1142 | * not need to be dequeued. | |
8161239a LJ |
1143 | */ |
1144 | if (rt_mutex_has_waiters(lock)) { | |
48eb3f4f GH |
1145 | /* Check whether the trylock can steal it. */ |
1146 | if (!rt_mutex_steal(task_to_waiter(task), | |
1147 | rt_mutex_top_waiter(lock))) | |
358c331f TG |
1148 | return 0; |
1149 | ||
1150 | /* | |
1151 | * The current top waiter stays enqueued. We | |
1152 | * don't have to change anything in the lock | |
1153 | * waiters order. | |
1154 | */ | |
1155 | } else { | |
1156 | /* | |
1157 | * No waiters. Take the lock without the | |
1158 | * pi_lock dance.@task->pi_blocked_on is NULL | |
1159 | * and we have no waiters to enqueue in @task | |
9f40a51a | 1160 | * pi waiters tree. |
358c331f TG |
1161 | */ |
1162 | goto takeit; | |
8161239a | 1163 | } |
8161239a LJ |
1164 | } |
1165 | ||
358c331f TG |
1166 | /* |
1167 | * Clear @task->pi_blocked_on. Requires protection by | |
1168 | * @task->pi_lock. Redundant operation for the @waiter == NULL | |
1169 | * case, but conditionals are more expensive than a redundant | |
1170 | * store. | |
1171 | */ | |
b4abf910 | 1172 | raw_spin_lock(&task->pi_lock); |
358c331f TG |
1173 | task->pi_blocked_on = NULL; |
1174 | /* | |
1175 | * Finish the lock acquisition. @task is the new owner. If | |
1176 | * other waiters exist we have to insert the highest priority | |
9f40a51a | 1177 | * waiter into @task->pi_waiters tree. |
358c331f TG |
1178 | */ |
1179 | if (rt_mutex_has_waiters(lock)) | |
1180 | rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock)); | |
b4abf910 | 1181 | raw_spin_unlock(&task->pi_lock); |
358c331f TG |
1182 | |
1183 | takeit: | |
358c331f TG |
1184 | /* |
1185 | * This either preserves the RT_MUTEX_HAS_WAITERS bit if there | |
1186 | * are still waiters or clears it. | |
1187 | */ | |
8161239a | 1188 | rt_mutex_set_owner(lock, task); |
23f78d4a | 1189 | |
23f78d4a IM |
1190 | return 1; |
1191 | } | |
1192 | ||
1193 | /* | |
1194 | * Task blocks on lock. | |
1195 | * | |
1196 | * Prepare waiter and propagate pi chain | |
1197 | * | |
b4abf910 | 1198 | * This must be called with lock->wait_lock held and interrupts disabled |
23f78d4a | 1199 | */ |
830e6acc | 1200 | static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock, |
d7a2edb8 TG |
1201 | struct rt_mutex_waiter *waiter, |
1202 | struct task_struct *task, | |
add46132 | 1203 | struct ww_acquire_ctx *ww_ctx, |
d7a2edb8 | 1204 | enum rtmutex_chainwalk chwalk) |
23f78d4a | 1205 | { |
36c8b586 | 1206 | struct task_struct *owner = rt_mutex_owner(lock); |
23f78d4a | 1207 | struct rt_mutex_waiter *top_waiter = waiter; |
830e6acc | 1208 | struct rt_mutex_base *next_lock; |
db630637 | 1209 | int chain_walk = 0, res; |
23f78d4a | 1210 | |
e0aad5b4 PZ |
1211 | lockdep_assert_held(&lock->wait_lock); |
1212 | ||
397335f0 TG |
1213 | /* |
1214 | * Early deadlock detection. We really don't want the task to | |
1215 | * enqueue on itself just to untangle the mess later. It's not | |
1216 | * only an optimization. We drop the locks, so another waiter | |
1217 | * can come in before the chain walk detects the deadlock. So | |
1218 | * the other will detect the deadlock and return -EDEADLOCK, | |
1219 | * which is wrong, as the other waiter is not in a deadlock | |
1220 | * situation. | |
02ea9fc9 PZ |
1221 | * |
1222 | * Except for ww_mutex, in that case the chain walk must already deal | |
1223 | * with spurious cycles, see the comments at [3] and [6]. | |
397335f0 | 1224 | */ |
02ea9fc9 | 1225 | if (owner == task && !(build_ww_mutex() && ww_ctx)) |
397335f0 TG |
1226 | return -EDEADLK; |
1227 | ||
b4abf910 | 1228 | raw_spin_lock(&task->pi_lock); |
8dac456a | 1229 | waiter->task = task; |
23f78d4a | 1230 | waiter->lock = lock; |
715f7f9e | 1231 | waiter_update_prio(waiter, task); |
f7853c34 | 1232 | waiter_clone_prio(waiter, task); |
23f78d4a IM |
1233 | |
1234 | /* Get the top priority waiter on the lock */ | |
1235 | if (rt_mutex_has_waiters(lock)) | |
1236 | top_waiter = rt_mutex_top_waiter(lock); | |
fb00aca4 | 1237 | rt_mutex_enqueue(lock, waiter); |
23f78d4a | 1238 | |
8dac456a | 1239 | task->pi_blocked_on = waiter; |
23f78d4a | 1240 | |
b4abf910 | 1241 | raw_spin_unlock(&task->pi_lock); |
23f78d4a | 1242 | |
add46132 PZ |
1243 | if (build_ww_mutex() && ww_ctx) { |
1244 | struct rt_mutex *rtm; | |
1245 | ||
1246 | /* Check whether the waiter should back out immediately */ | |
1247 | rtm = container_of(lock, struct rt_mutex, rtmutex); | |
1248 | res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx); | |
37e8abff TG |
1249 | if (res) { |
1250 | raw_spin_lock(&task->pi_lock); | |
1251 | rt_mutex_dequeue(lock, waiter); | |
1252 | task->pi_blocked_on = NULL; | |
1253 | raw_spin_unlock(&task->pi_lock); | |
add46132 | 1254 | return res; |
37e8abff | 1255 | } |
add46132 PZ |
1256 | } |
1257 | ||
8161239a LJ |
1258 | if (!owner) |
1259 | return 0; | |
1260 | ||
b4abf910 | 1261 | raw_spin_lock(&owner->pi_lock); |
23f78d4a | 1262 | if (waiter == rt_mutex_top_waiter(lock)) { |
fb00aca4 PZ |
1263 | rt_mutex_dequeue_pi(owner, top_waiter); |
1264 | rt_mutex_enqueue_pi(owner, waiter); | |
23f78d4a | 1265 | |
f7853c34 | 1266 | rt_mutex_adjust_prio(lock, owner); |
db630637 SR |
1267 | if (owner->pi_blocked_on) |
1268 | chain_walk = 1; | |
8930ed80 | 1269 | } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) { |
db630637 | 1270 | chain_walk = 1; |
82084984 | 1271 | } |
db630637 | 1272 | |
82084984 TG |
1273 | /* Store the lock on which owner is blocked or NULL */ |
1274 | next_lock = task_blocked_on_lock(owner); | |
1275 | ||
b4abf910 | 1276 | raw_spin_unlock(&owner->pi_lock); |
82084984 TG |
1277 | /* |
1278 | * Even if full deadlock detection is on, if the owner is not | |
1279 | * blocked itself, we can avoid finding this out in the chain | |
1280 | * walk. | |
1281 | */ | |
1282 | if (!chain_walk || !next_lock) | |
23f78d4a IM |
1283 | return 0; |
1284 | ||
db630637 SR |
1285 | /* |
1286 | * The owner can't disappear while holding a lock, | |
1287 | * so the owner struct is protected by wait_lock. | |
1288 | * Gets dropped in rt_mutex_adjust_prio_chain()! | |
1289 | */ | |
1290 | get_task_struct(owner); | |
1291 | ||
b4abf910 | 1292 | raw_spin_unlock_irq(&lock->wait_lock); |
23f78d4a | 1293 | |
8930ed80 | 1294 | res = rt_mutex_adjust_prio_chain(owner, chwalk, lock, |
82084984 | 1295 | next_lock, waiter, task); |
23f78d4a | 1296 | |
b4abf910 | 1297 | raw_spin_lock_irq(&lock->wait_lock); |
23f78d4a IM |
1298 | |
1299 | return res; | |
1300 | } | |
1301 | ||
1302 | /* | |
9f40a51a | 1303 | * Remove the top waiter from the current tasks pi waiter tree and |
45ab4eff | 1304 | * queue it up. |
23f78d4a | 1305 | * |
b4abf910 | 1306 | * Called with lock->wait_lock held and interrupts disabled. |
23f78d4a | 1307 | */ |
7980aa39 | 1308 | static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh, |
830e6acc | 1309 | struct rt_mutex_base *lock) |
23f78d4a IM |
1310 | { |
1311 | struct rt_mutex_waiter *waiter; | |
23f78d4a | 1312 | |
f7853c34 PZ |
1313 | lockdep_assert_held(&lock->wait_lock); |
1314 | ||
b4abf910 | 1315 | raw_spin_lock(¤t->pi_lock); |
23f78d4a IM |
1316 | |
1317 | waiter = rt_mutex_top_waiter(lock); | |
23f78d4a IM |
1318 | |
1319 | /* | |
acd58620 PZ |
1320 | * Remove it from current->pi_waiters and deboost. |
1321 | * | |
1322 | * We must in fact deboost here in order to ensure we call | |
1323 | * rt_mutex_setprio() to update p->pi_top_task before the | |
1324 | * task unblocks. | |
23f78d4a | 1325 | */ |
fb00aca4 | 1326 | rt_mutex_dequeue_pi(current, waiter); |
f7853c34 | 1327 | rt_mutex_adjust_prio(lock, current); |
23f78d4a | 1328 | |
27e35715 TG |
1329 | /* |
1330 | * As we are waking up the top waiter, and the waiter stays | |
1331 | * queued on the lock until it gets the lock, this lock | |
1332 | * obviously has waiters. Just set the bit here and this has | |
1333 | * the added benefit of forcing all new tasks into the | |
1334 | * slow path making sure no task of lower priority than | |
1335 | * the top waiter can steal this lock. | |
1336 | */ | |
1337 | lock->owner = (void *) RT_MUTEX_HAS_WAITERS; | |
23f78d4a | 1338 | |
acd58620 PZ |
1339 | /* |
1340 | * We deboosted before waking the top waiter task such that we don't | |
1341 | * run two tasks with the 'same' priority (and ensure the | |
1342 | * p->pi_top_task pointer points to a blocked task). This however can | |
1343 | * lead to priority inversion if we would get preempted after the | |
1344 | * deboost but before waking our donor task, hence the preempt_disable() | |
1345 | * before unlock. | |
1346 | * | |
7980aa39 | 1347 | * Pairs with preempt_enable() in rt_mutex_wake_up_q(); |
acd58620 PZ |
1348 | */ |
1349 | preempt_disable(); | |
7980aa39 | 1350 | rt_mutex_wake_q_add(wqh, waiter); |
acd58620 | 1351 | raw_spin_unlock(¤t->pi_lock); |
23f78d4a IM |
1352 | } |
1353 | ||
e17ba59b TG |
1354 | static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock) |
1355 | { | |
1356 | int ret = try_to_take_rt_mutex(lock, current, NULL); | |
1357 | ||
1358 | /* | |
1359 | * try_to_take_rt_mutex() sets the lock waiters bit | |
1360 | * unconditionally. Clean this up. | |
1361 | */ | |
1c0908d8 | 1362 | fixup_rt_mutex_waiters(lock, true); |
e17ba59b TG |
1363 | |
1364 | return ret; | |
1365 | } | |
1366 | ||
1367 | /* | |
1368 | * Slow path try-lock function: | |
1369 | */ | |
1370 | static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock) | |
1371 | { | |
1372 | unsigned long flags; | |
1373 | int ret; | |
1374 | ||
1375 | /* | |
1376 | * If the lock already has an owner we fail to get the lock. | |
1377 | * This can be done without taking the @lock->wait_lock as | |
1378 | * it is only being read, and this is a trylock anyway. | |
1379 | */ | |
1380 | if (rt_mutex_owner(lock)) | |
1381 | return 0; | |
1382 | ||
1383 | /* | |
1384 | * The mutex has currently no owner. Lock the wait lock and try to | |
1385 | * acquire the lock. We use irqsave here to support early boot calls. | |
1386 | */ | |
1387 | raw_spin_lock_irqsave(&lock->wait_lock, flags); | |
1388 | ||
1389 | ret = __rt_mutex_slowtrylock(lock); | |
1390 | ||
1391 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags); | |
1392 | ||
1393 | return ret; | |
1394 | } | |
1395 | ||
1396 | static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock) | |
1397 | { | |
1398 | if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) | |
1399 | return 1; | |
1400 | ||
1401 | return rt_mutex_slowtrylock(lock); | |
1402 | } | |
1403 | ||
1404 | /* | |
1405 | * Slow path to release a rt-mutex. | |
1406 | */ | |
1407 | static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock) | |
1408 | { | |
1409 | DEFINE_RT_WAKE_Q(wqh); | |
1410 | unsigned long flags; | |
1411 | ||
1412 | /* irqsave required to support early boot calls */ | |
1413 | raw_spin_lock_irqsave(&lock->wait_lock, flags); | |
1414 | ||
1415 | debug_rt_mutex_unlock(lock); | |
1416 | ||
1417 | /* | |
1418 | * We must be careful here if the fast path is enabled. If we | |
1419 | * have no waiters queued we cannot set owner to NULL here | |
1420 | * because of: | |
1421 | * | |
1422 | * foo->lock->owner = NULL; | |
1423 | * rtmutex_lock(foo->lock); <- fast path | |
1424 | * free = atomic_dec_and_test(foo->refcnt); | |
1425 | * rtmutex_unlock(foo->lock); <- fast path | |
1426 | * if (free) | |
1427 | * kfree(foo); | |
1428 | * raw_spin_unlock(foo->lock->wait_lock); | |
1429 | * | |
1430 | * So for the fastpath enabled kernel: | |
1431 | * | |
1432 | * Nothing can set the waiters bit as long as we hold | |
1433 | * lock->wait_lock. So we do the following sequence: | |
1434 | * | |
1435 | * owner = rt_mutex_owner(lock); | |
1436 | * clear_rt_mutex_waiters(lock); | |
1437 | * raw_spin_unlock(&lock->wait_lock); | |
1438 | * if (cmpxchg(&lock->owner, owner, 0) == owner) | |
1439 | * return; | |
1440 | * goto retry; | |
1441 | * | |
1442 | * The fastpath disabled variant is simple as all access to | |
1443 | * lock->owner is serialized by lock->wait_lock: | |
1444 | * | |
1445 | * lock->owner = NULL; | |
1446 | * raw_spin_unlock(&lock->wait_lock); | |
1447 | */ | |
1448 | while (!rt_mutex_has_waiters(lock)) { | |
1449 | /* Drops lock->wait_lock ! */ | |
1450 | if (unlock_rt_mutex_safe(lock, flags) == true) | |
1451 | return; | |
1452 | /* Relock the rtmutex and try again */ | |
1453 | raw_spin_lock_irqsave(&lock->wait_lock, flags); | |
1454 | } | |
1455 | ||
1456 | /* | |
1457 | * The wakeup next waiter path does not suffer from the above | |
1458 | * race. See the comments there. | |
1459 | * | |
1460 | * Queue the next waiter for wakeup once we release the wait_lock. | |
1461 | */ | |
1462 | mark_wakeup_next_waiter(&wqh, lock); | |
1463 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags); | |
1464 | ||
1465 | rt_mutex_wake_up_q(&wqh); | |
1466 | } | |
1467 | ||
1468 | static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock) | |
1469 | { | |
1470 | if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) | |
1471 | return; | |
1472 | ||
1473 | rt_mutex_slowunlock(lock); | |
1474 | } | |
1475 | ||
992caf7f SR |
1476 | #ifdef CONFIG_SMP |
1477 | static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, | |
1478 | struct rt_mutex_waiter *waiter, | |
1479 | struct task_struct *owner) | |
1480 | { | |
1481 | bool res = true; | |
1482 | ||
1483 | rcu_read_lock(); | |
1484 | for (;;) { | |
1485 | /* If owner changed, trylock again. */ | |
1486 | if (owner != rt_mutex_owner(lock)) | |
1487 | break; | |
1488 | /* | |
1489 | * Ensure that @owner is dereferenced after checking that | |
1490 | * the lock owner still matches @owner. If that fails, | |
1491 | * @owner might point to freed memory. If it still matches, | |
1492 | * the rcu_read_lock() ensures the memory stays valid. | |
1493 | */ | |
1494 | barrier(); | |
1495 | /* | |
1496 | * Stop spinning when: | |
1497 | * - the lock owner has been scheduled out | |
1498 | * - current is not longer the top waiter | |
1499 | * - current is requested to reschedule (redundant | |
1500 | * for CONFIG_PREEMPT_RCU=y) | |
1501 | * - the VCPU on which owner runs is preempted | |
1502 | */ | |
c0bed69d | 1503 | if (!owner_on_cpu(owner) || need_resched() || |
f16cc980 | 1504 | !rt_mutex_waiter_is_top_waiter(lock, waiter)) { |
992caf7f SR |
1505 | res = false; |
1506 | break; | |
1507 | } | |
1508 | cpu_relax(); | |
1509 | } | |
1510 | rcu_read_unlock(); | |
1511 | return res; | |
1512 | } | |
1513 | #else | |
1514 | static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock, | |
1515 | struct rt_mutex_waiter *waiter, | |
1516 | struct task_struct *owner) | |
1517 | { | |
1518 | return false; | |
1519 | } | |
1520 | #endif | |
1521 | ||
e17ba59b TG |
1522 | #ifdef RT_MUTEX_BUILD_MUTEX |
1523 | /* | |
1524 | * Functions required for: | |
1525 | * - rtmutex, futex on all kernels | |
1526 | * - mutex and rwsem substitutions on RT kernels | |
1527 | */ | |
1528 | ||
23f78d4a | 1529 | /* |
8161239a | 1530 | * Remove a waiter from a lock and give up |
23f78d4a | 1531 | * |
e17ba59b | 1532 | * Must be called with lock->wait_lock held and interrupts disabled. It must |
8161239a | 1533 | * have just failed to try_to_take_rt_mutex(). |
23f78d4a | 1534 | */ |
830e6acc | 1535 | static void __sched remove_waiter(struct rt_mutex_base *lock, |
d7a2edb8 | 1536 | struct rt_mutex_waiter *waiter) |
23f78d4a | 1537 | { |
1ca7b860 | 1538 | bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock)); |
36c8b586 | 1539 | struct task_struct *owner = rt_mutex_owner(lock); |
830e6acc | 1540 | struct rt_mutex_base *next_lock; |
23f78d4a | 1541 | |
e0aad5b4 PZ |
1542 | lockdep_assert_held(&lock->wait_lock); |
1543 | ||
b4abf910 | 1544 | raw_spin_lock(¤t->pi_lock); |
fb00aca4 | 1545 | rt_mutex_dequeue(lock, waiter); |
23f78d4a | 1546 | current->pi_blocked_on = NULL; |
b4abf910 | 1547 | raw_spin_unlock(¤t->pi_lock); |
23f78d4a | 1548 | |
1ca7b860 TG |
1549 | /* |
1550 | * Only update priority if the waiter was the highest priority | |
1551 | * waiter of the lock and there is an owner to update. | |
1552 | */ | |
1553 | if (!owner || !is_top_waiter) | |
8161239a LJ |
1554 | return; |
1555 | ||
b4abf910 | 1556 | raw_spin_lock(&owner->pi_lock); |
23f78d4a | 1557 | |
1ca7b860 | 1558 | rt_mutex_dequeue_pi(owner, waiter); |
23f78d4a | 1559 | |
1ca7b860 TG |
1560 | if (rt_mutex_has_waiters(lock)) |
1561 | rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock)); | |
23f78d4a | 1562 | |
f7853c34 | 1563 | rt_mutex_adjust_prio(lock, owner); |
23f78d4a | 1564 | |
1ca7b860 TG |
1565 | /* Store the lock on which owner is blocked or NULL */ |
1566 | next_lock = task_blocked_on_lock(owner); | |
db630637 | 1567 | |
b4abf910 | 1568 | raw_spin_unlock(&owner->pi_lock); |
23f78d4a | 1569 | |
1ca7b860 TG |
1570 | /* |
1571 | * Don't walk the chain, if the owner task is not blocked | |
1572 | * itself. | |
1573 | */ | |
82084984 | 1574 | if (!next_lock) |
23f78d4a IM |
1575 | return; |
1576 | ||
db630637 SR |
1577 | /* gets dropped in rt_mutex_adjust_prio_chain()! */ |
1578 | get_task_struct(owner); | |
1579 | ||
b4abf910 | 1580 | raw_spin_unlock_irq(&lock->wait_lock); |
23f78d4a | 1581 | |
8930ed80 TG |
1582 | rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock, |
1583 | next_lock, NULL, current); | |
23f78d4a | 1584 | |
b4abf910 | 1585 | raw_spin_lock_irq(&lock->wait_lock); |
23f78d4a IM |
1586 | } |
1587 | ||
8dac456a | 1588 | /** |
ebbdc41e | 1589 | * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop |
8dac456a | 1590 | * @lock: the rt_mutex to take |
add46132 | 1591 | * @ww_ctx: WW mutex context pointer |
8dac456a | 1592 | * @state: the state the task should block in (TASK_INTERRUPTIBLE |
b4abf910 | 1593 | * or TASK_UNINTERRUPTIBLE) |
8dac456a DH |
1594 | * @timeout: the pre-initialized and started timer, or NULL for none |
1595 | * @waiter: the pre-initialized rt_mutex_waiter | |
8dac456a | 1596 | * |
b4abf910 | 1597 | * Must be called with lock->wait_lock held and interrupts disabled |
23f78d4a | 1598 | */ |
ebbdc41e | 1599 | static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock, |
add46132 | 1600 | struct ww_acquire_ctx *ww_ctx, |
ebbdc41e TG |
1601 | unsigned int state, |
1602 | struct hrtimer_sleeper *timeout, | |
1603 | struct rt_mutex_waiter *waiter) | |
23f78d4a | 1604 | { |
add46132 | 1605 | struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex); |
992caf7f | 1606 | struct task_struct *owner; |
23f78d4a IM |
1607 | int ret = 0; |
1608 | ||
23f78d4a IM |
1609 | for (;;) { |
1610 | /* Try to acquire the lock: */ | |
8161239a | 1611 | if (try_to_take_rt_mutex(lock, current, waiter)) |
23f78d4a IM |
1612 | break; |
1613 | ||
a51a327f TG |
1614 | if (timeout && !timeout->task) { |
1615 | ret = -ETIMEDOUT; | |
1616 | break; | |
1617 | } | |
1618 | if (signal_pending_state(state, current)) { | |
1619 | ret = -EINTR; | |
1620 | break; | |
23f78d4a IM |
1621 | } |
1622 | ||
add46132 PZ |
1623 | if (build_ww_mutex() && ww_ctx) { |
1624 | ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx); | |
1625 | if (ret) | |
1626 | break; | |
1627 | } | |
1628 | ||
992caf7f SR |
1629 | if (waiter == rt_mutex_top_waiter(lock)) |
1630 | owner = rt_mutex_owner(lock); | |
1631 | else | |
1632 | owner = NULL; | |
b4abf910 | 1633 | raw_spin_unlock_irq(&lock->wait_lock); |
23f78d4a | 1634 | |
992caf7f | 1635 | if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner)) |
d14f9e93 | 1636 | rt_mutex_schedule(); |
23f78d4a | 1637 | |
b4abf910 | 1638 | raw_spin_lock_irq(&lock->wait_lock); |
23f78d4a IM |
1639 | set_current_state(state); |
1640 | } | |
1641 | ||
afffc6c1 | 1642 | __set_current_state(TASK_RUNNING); |
8dac456a DH |
1643 | return ret; |
1644 | } | |
1645 | ||
d7a2edb8 TG |
1646 | static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock, |
1647 | struct rt_mutex_waiter *w) | |
3d5c9340 TG |
1648 | { |
1649 | /* | |
1650 | * If the result is not -EDEADLOCK or the caller requested | |
1651 | * deadlock detection, nothing to do here. | |
1652 | */ | |
1653 | if (res != -EDEADLOCK || detect_deadlock) | |
1654 | return; | |
1655 | ||
add46132 PZ |
1656 | if (build_ww_mutex() && w->ww_ctx) |
1657 | return; | |
1658 | ||
3d5c9340 | 1659 | /* |
e2db7592 | 1660 | * Yell loudly and stop the task right here. |
3d5c9340 | 1661 | */ |
6d41c675 | 1662 | WARN(1, "rtmutex deadlock detected\n"); |
3d5c9340 TG |
1663 | while (1) { |
1664 | set_current_state(TASK_INTERRUPTIBLE); | |
d14f9e93 | 1665 | rt_mutex_schedule(); |
3d5c9340 TG |
1666 | } |
1667 | } | |
1668 | ||
ebbdc41e TG |
1669 | /** |
1670 | * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held | |
1671 | * @lock: The rtmutex to block lock | |
add46132 | 1672 | * @ww_ctx: WW mutex context pointer |
ebbdc41e TG |
1673 | * @state: The task state for sleeping |
1674 | * @chwalk: Indicator whether full or partial chainwalk is requested | |
1675 | * @waiter: Initializer waiter for blocking | |
8dac456a | 1676 | */ |
ebbdc41e | 1677 | static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock, |
add46132 | 1678 | struct ww_acquire_ctx *ww_ctx, |
ebbdc41e TG |
1679 | unsigned int state, |
1680 | enum rtmutex_chainwalk chwalk, | |
1681 | struct rt_mutex_waiter *waiter) | |
8dac456a | 1682 | { |
add46132 PZ |
1683 | struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex); |
1684 | struct ww_mutex *ww = ww_container_of(rtm); | |
ebbdc41e | 1685 | int ret; |
8dac456a | 1686 | |
ebbdc41e | 1687 | lockdep_assert_held(&lock->wait_lock); |
8dac456a DH |
1688 | |
1689 | /* Try to acquire the lock again: */ | |
add46132 PZ |
1690 | if (try_to_take_rt_mutex(lock, current, NULL)) { |
1691 | if (build_ww_mutex() && ww_ctx) { | |
1692 | __ww_mutex_check_waiters(rtm, ww_ctx); | |
1693 | ww_mutex_lock_acquired(ww, ww_ctx); | |
1694 | } | |
8dac456a | 1695 | return 0; |
add46132 | 1696 | } |
8dac456a DH |
1697 | |
1698 | set_current_state(state); | |
1699 | ||
ee042be1 NK |
1700 | trace_contention_begin(lock, LCB_F_RT); |
1701 | ||
add46132 | 1702 | ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk); |
8161239a | 1703 | if (likely(!ret)) |
add46132 PZ |
1704 | ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter); |
1705 | ||
1706 | if (likely(!ret)) { | |
1707 | /* acquired the lock */ | |
1708 | if (build_ww_mutex() && ww_ctx) { | |
1709 | if (!ww_ctx->is_wait_die) | |
1710 | __ww_mutex_check_waiters(rtm, ww_ctx); | |
1711 | ww_mutex_lock_acquired(ww, ww_ctx); | |
1712 | } | |
1713 | } else { | |
9d3e2d02 | 1714 | __set_current_state(TASK_RUNNING); |
ebbdc41e TG |
1715 | remove_waiter(lock, waiter); |
1716 | rt_mutex_handle_deadlock(ret, chwalk, waiter); | |
3d5c9340 | 1717 | } |
23f78d4a IM |
1718 | |
1719 | /* | |
1720 | * try_to_take_rt_mutex() sets the waiter bit | |
1721 | * unconditionally. We might have to fix that up. | |
1722 | */ | |
1c0908d8 | 1723 | fixup_rt_mutex_waiters(lock, true); |
ee042be1 NK |
1724 | |
1725 | trace_contention_end(lock, ret); | |
1726 | ||
ebbdc41e TG |
1727 | return ret; |
1728 | } | |
23f78d4a | 1729 | |
ebbdc41e | 1730 | static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock, |
add46132 | 1731 | struct ww_acquire_ctx *ww_ctx, |
ebbdc41e TG |
1732 | unsigned int state) |
1733 | { | |
1734 | struct rt_mutex_waiter waiter; | |
1735 | int ret; | |
1736 | ||
1737 | rt_mutex_init_waiter(&waiter); | |
add46132 | 1738 | waiter.ww_ctx = ww_ctx; |
23f78d4a | 1739 | |
add46132 PZ |
1740 | ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK, |
1741 | &waiter); | |
23f78d4a | 1742 | |
23f78d4a | 1743 | debug_rt_mutex_free_waiter(&waiter); |
ebbdc41e TG |
1744 | return ret; |
1745 | } | |
1746 | ||
1747 | /* | |
1748 | * rt_mutex_slowlock - Locking slowpath invoked when fast path fails | |
1749 | * @lock: The rtmutex to block lock | |
add46132 | 1750 | * @ww_ctx: WW mutex context pointer |
ebbdc41e TG |
1751 | * @state: The task state for sleeping |
1752 | */ | |
1753 | static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock, | |
add46132 | 1754 | struct ww_acquire_ctx *ww_ctx, |
ebbdc41e TG |
1755 | unsigned int state) |
1756 | { | |
1757 | unsigned long flags; | |
1758 | int ret; | |
1759 | ||
d14f9e93 SAS |
1760 | /* |
1761 | * Do all pre-schedule work here, before we queue a waiter and invoke | |
1762 | * PI -- any such work that trips on rtlock (PREEMPT_RT spinlock) would | |
1763 | * otherwise recurse back into task_blocks_on_rt_mutex() through | |
1764 | * rtlock_slowlock() and will then enqueue a second waiter for this | |
1765 | * same task and things get really confusing real fast. | |
1766 | */ | |
1767 | rt_mutex_pre_schedule(); | |
1768 | ||
ebbdc41e TG |
1769 | /* |
1770 | * Technically we could use raw_spin_[un]lock_irq() here, but this can | |
1771 | * be called in early boot if the cmpxchg() fast path is disabled | |
1772 | * (debug, no architecture support). In this case we will acquire the | |
1773 | * rtmutex with lock->wait_lock held. But we cannot unconditionally | |
1774 | * enable interrupts in that early boot case. So we need to use the | |
1775 | * irqsave/restore variants. | |
1776 | */ | |
1777 | raw_spin_lock_irqsave(&lock->wait_lock, flags); | |
add46132 | 1778 | ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state); |
ebbdc41e | 1779 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags); |
d14f9e93 | 1780 | rt_mutex_post_schedule(); |
23f78d4a IM |
1781 | |
1782 | return ret; | |
1783 | } | |
1784 | ||
830e6acc | 1785 | static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock, |
531ae4b0 TG |
1786 | unsigned int state) |
1787 | { | |
45f67f30 TG |
1788 | lockdep_assert(!current->pi_blocked_on); |
1789 | ||
af9f0063 | 1790 | if (likely(rt_mutex_try_acquire(lock))) |
531ae4b0 TG |
1791 | return 0; |
1792 | ||
add46132 | 1793 | return rt_mutex_slowlock(lock, NULL, state); |
531ae4b0 | 1794 | } |
e17ba59b | 1795 | #endif /* RT_MUTEX_BUILD_MUTEX */ |
1c143c4b TG |
1796 | |
1797 | #ifdef RT_MUTEX_BUILD_SPINLOCKS | |
1798 | /* | |
1799 | * Functions required for spin/rw_lock substitution on RT kernels | |
1800 | */ | |
1801 | ||
1802 | /** | |
1803 | * rtlock_slowlock_locked - Slow path lock acquisition for RT locks | |
1804 | * @lock: The underlying RT mutex | |
1805 | */ | |
1806 | static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock) | |
1807 | { | |
1808 | struct rt_mutex_waiter waiter; | |
992caf7f | 1809 | struct task_struct *owner; |
1c143c4b TG |
1810 | |
1811 | lockdep_assert_held(&lock->wait_lock); | |
1812 | ||
1813 | if (try_to_take_rt_mutex(lock, current, NULL)) | |
1814 | return; | |
1815 | ||
1816 | rt_mutex_init_rtlock_waiter(&waiter); | |
1817 | ||
1818 | /* Save current state and set state to TASK_RTLOCK_WAIT */ | |
1819 | current_save_and_set_rtlock_wait_state(); | |
1820 | ||
ee042be1 NK |
1821 | trace_contention_begin(lock, LCB_F_RT); |
1822 | ||
add46132 | 1823 | task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK); |
1c143c4b TG |
1824 | |
1825 | for (;;) { | |
1826 | /* Try to acquire the lock again */ | |
1827 | if (try_to_take_rt_mutex(lock, current, &waiter)) | |
1828 | break; | |
1829 | ||
992caf7f SR |
1830 | if (&waiter == rt_mutex_top_waiter(lock)) |
1831 | owner = rt_mutex_owner(lock); | |
1832 | else | |
1833 | owner = NULL; | |
1c143c4b TG |
1834 | raw_spin_unlock_irq(&lock->wait_lock); |
1835 | ||
992caf7f SR |
1836 | if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner)) |
1837 | schedule_rtlock(); | |
1c143c4b TG |
1838 | |
1839 | raw_spin_lock_irq(&lock->wait_lock); | |
1840 | set_current_state(TASK_RTLOCK_WAIT); | |
1841 | } | |
1842 | ||
1843 | /* Restore the task state */ | |
1844 | current_restore_rtlock_saved_state(); | |
1845 | ||
1846 | /* | |
1847 | * try_to_take_rt_mutex() sets the waiter bit unconditionally. | |
1848 | * We might have to fix that up: | |
1849 | */ | |
1c0908d8 | 1850 | fixup_rt_mutex_waiters(lock, true); |
1c143c4b | 1851 | debug_rt_mutex_free_waiter(&waiter); |
ee042be1 NK |
1852 | |
1853 | trace_contention_end(lock, 0); | |
1c143c4b TG |
1854 | } |
1855 | ||
1856 | static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock) | |
1857 | { | |
1858 | unsigned long flags; | |
1859 | ||
1860 | raw_spin_lock_irqsave(&lock->wait_lock, flags); | |
1861 | rtlock_slowlock_locked(lock); | |
1862 | raw_spin_unlock_irqrestore(&lock->wait_lock, flags); | |
1863 | } | |
1864 | ||
1865 | #endif /* RT_MUTEX_BUILD_SPINLOCKS */ |