| 1 | /* |
| 2 | * RT-Mutexes: simple blocking mutual exclusion locks with PI support |
| 3 | * |
| 4 | * started by Ingo Molnar and Thomas Gleixner. |
| 5 | * |
| 6 | * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> |
| 7 | * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com> |
| 8 | * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt |
| 9 | * Copyright (C) 2006 Esben Nielsen |
| 10 | * |
| 11 | * See Documentation/rt-mutex-design.txt for details. |
| 12 | */ |
| 13 | #include <linux/spinlock.h> |
| 14 | #include <linux/export.h> |
| 15 | #include <linux/sched.h> |
| 16 | #include <linux/sched/rt.h> |
| 17 | #include <linux/timer.h> |
| 18 | |
| 19 | #include "rtmutex_common.h" |
| 20 | |
| 21 | /* |
| 22 | * lock->owner state tracking: |
| 23 | * |
| 24 | * lock->owner holds the task_struct pointer of the owner. Bit 0 |
| 25 | * is used to keep track of the "lock has waiters" state. |
| 26 | * |
| 27 | * owner bit0 |
| 28 | * NULL 0 lock is free (fast acquire possible) |
| 29 | * NULL 1 lock is free and has waiters and the top waiter |
| 30 | * is going to take the lock* |
| 31 | * taskpointer 0 lock is held (fast release possible) |
| 32 | * taskpointer 1 lock is held and has waiters** |
| 33 | * |
| 34 | * The fast atomic compare exchange based acquire and release is only |
| 35 | * possible when bit 0 of lock->owner is 0. |
| 36 | * |
| 37 | * (*) It also can be a transitional state when grabbing the lock |
| 38 | * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock, |
| 39 | * we need to set the bit0 before looking at the lock, and the owner may be |
| 40 | * NULL in this small time, hence this can be a transitional state. |
| 41 | * |
| 42 | * (**) There is a small time when bit 0 is set but there are no |
| 43 | * waiters. This can happen when grabbing the lock in the slow path. |
| 44 | * To prevent a cmpxchg of the owner releasing the lock, we need to |
| 45 | * set this bit before looking at the lock. |
| 46 | */ |
| 47 | |
| 48 | static void |
| 49 | rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner) |
| 50 | { |
| 51 | unsigned long val = (unsigned long)owner; |
| 52 | |
| 53 | if (rt_mutex_has_waiters(lock)) |
| 54 | val |= RT_MUTEX_HAS_WAITERS; |
| 55 | |
| 56 | lock->owner = (struct task_struct *)val; |
| 57 | } |
| 58 | |
| 59 | static inline void clear_rt_mutex_waiters(struct rt_mutex *lock) |
| 60 | { |
| 61 | lock->owner = (struct task_struct *) |
| 62 | ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS); |
| 63 | } |
| 64 | |
| 65 | static void fixup_rt_mutex_waiters(struct rt_mutex *lock) |
| 66 | { |
| 67 | unsigned long owner, *p = (unsigned long *) &lock->owner; |
| 68 | |
| 69 | if (rt_mutex_has_waiters(lock)) |
| 70 | return; |
| 71 | |
| 72 | /* |
| 73 | * The rbtree has no waiters enqueued, now make sure that the |
| 74 | * lock->owner still has the waiters bit set, otherwise the |
| 75 | * following can happen: |
| 76 | * |
| 77 | * CPU 0 CPU 1 CPU2 |
| 78 | * l->owner=T1 |
| 79 | * rt_mutex_lock(l) |
| 80 | * lock(l->lock) |
| 81 | * l->owner = T1 | HAS_WAITERS; |
| 82 | * enqueue(T2) |
| 83 | * boost() |
| 84 | * unlock(l->lock) |
| 85 | * block() |
| 86 | * |
| 87 | * rt_mutex_lock(l) |
| 88 | * lock(l->lock) |
| 89 | * l->owner = T1 | HAS_WAITERS; |
| 90 | * enqueue(T3) |
| 91 | * boost() |
| 92 | * unlock(l->lock) |
| 93 | * block() |
| 94 | * signal(->T2) signal(->T3) |
| 95 | * lock(l->lock) |
| 96 | * dequeue(T2) |
| 97 | * deboost() |
| 98 | * unlock(l->lock) |
| 99 | * lock(l->lock) |
| 100 | * dequeue(T3) |
| 101 | * ==> wait list is empty |
| 102 | * deboost() |
| 103 | * unlock(l->lock) |
| 104 | * lock(l->lock) |
| 105 | * fixup_rt_mutex_waiters() |
| 106 | * if (wait_list_empty(l) { |
| 107 | * l->owner = owner |
| 108 | * owner = l->owner & ~HAS_WAITERS; |
| 109 | * ==> l->owner = T1 |
| 110 | * } |
| 111 | * lock(l->lock) |
| 112 | * rt_mutex_unlock(l) fixup_rt_mutex_waiters() |
| 113 | * if (wait_list_empty(l) { |
| 114 | * owner = l->owner & ~HAS_WAITERS; |
| 115 | * cmpxchg(l->owner, T1, NULL) |
| 116 | * ===> Success (l->owner = NULL) |
| 117 | * |
| 118 | * l->owner = owner |
| 119 | * ==> l->owner = T1 |
| 120 | * } |
| 121 | * |
| 122 | * With the check for the waiter bit in place T3 on CPU2 will not |
| 123 | * overwrite. All tasks fiddling with the waiters bit are |
| 124 | * serialized by l->lock, so nothing else can modify the waiters |
| 125 | * bit. If the bit is set then nothing can change l->owner either |
| 126 | * so the simple RMW is safe. The cmpxchg() will simply fail if it |
| 127 | * happens in the middle of the RMW because the waiters bit is |
| 128 | * still set. |
| 129 | */ |
| 130 | owner = ACCESS_ONCE(*p); |
| 131 | if (owner & RT_MUTEX_HAS_WAITERS) |
| 132 | ACCESS_ONCE(*p) = owner & ~RT_MUTEX_HAS_WAITERS; |
| 133 | } |
| 134 | |
| 135 | /* |
| 136 | * We can speed up the acquire/release, if the architecture |
| 137 | * supports cmpxchg and if there's no debugging state to be set up |
| 138 | */ |
| 139 | #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES) |
| 140 | # define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c) |
| 141 | static inline void mark_rt_mutex_waiters(struct rt_mutex *lock) |
| 142 | { |
| 143 | unsigned long owner, *p = (unsigned long *) &lock->owner; |
| 144 | |
| 145 | do { |
| 146 | owner = *p; |
| 147 | } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner); |
| 148 | } |
| 149 | |
| 150 | /* |
| 151 | * Safe fastpath aware unlock: |
| 152 | * 1) Clear the waiters bit |
| 153 | * 2) Drop lock->wait_lock |
| 154 | * 3) Try to unlock the lock with cmpxchg |
| 155 | */ |
| 156 | static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock) |
| 157 | __releases(lock->wait_lock) |
| 158 | { |
| 159 | struct task_struct *owner = rt_mutex_owner(lock); |
| 160 | |
| 161 | clear_rt_mutex_waiters(lock); |
| 162 | raw_spin_unlock(&lock->wait_lock); |
| 163 | /* |
| 164 | * If a new waiter comes in between the unlock and the cmpxchg |
| 165 | * we have two situations: |
| 166 | * |
| 167 | * unlock(wait_lock); |
| 168 | * lock(wait_lock); |
| 169 | * cmpxchg(p, owner, 0) == owner |
| 170 | * mark_rt_mutex_waiters(lock); |
| 171 | * acquire(lock); |
| 172 | * or: |
| 173 | * |
| 174 | * unlock(wait_lock); |
| 175 | * lock(wait_lock); |
| 176 | * mark_rt_mutex_waiters(lock); |
| 177 | * |
| 178 | * cmpxchg(p, owner, 0) != owner |
| 179 | * enqueue_waiter(); |
| 180 | * unlock(wait_lock); |
| 181 | * lock(wait_lock); |
| 182 | * wake waiter(); |
| 183 | * unlock(wait_lock); |
| 184 | * lock(wait_lock); |
| 185 | * acquire(lock); |
| 186 | */ |
| 187 | return rt_mutex_cmpxchg(lock, owner, NULL); |
| 188 | } |
| 189 | |
| 190 | #else |
| 191 | # define rt_mutex_cmpxchg(l,c,n) (0) |
| 192 | static inline void mark_rt_mutex_waiters(struct rt_mutex *lock) |
| 193 | { |
| 194 | lock->owner = (struct task_struct *) |
| 195 | ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS); |
| 196 | } |
| 197 | |
| 198 | /* |
| 199 | * Simple slow path only version: lock->owner is protected by lock->wait_lock. |
| 200 | */ |
| 201 | static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock) |
| 202 | __releases(lock->wait_lock) |
| 203 | { |
| 204 | lock->owner = NULL; |
| 205 | raw_spin_unlock(&lock->wait_lock); |
| 206 | return true; |
| 207 | } |
| 208 | #endif |
| 209 | |
| 210 | /* |
| 211 | * Calculate task priority from the waiter list priority |
| 212 | * |
| 213 | * Return task->normal_prio when the waiter list is empty or when |
| 214 | * the waiter is not allowed to do priority boosting |
| 215 | */ |
| 216 | int rt_mutex_getprio(struct task_struct *task) |
| 217 | { |
| 218 | if (likely(!task_has_pi_waiters(task))) |
| 219 | return task->normal_prio; |
| 220 | |
| 221 | return min(task_top_pi_waiter(task)->pi_list_entry.prio, |
| 222 | task->normal_prio); |
| 223 | } |
| 224 | |
| 225 | /* |
| 226 | * Adjust the priority of a task, after its pi_waiters got modified. |
| 227 | * |
| 228 | * This can be both boosting and unboosting. task->pi_lock must be held. |
| 229 | */ |
| 230 | static void __rt_mutex_adjust_prio(struct task_struct *task) |
| 231 | { |
| 232 | int prio = rt_mutex_getprio(task); |
| 233 | |
| 234 | if (task->prio != prio) |
| 235 | rt_mutex_setprio(task, prio); |
| 236 | } |
| 237 | |
| 238 | /* |
| 239 | * Adjust task priority (undo boosting). Called from the exit path of |
| 240 | * rt_mutex_slowunlock() and rt_mutex_slowlock(). |
| 241 | * |
| 242 | * (Note: We do this outside of the protection of lock->wait_lock to |
| 243 | * allow the lock to be taken while or before we readjust the priority |
| 244 | * of task. We do not use the spin_xx_mutex() variants here as we are |
| 245 | * outside of the debug path.) |
| 246 | */ |
| 247 | static void rt_mutex_adjust_prio(struct task_struct *task) |
| 248 | { |
| 249 | unsigned long flags; |
| 250 | |
| 251 | raw_spin_lock_irqsave(&task->pi_lock, flags); |
| 252 | __rt_mutex_adjust_prio(task); |
| 253 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 254 | } |
| 255 | |
| 256 | /* |
| 257 | * Max number of times we'll walk the boosting chain: |
| 258 | */ |
| 259 | int max_lock_depth = 1024; |
| 260 | |
| 261 | static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p) |
| 262 | { |
| 263 | return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL; |
| 264 | } |
| 265 | |
| 266 | /* |
| 267 | * Adjust the priority chain. Also used for deadlock detection. |
| 268 | * Decreases task's usage by one - may thus free the task. |
| 269 | * Returns 0 or -EDEADLK. |
| 270 | */ |
| 271 | static int rt_mutex_adjust_prio_chain(struct task_struct *task, |
| 272 | int deadlock_detect, |
| 273 | struct rt_mutex *orig_lock, |
| 274 | struct rt_mutex *next_lock, |
| 275 | struct rt_mutex_waiter *orig_waiter, |
| 276 | struct task_struct *top_task) |
| 277 | { |
| 278 | struct rt_mutex *lock; |
| 279 | struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter; |
| 280 | int detect_deadlock, ret = 0, depth = 0; |
| 281 | unsigned long flags; |
| 282 | |
| 283 | detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter, |
| 284 | deadlock_detect); |
| 285 | |
| 286 | /* |
| 287 | * The (de)boosting is a step by step approach with a lot of |
| 288 | * pitfalls. We want this to be preemptible and we want hold a |
| 289 | * maximum of two locks per step. So we have to check |
| 290 | * carefully whether things change under us. |
| 291 | */ |
| 292 | again: |
| 293 | if (++depth > max_lock_depth) { |
| 294 | static int prev_max; |
| 295 | |
| 296 | /* |
| 297 | * Print this only once. If the admin changes the limit, |
| 298 | * print a new message when reaching the limit again. |
| 299 | */ |
| 300 | if (prev_max != max_lock_depth) { |
| 301 | prev_max = max_lock_depth; |
| 302 | printk(KERN_WARNING "Maximum lock depth %d reached " |
| 303 | "task: %s (%d)\n", max_lock_depth, |
| 304 | top_task->comm, task_pid_nr(top_task)); |
| 305 | } |
| 306 | put_task_struct(task); |
| 307 | |
| 308 | return -EDEADLK; |
| 309 | } |
| 310 | retry: |
| 311 | /* |
| 312 | * Task can not go away as we did a get_task() before ! |
| 313 | */ |
| 314 | raw_spin_lock_irqsave(&task->pi_lock, flags); |
| 315 | |
| 316 | waiter = task->pi_blocked_on; |
| 317 | /* |
| 318 | * Check whether the end of the boosting chain has been |
| 319 | * reached or the state of the chain has changed while we |
| 320 | * dropped the locks. |
| 321 | */ |
| 322 | if (!waiter) |
| 323 | goto out_unlock_pi; |
| 324 | |
| 325 | /* |
| 326 | * Check the orig_waiter state. After we dropped the locks, |
| 327 | * the previous owner of the lock might have released the lock. |
| 328 | */ |
| 329 | if (orig_waiter && !rt_mutex_owner(orig_lock)) |
| 330 | goto out_unlock_pi; |
| 331 | |
| 332 | /* |
| 333 | * We dropped all locks after taking a refcount on @task, so |
| 334 | * the task might have moved on in the lock chain or even left |
| 335 | * the chain completely and blocks now on an unrelated lock or |
| 336 | * on @orig_lock. |
| 337 | * |
| 338 | * We stored the lock on which @task was blocked in @next_lock, |
| 339 | * so we can detect the chain change. |
| 340 | */ |
| 341 | if (next_lock != waiter->lock) |
| 342 | goto out_unlock_pi; |
| 343 | |
| 344 | /* |
| 345 | * Drop out, when the task has no waiters. Note, |
| 346 | * top_waiter can be NULL, when we are in the deboosting |
| 347 | * mode! |
| 348 | */ |
| 349 | if (top_waiter) { |
| 350 | if (!task_has_pi_waiters(task)) |
| 351 | goto out_unlock_pi; |
| 352 | /* |
| 353 | * If deadlock detection is off, we stop here if we |
| 354 | * are not the top pi waiter of the task. |
| 355 | */ |
| 356 | if (!detect_deadlock && top_waiter != task_top_pi_waiter(task)) |
| 357 | goto out_unlock_pi; |
| 358 | } |
| 359 | |
| 360 | /* |
| 361 | * When deadlock detection is off then we check, if further |
| 362 | * priority adjustment is necessary. |
| 363 | */ |
| 364 | if (!detect_deadlock && waiter->list_entry.prio == task->prio) |
| 365 | goto out_unlock_pi; |
| 366 | |
| 367 | lock = waiter->lock; |
| 368 | if (!raw_spin_trylock(&lock->wait_lock)) { |
| 369 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 370 | cpu_relax(); |
| 371 | goto retry; |
| 372 | } |
| 373 | |
| 374 | /* |
| 375 | * Deadlock detection. If the lock is the same as the original |
| 376 | * lock which caused us to walk the lock chain or if the |
| 377 | * current lock is owned by the task which initiated the chain |
| 378 | * walk, we detected a deadlock. |
| 379 | */ |
| 380 | if (lock == orig_lock || rt_mutex_owner(lock) == top_task) { |
| 381 | debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock); |
| 382 | raw_spin_unlock(&lock->wait_lock); |
| 383 | ret = -EDEADLK; |
| 384 | goto out_unlock_pi; |
| 385 | } |
| 386 | |
| 387 | top_waiter = rt_mutex_top_waiter(lock); |
| 388 | |
| 389 | /* Requeue the waiter */ |
| 390 | plist_del(&waiter->list_entry, &lock->wait_list); |
| 391 | waiter->list_entry.prio = task->prio; |
| 392 | plist_add(&waiter->list_entry, &lock->wait_list); |
| 393 | |
| 394 | /* Release the task */ |
| 395 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 396 | if (!rt_mutex_owner(lock)) { |
| 397 | /* |
| 398 | * If the requeue above changed the top waiter, then we need |
| 399 | * to wake the new top waiter up to try to get the lock. |
| 400 | */ |
| 401 | |
| 402 | if (top_waiter != rt_mutex_top_waiter(lock)) |
| 403 | wake_up_process(rt_mutex_top_waiter(lock)->task); |
| 404 | raw_spin_unlock(&lock->wait_lock); |
| 405 | goto out_put_task; |
| 406 | } |
| 407 | put_task_struct(task); |
| 408 | |
| 409 | /* Grab the next task */ |
| 410 | task = rt_mutex_owner(lock); |
| 411 | get_task_struct(task); |
| 412 | raw_spin_lock_irqsave(&task->pi_lock, flags); |
| 413 | |
| 414 | if (waiter == rt_mutex_top_waiter(lock)) { |
| 415 | /* Boost the owner */ |
| 416 | plist_del(&top_waiter->pi_list_entry, &task->pi_waiters); |
| 417 | waiter->pi_list_entry.prio = waiter->list_entry.prio; |
| 418 | plist_add(&waiter->pi_list_entry, &task->pi_waiters); |
| 419 | __rt_mutex_adjust_prio(task); |
| 420 | |
| 421 | } else if (top_waiter == waiter) { |
| 422 | /* Deboost the owner */ |
| 423 | plist_del(&waiter->pi_list_entry, &task->pi_waiters); |
| 424 | waiter = rt_mutex_top_waiter(lock); |
| 425 | waiter->pi_list_entry.prio = waiter->list_entry.prio; |
| 426 | plist_add(&waiter->pi_list_entry, &task->pi_waiters); |
| 427 | __rt_mutex_adjust_prio(task); |
| 428 | } |
| 429 | |
| 430 | /* |
| 431 | * Check whether the task which owns the current lock is pi |
| 432 | * blocked itself. If yes we store a pointer to the lock for |
| 433 | * the lock chain change detection above. After we dropped |
| 434 | * task->pi_lock next_lock cannot be dereferenced anymore. |
| 435 | */ |
| 436 | next_lock = task_blocked_on_lock(task); |
| 437 | |
| 438 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 439 | |
| 440 | top_waiter = rt_mutex_top_waiter(lock); |
| 441 | raw_spin_unlock(&lock->wait_lock); |
| 442 | |
| 443 | /* |
| 444 | * We reached the end of the lock chain. Stop right here. No |
| 445 | * point to go back just to figure that out. |
| 446 | */ |
| 447 | if (!next_lock) |
| 448 | goto out_put_task; |
| 449 | |
| 450 | if (!detect_deadlock && waiter != top_waiter) |
| 451 | goto out_put_task; |
| 452 | |
| 453 | goto again; |
| 454 | |
| 455 | out_unlock_pi: |
| 456 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 457 | out_put_task: |
| 458 | put_task_struct(task); |
| 459 | |
| 460 | return ret; |
| 461 | } |
| 462 | |
| 463 | /* |
| 464 | * Try to take an rt-mutex |
| 465 | * |
| 466 | * Must be called with lock->wait_lock held. |
| 467 | * |
| 468 | * @lock: the lock to be acquired. |
| 469 | * @task: the task which wants to acquire the lock |
| 470 | * @waiter: the waiter that is queued to the lock's wait list. (could be NULL) |
| 471 | */ |
| 472 | static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task, |
| 473 | struct rt_mutex_waiter *waiter) |
| 474 | { |
| 475 | /* |
| 476 | * We have to be careful here if the atomic speedups are |
| 477 | * enabled, such that, when |
| 478 | * - no other waiter is on the lock |
| 479 | * - the lock has been released since we did the cmpxchg |
| 480 | * the lock can be released or taken while we are doing the |
| 481 | * checks and marking the lock with RT_MUTEX_HAS_WAITERS. |
| 482 | * |
| 483 | * The atomic acquire/release aware variant of |
| 484 | * mark_rt_mutex_waiters uses a cmpxchg loop. After setting |
| 485 | * the WAITERS bit, the atomic release / acquire can not |
| 486 | * happen anymore and lock->wait_lock protects us from the |
| 487 | * non-atomic case. |
| 488 | * |
| 489 | * Note, that this might set lock->owner = |
| 490 | * RT_MUTEX_HAS_WAITERS in the case the lock is not contended |
| 491 | * any more. This is fixed up when we take the ownership. |
| 492 | * This is the transitional state explained at the top of this file. |
| 493 | */ |
| 494 | mark_rt_mutex_waiters(lock); |
| 495 | |
| 496 | if (rt_mutex_owner(lock)) |
| 497 | return 0; |
| 498 | |
| 499 | /* |
| 500 | * It will get the lock because of one of these conditions: |
| 501 | * 1) there is no waiter |
| 502 | * 2) higher priority than waiters |
| 503 | * 3) it is top waiter |
| 504 | */ |
| 505 | if (rt_mutex_has_waiters(lock)) { |
| 506 | if (task->prio >= rt_mutex_top_waiter(lock)->list_entry.prio) { |
| 507 | if (!waiter || waiter != rt_mutex_top_waiter(lock)) |
| 508 | return 0; |
| 509 | } |
| 510 | } |
| 511 | |
| 512 | if (waiter || rt_mutex_has_waiters(lock)) { |
| 513 | unsigned long flags; |
| 514 | struct rt_mutex_waiter *top; |
| 515 | |
| 516 | raw_spin_lock_irqsave(&task->pi_lock, flags); |
| 517 | |
| 518 | /* remove the queued waiter. */ |
| 519 | if (waiter) { |
| 520 | plist_del(&waiter->list_entry, &lock->wait_list); |
| 521 | task->pi_blocked_on = NULL; |
| 522 | } |
| 523 | |
| 524 | /* |
| 525 | * We have to enqueue the top waiter(if it exists) into |
| 526 | * task->pi_waiters list. |
| 527 | */ |
| 528 | if (rt_mutex_has_waiters(lock)) { |
| 529 | top = rt_mutex_top_waiter(lock); |
| 530 | top->pi_list_entry.prio = top->list_entry.prio; |
| 531 | plist_add(&top->pi_list_entry, &task->pi_waiters); |
| 532 | } |
| 533 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 534 | } |
| 535 | |
| 536 | /* We got the lock. */ |
| 537 | debug_rt_mutex_lock(lock); |
| 538 | |
| 539 | rt_mutex_set_owner(lock, task); |
| 540 | |
| 541 | rt_mutex_deadlock_account_lock(lock, task); |
| 542 | |
| 543 | return 1; |
| 544 | } |
| 545 | |
| 546 | /* |
| 547 | * Task blocks on lock. |
| 548 | * |
| 549 | * Prepare waiter and propagate pi chain |
| 550 | * |
| 551 | * This must be called with lock->wait_lock held. |
| 552 | */ |
| 553 | static int task_blocks_on_rt_mutex(struct rt_mutex *lock, |
| 554 | struct rt_mutex_waiter *waiter, |
| 555 | struct task_struct *task, |
| 556 | int detect_deadlock) |
| 557 | { |
| 558 | struct task_struct *owner = rt_mutex_owner(lock); |
| 559 | struct rt_mutex_waiter *top_waiter = waiter; |
| 560 | struct rt_mutex *next_lock; |
| 561 | int chain_walk = 0, res; |
| 562 | unsigned long flags; |
| 563 | |
| 564 | /* |
| 565 | * Early deadlock detection. We really don't want the task to |
| 566 | * enqueue on itself just to untangle the mess later. It's not |
| 567 | * only an optimization. We drop the locks, so another waiter |
| 568 | * can come in before the chain walk detects the deadlock. So |
| 569 | * the other will detect the deadlock and return -EDEADLOCK, |
| 570 | * which is wrong, as the other waiter is not in a deadlock |
| 571 | * situation. |
| 572 | */ |
| 573 | if (owner == task) |
| 574 | return -EDEADLK; |
| 575 | |
| 576 | raw_spin_lock_irqsave(&task->pi_lock, flags); |
| 577 | __rt_mutex_adjust_prio(task); |
| 578 | waiter->task = task; |
| 579 | waiter->lock = lock; |
| 580 | plist_node_init(&waiter->list_entry, task->prio); |
| 581 | plist_node_init(&waiter->pi_list_entry, task->prio); |
| 582 | |
| 583 | /* Get the top priority waiter on the lock */ |
| 584 | if (rt_mutex_has_waiters(lock)) |
| 585 | top_waiter = rt_mutex_top_waiter(lock); |
| 586 | plist_add(&waiter->list_entry, &lock->wait_list); |
| 587 | |
| 588 | task->pi_blocked_on = waiter; |
| 589 | |
| 590 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 591 | |
| 592 | if (!owner) |
| 593 | return 0; |
| 594 | |
| 595 | raw_spin_lock_irqsave(&owner->pi_lock, flags); |
| 596 | if (waiter == rt_mutex_top_waiter(lock)) { |
| 597 | plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters); |
| 598 | plist_add(&waiter->pi_list_entry, &owner->pi_waiters); |
| 599 | |
| 600 | __rt_mutex_adjust_prio(owner); |
| 601 | if (owner->pi_blocked_on) |
| 602 | chain_walk = 1; |
| 603 | } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) { |
| 604 | chain_walk = 1; |
| 605 | } |
| 606 | |
| 607 | /* Store the lock on which owner is blocked or NULL */ |
| 608 | next_lock = task_blocked_on_lock(owner); |
| 609 | |
| 610 | raw_spin_unlock_irqrestore(&owner->pi_lock, flags); |
| 611 | /* |
| 612 | * Even if full deadlock detection is on, if the owner is not |
| 613 | * blocked itself, we can avoid finding this out in the chain |
| 614 | * walk. |
| 615 | */ |
| 616 | if (!chain_walk || !next_lock) |
| 617 | return 0; |
| 618 | |
| 619 | /* |
| 620 | * The owner can't disappear while holding a lock, |
| 621 | * so the owner struct is protected by wait_lock. |
| 622 | * Gets dropped in rt_mutex_adjust_prio_chain()! |
| 623 | */ |
| 624 | get_task_struct(owner); |
| 625 | |
| 626 | raw_spin_unlock(&lock->wait_lock); |
| 627 | |
| 628 | res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, |
| 629 | next_lock, waiter, task); |
| 630 | |
| 631 | raw_spin_lock(&lock->wait_lock); |
| 632 | |
| 633 | return res; |
| 634 | } |
| 635 | |
| 636 | /* |
| 637 | * Wake up the next waiter on the lock. |
| 638 | * |
| 639 | * Remove the top waiter from the current tasks pi waiter list and |
| 640 | * wake it up. |
| 641 | * |
| 642 | * Called with lock->wait_lock held. |
| 643 | */ |
| 644 | static void wakeup_next_waiter(struct rt_mutex *lock) |
| 645 | { |
| 646 | struct rt_mutex_waiter *waiter; |
| 647 | unsigned long flags; |
| 648 | |
| 649 | raw_spin_lock_irqsave(¤t->pi_lock, flags); |
| 650 | |
| 651 | waiter = rt_mutex_top_waiter(lock); |
| 652 | |
| 653 | /* |
| 654 | * Remove it from current->pi_waiters. We do not adjust a |
| 655 | * possible priority boost right now. We execute wakeup in the |
| 656 | * boosted mode and go back to normal after releasing |
| 657 | * lock->wait_lock. |
| 658 | */ |
| 659 | plist_del(&waiter->pi_list_entry, ¤t->pi_waiters); |
| 660 | |
| 661 | /* |
| 662 | * As we are waking up the top waiter, and the waiter stays |
| 663 | * queued on the lock until it gets the lock, this lock |
| 664 | * obviously has waiters. Just set the bit here and this has |
| 665 | * the added benefit of forcing all new tasks into the |
| 666 | * slow path making sure no task of lower priority than |
| 667 | * the top waiter can steal this lock. |
| 668 | */ |
| 669 | lock->owner = (void *) RT_MUTEX_HAS_WAITERS; |
| 670 | |
| 671 | raw_spin_unlock_irqrestore(¤t->pi_lock, flags); |
| 672 | |
| 673 | /* |
| 674 | * It's safe to dereference waiter as it cannot go away as |
| 675 | * long as we hold lock->wait_lock. The waiter task needs to |
| 676 | * acquire it in order to dequeue the waiter. |
| 677 | */ |
| 678 | wake_up_process(waiter->task); |
| 679 | } |
| 680 | |
| 681 | /* |
| 682 | * Remove a waiter from a lock and give up |
| 683 | * |
| 684 | * Must be called with lock->wait_lock held and |
| 685 | * have just failed to try_to_take_rt_mutex(). |
| 686 | */ |
| 687 | static void remove_waiter(struct rt_mutex *lock, |
| 688 | struct rt_mutex_waiter *waiter) |
| 689 | { |
| 690 | int first = (waiter == rt_mutex_top_waiter(lock)); |
| 691 | struct task_struct *owner = rt_mutex_owner(lock); |
| 692 | struct rt_mutex *next_lock = NULL; |
| 693 | unsigned long flags; |
| 694 | |
| 695 | raw_spin_lock_irqsave(¤t->pi_lock, flags); |
| 696 | plist_del(&waiter->list_entry, &lock->wait_list); |
| 697 | current->pi_blocked_on = NULL; |
| 698 | raw_spin_unlock_irqrestore(¤t->pi_lock, flags); |
| 699 | |
| 700 | if (!owner) |
| 701 | return; |
| 702 | |
| 703 | if (first) { |
| 704 | |
| 705 | raw_spin_lock_irqsave(&owner->pi_lock, flags); |
| 706 | |
| 707 | plist_del(&waiter->pi_list_entry, &owner->pi_waiters); |
| 708 | |
| 709 | if (rt_mutex_has_waiters(lock)) { |
| 710 | struct rt_mutex_waiter *next; |
| 711 | |
| 712 | next = rt_mutex_top_waiter(lock); |
| 713 | plist_add(&next->pi_list_entry, &owner->pi_waiters); |
| 714 | } |
| 715 | __rt_mutex_adjust_prio(owner); |
| 716 | |
| 717 | /* Store the lock on which owner is blocked or NULL */ |
| 718 | next_lock = task_blocked_on_lock(owner); |
| 719 | |
| 720 | raw_spin_unlock_irqrestore(&owner->pi_lock, flags); |
| 721 | } |
| 722 | |
| 723 | WARN_ON(!plist_node_empty(&waiter->pi_list_entry)); |
| 724 | |
| 725 | if (!next_lock) |
| 726 | return; |
| 727 | |
| 728 | /* gets dropped in rt_mutex_adjust_prio_chain()! */ |
| 729 | get_task_struct(owner); |
| 730 | |
| 731 | raw_spin_unlock(&lock->wait_lock); |
| 732 | |
| 733 | rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current); |
| 734 | |
| 735 | raw_spin_lock(&lock->wait_lock); |
| 736 | } |
| 737 | |
| 738 | /* |
| 739 | * Recheck the pi chain, in case we got a priority setting |
| 740 | * |
| 741 | * Called from sched_setscheduler |
| 742 | */ |
| 743 | void rt_mutex_adjust_pi(struct task_struct *task) |
| 744 | { |
| 745 | struct rt_mutex_waiter *waiter; |
| 746 | struct rt_mutex *next_lock; |
| 747 | unsigned long flags; |
| 748 | |
| 749 | raw_spin_lock_irqsave(&task->pi_lock, flags); |
| 750 | |
| 751 | waiter = task->pi_blocked_on; |
| 752 | if (!waiter || waiter->list_entry.prio == task->prio) { |
| 753 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 754 | return; |
| 755 | } |
| 756 | next_lock = waiter->lock; |
| 757 | raw_spin_unlock_irqrestore(&task->pi_lock, flags); |
| 758 | |
| 759 | /* gets dropped in rt_mutex_adjust_prio_chain()! */ |
| 760 | get_task_struct(task); |
| 761 | |
| 762 | rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task); |
| 763 | } |
| 764 | |
| 765 | /** |
| 766 | * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop |
| 767 | * @lock: the rt_mutex to take |
| 768 | * @state: the state the task should block in (TASK_INTERRUPTIBLE |
| 769 | * or TASK_UNINTERRUPTIBLE) |
| 770 | * @timeout: the pre-initialized and started timer, or NULL for none |
| 771 | * @waiter: the pre-initialized rt_mutex_waiter |
| 772 | * |
| 773 | * lock->wait_lock must be held by the caller. |
| 774 | */ |
| 775 | static int __sched |
| 776 | __rt_mutex_slowlock(struct rt_mutex *lock, int state, |
| 777 | struct hrtimer_sleeper *timeout, |
| 778 | struct rt_mutex_waiter *waiter) |
| 779 | { |
| 780 | int ret = 0; |
| 781 | |
| 782 | for (;;) { |
| 783 | /* Try to acquire the lock: */ |
| 784 | if (try_to_take_rt_mutex(lock, current, waiter)) |
| 785 | break; |
| 786 | |
| 787 | /* |
| 788 | * TASK_INTERRUPTIBLE checks for signals and |
| 789 | * timeout. Ignored otherwise. |
| 790 | */ |
| 791 | if (unlikely(state == TASK_INTERRUPTIBLE)) { |
| 792 | /* Signal pending? */ |
| 793 | if (signal_pending(current)) |
| 794 | ret = -EINTR; |
| 795 | if (timeout && !timeout->task) |
| 796 | ret = -ETIMEDOUT; |
| 797 | if (ret) |
| 798 | break; |
| 799 | } |
| 800 | |
| 801 | raw_spin_unlock(&lock->wait_lock); |
| 802 | |
| 803 | debug_rt_mutex_print_deadlock(waiter); |
| 804 | |
| 805 | schedule_rt_mutex(lock); |
| 806 | |
| 807 | raw_spin_lock(&lock->wait_lock); |
| 808 | set_current_state(state); |
| 809 | } |
| 810 | |
| 811 | return ret; |
| 812 | } |
| 813 | |
| 814 | static void rt_mutex_handle_deadlock(int res, int detect_deadlock, |
| 815 | struct rt_mutex_waiter *w) |
| 816 | { |
| 817 | /* |
| 818 | * If the result is not -EDEADLOCK or the caller requested |
| 819 | * deadlock detection, nothing to do here. |
| 820 | */ |
| 821 | if (res != -EDEADLOCK || detect_deadlock) |
| 822 | return; |
| 823 | |
| 824 | /* |
| 825 | * Yell lowdly and stop the task right here. |
| 826 | */ |
| 827 | rt_mutex_print_deadlock(w); |
| 828 | while (1) { |
| 829 | set_current_state(TASK_INTERRUPTIBLE); |
| 830 | schedule(); |
| 831 | } |
| 832 | } |
| 833 | |
| 834 | /* |
| 835 | * Slow path lock function: |
| 836 | */ |
| 837 | static int __sched |
| 838 | rt_mutex_slowlock(struct rt_mutex *lock, int state, |
| 839 | struct hrtimer_sleeper *timeout, |
| 840 | int detect_deadlock) |
| 841 | { |
| 842 | struct rt_mutex_waiter waiter; |
| 843 | int ret = 0; |
| 844 | |
| 845 | debug_rt_mutex_init_waiter(&waiter); |
| 846 | |
| 847 | raw_spin_lock(&lock->wait_lock); |
| 848 | |
| 849 | /* Try to acquire the lock again: */ |
| 850 | if (try_to_take_rt_mutex(lock, current, NULL)) { |
| 851 | raw_spin_unlock(&lock->wait_lock); |
| 852 | return 0; |
| 853 | } |
| 854 | |
| 855 | set_current_state(state); |
| 856 | |
| 857 | /* Setup the timer, when timeout != NULL */ |
| 858 | if (unlikely(timeout)) { |
| 859 | hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS); |
| 860 | if (!hrtimer_active(&timeout->timer)) |
| 861 | timeout->task = NULL; |
| 862 | } |
| 863 | |
| 864 | ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock); |
| 865 | |
| 866 | if (likely(!ret)) |
| 867 | ret = __rt_mutex_slowlock(lock, state, timeout, &waiter); |
| 868 | |
| 869 | set_current_state(TASK_RUNNING); |
| 870 | |
| 871 | if (unlikely(ret)) { |
| 872 | remove_waiter(lock, &waiter); |
| 873 | rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter); |
| 874 | } |
| 875 | |
| 876 | /* |
| 877 | * try_to_take_rt_mutex() sets the waiter bit |
| 878 | * unconditionally. We might have to fix that up. |
| 879 | */ |
| 880 | fixup_rt_mutex_waiters(lock); |
| 881 | |
| 882 | raw_spin_unlock(&lock->wait_lock); |
| 883 | |
| 884 | /* Remove pending timer: */ |
| 885 | if (unlikely(timeout)) |
| 886 | hrtimer_cancel(&timeout->timer); |
| 887 | |
| 888 | debug_rt_mutex_free_waiter(&waiter); |
| 889 | |
| 890 | return ret; |
| 891 | } |
| 892 | |
| 893 | /* |
| 894 | * Slow path try-lock function: |
| 895 | */ |
| 896 | static inline int |
| 897 | rt_mutex_slowtrylock(struct rt_mutex *lock) |
| 898 | { |
| 899 | int ret = 0; |
| 900 | |
| 901 | raw_spin_lock(&lock->wait_lock); |
| 902 | |
| 903 | if (likely(rt_mutex_owner(lock) != current)) { |
| 904 | |
| 905 | ret = try_to_take_rt_mutex(lock, current, NULL); |
| 906 | /* |
| 907 | * try_to_take_rt_mutex() sets the lock waiters |
| 908 | * bit unconditionally. Clean this up. |
| 909 | */ |
| 910 | fixup_rt_mutex_waiters(lock); |
| 911 | } |
| 912 | |
| 913 | raw_spin_unlock(&lock->wait_lock); |
| 914 | |
| 915 | return ret; |
| 916 | } |
| 917 | |
| 918 | /* |
| 919 | * Slow path to release a rt-mutex: |
| 920 | */ |
| 921 | static void __sched |
| 922 | rt_mutex_slowunlock(struct rt_mutex *lock) |
| 923 | { |
| 924 | raw_spin_lock(&lock->wait_lock); |
| 925 | |
| 926 | debug_rt_mutex_unlock(lock); |
| 927 | |
| 928 | rt_mutex_deadlock_account_unlock(current); |
| 929 | |
| 930 | /* |
| 931 | * We must be careful here if the fast path is enabled. If we |
| 932 | * have no waiters queued we cannot set owner to NULL here |
| 933 | * because of: |
| 934 | * |
| 935 | * foo->lock->owner = NULL; |
| 936 | * rtmutex_lock(foo->lock); <- fast path |
| 937 | * free = atomic_dec_and_test(foo->refcnt); |
| 938 | * rtmutex_unlock(foo->lock); <- fast path |
| 939 | * if (free) |
| 940 | * kfree(foo); |
| 941 | * raw_spin_unlock(foo->lock->wait_lock); |
| 942 | * |
| 943 | * So for the fastpath enabled kernel: |
| 944 | * |
| 945 | * Nothing can set the waiters bit as long as we hold |
| 946 | * lock->wait_lock. So we do the following sequence: |
| 947 | * |
| 948 | * owner = rt_mutex_owner(lock); |
| 949 | * clear_rt_mutex_waiters(lock); |
| 950 | * raw_spin_unlock(&lock->wait_lock); |
| 951 | * if (cmpxchg(&lock->owner, owner, 0) == owner) |
| 952 | * return; |
| 953 | * goto retry; |
| 954 | * |
| 955 | * The fastpath disabled variant is simple as all access to |
| 956 | * lock->owner is serialized by lock->wait_lock: |
| 957 | * |
| 958 | * lock->owner = NULL; |
| 959 | * raw_spin_unlock(&lock->wait_lock); |
| 960 | */ |
| 961 | while (!rt_mutex_has_waiters(lock)) { |
| 962 | /* Drops lock->wait_lock ! */ |
| 963 | if (unlock_rt_mutex_safe(lock) == true) |
| 964 | return; |
| 965 | /* Relock the rtmutex and try again */ |
| 966 | raw_spin_lock(&lock->wait_lock); |
| 967 | } |
| 968 | |
| 969 | /* |
| 970 | * The wakeup next waiter path does not suffer from the above |
| 971 | * race. See the comments there. |
| 972 | */ |
| 973 | wakeup_next_waiter(lock); |
| 974 | |
| 975 | raw_spin_unlock(&lock->wait_lock); |
| 976 | |
| 977 | /* Undo pi boosting if necessary: */ |
| 978 | rt_mutex_adjust_prio(current); |
| 979 | } |
| 980 | |
| 981 | /* |
| 982 | * debug aware fast / slowpath lock,trylock,unlock |
| 983 | * |
| 984 | * The atomic acquire/release ops are compiled away, when either the |
| 985 | * architecture does not support cmpxchg or when debugging is enabled. |
| 986 | */ |
| 987 | static inline int |
| 988 | rt_mutex_fastlock(struct rt_mutex *lock, int state, |
| 989 | int detect_deadlock, |
| 990 | int (*slowfn)(struct rt_mutex *lock, int state, |
| 991 | struct hrtimer_sleeper *timeout, |
| 992 | int detect_deadlock)) |
| 993 | { |
| 994 | if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) { |
| 995 | rt_mutex_deadlock_account_lock(lock, current); |
| 996 | return 0; |
| 997 | } else |
| 998 | return slowfn(lock, state, NULL, detect_deadlock); |
| 999 | } |
| 1000 | |
| 1001 | static inline int |
| 1002 | rt_mutex_timed_fastlock(struct rt_mutex *lock, int state, |
| 1003 | struct hrtimer_sleeper *timeout, int detect_deadlock, |
| 1004 | int (*slowfn)(struct rt_mutex *lock, int state, |
| 1005 | struct hrtimer_sleeper *timeout, |
| 1006 | int detect_deadlock)) |
| 1007 | { |
| 1008 | if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) { |
| 1009 | rt_mutex_deadlock_account_lock(lock, current); |
| 1010 | return 0; |
| 1011 | } else |
| 1012 | return slowfn(lock, state, timeout, detect_deadlock); |
| 1013 | } |
| 1014 | |
| 1015 | static inline int |
| 1016 | rt_mutex_fasttrylock(struct rt_mutex *lock, |
| 1017 | int (*slowfn)(struct rt_mutex *lock)) |
| 1018 | { |
| 1019 | if (likely(rt_mutex_cmpxchg(lock, NULL, current))) { |
| 1020 | rt_mutex_deadlock_account_lock(lock, current); |
| 1021 | return 1; |
| 1022 | } |
| 1023 | return slowfn(lock); |
| 1024 | } |
| 1025 | |
| 1026 | static inline void |
| 1027 | rt_mutex_fastunlock(struct rt_mutex *lock, |
| 1028 | void (*slowfn)(struct rt_mutex *lock)) |
| 1029 | { |
| 1030 | if (likely(rt_mutex_cmpxchg(lock, current, NULL))) |
| 1031 | rt_mutex_deadlock_account_unlock(current); |
| 1032 | else |
| 1033 | slowfn(lock); |
| 1034 | } |
| 1035 | |
| 1036 | /** |
| 1037 | * rt_mutex_lock - lock a rt_mutex |
| 1038 | * |
| 1039 | * @lock: the rt_mutex to be locked |
| 1040 | */ |
| 1041 | void __sched rt_mutex_lock(struct rt_mutex *lock) |
| 1042 | { |
| 1043 | might_sleep(); |
| 1044 | |
| 1045 | rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock); |
| 1046 | } |
| 1047 | EXPORT_SYMBOL_GPL(rt_mutex_lock); |
| 1048 | |
| 1049 | /** |
| 1050 | * rt_mutex_lock_interruptible - lock a rt_mutex interruptible |
| 1051 | * |
| 1052 | * @lock: the rt_mutex to be locked |
| 1053 | * @detect_deadlock: deadlock detection on/off |
| 1054 | * |
| 1055 | * Returns: |
| 1056 | * 0 on success |
| 1057 | * -EINTR when interrupted by a signal |
| 1058 | * -EDEADLK when the lock would deadlock (when deadlock detection is on) |
| 1059 | */ |
| 1060 | int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock, |
| 1061 | int detect_deadlock) |
| 1062 | { |
| 1063 | might_sleep(); |
| 1064 | |
| 1065 | return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, |
| 1066 | detect_deadlock, rt_mutex_slowlock); |
| 1067 | } |
| 1068 | EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible); |
| 1069 | |
| 1070 | /** |
| 1071 | * rt_mutex_timed_lock - lock a rt_mutex interruptible |
| 1072 | * the timeout structure is provided |
| 1073 | * by the caller |
| 1074 | * |
| 1075 | * @lock: the rt_mutex to be locked |
| 1076 | * @timeout: timeout structure or NULL (no timeout) |
| 1077 | * @detect_deadlock: deadlock detection on/off |
| 1078 | * |
| 1079 | * Returns: |
| 1080 | * 0 on success |
| 1081 | * -EINTR when interrupted by a signal |
| 1082 | * -ETIMEDOUT when the timeout expired |
| 1083 | * -EDEADLK when the lock would deadlock (when deadlock detection is on) |
| 1084 | */ |
| 1085 | int |
| 1086 | rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout, |
| 1087 | int detect_deadlock) |
| 1088 | { |
| 1089 | might_sleep(); |
| 1090 | |
| 1091 | return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout, |
| 1092 | detect_deadlock, rt_mutex_slowlock); |
| 1093 | } |
| 1094 | EXPORT_SYMBOL_GPL(rt_mutex_timed_lock); |
| 1095 | |
| 1096 | /** |
| 1097 | * rt_mutex_trylock - try to lock a rt_mutex |
| 1098 | * |
| 1099 | * @lock: the rt_mutex to be locked |
| 1100 | * |
| 1101 | * Returns 1 on success and 0 on contention |
| 1102 | */ |
| 1103 | int __sched rt_mutex_trylock(struct rt_mutex *lock) |
| 1104 | { |
| 1105 | return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock); |
| 1106 | } |
| 1107 | EXPORT_SYMBOL_GPL(rt_mutex_trylock); |
| 1108 | |
| 1109 | /** |
| 1110 | * rt_mutex_unlock - unlock a rt_mutex |
| 1111 | * |
| 1112 | * @lock: the rt_mutex to be unlocked |
| 1113 | */ |
| 1114 | void __sched rt_mutex_unlock(struct rt_mutex *lock) |
| 1115 | { |
| 1116 | rt_mutex_fastunlock(lock, rt_mutex_slowunlock); |
| 1117 | } |
| 1118 | EXPORT_SYMBOL_GPL(rt_mutex_unlock); |
| 1119 | |
| 1120 | /** |
| 1121 | * rt_mutex_destroy - mark a mutex unusable |
| 1122 | * @lock: the mutex to be destroyed |
| 1123 | * |
| 1124 | * This function marks the mutex uninitialized, and any subsequent |
| 1125 | * use of the mutex is forbidden. The mutex must not be locked when |
| 1126 | * this function is called. |
| 1127 | */ |
| 1128 | void rt_mutex_destroy(struct rt_mutex *lock) |
| 1129 | { |
| 1130 | WARN_ON(rt_mutex_is_locked(lock)); |
| 1131 | #ifdef CONFIG_DEBUG_RT_MUTEXES |
| 1132 | lock->magic = NULL; |
| 1133 | #endif |
| 1134 | } |
| 1135 | |
| 1136 | EXPORT_SYMBOL_GPL(rt_mutex_destroy); |
| 1137 | |
| 1138 | /** |
| 1139 | * __rt_mutex_init - initialize the rt lock |
| 1140 | * |
| 1141 | * @lock: the rt lock to be initialized |
| 1142 | * |
| 1143 | * Initialize the rt lock to unlocked state. |
| 1144 | * |
| 1145 | * Initializing of a locked rt lock is not allowed |
| 1146 | */ |
| 1147 | void __rt_mutex_init(struct rt_mutex *lock, const char *name) |
| 1148 | { |
| 1149 | lock->owner = NULL; |
| 1150 | raw_spin_lock_init(&lock->wait_lock); |
| 1151 | plist_head_init(&lock->wait_list); |
| 1152 | |
| 1153 | debug_rt_mutex_init(lock, name); |
| 1154 | } |
| 1155 | EXPORT_SYMBOL_GPL(__rt_mutex_init); |
| 1156 | |
| 1157 | /** |
| 1158 | * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a |
| 1159 | * proxy owner |
| 1160 | * |
| 1161 | * @lock: the rt_mutex to be locked |
| 1162 | * @proxy_owner:the task to set as owner |
| 1163 | * |
| 1164 | * No locking. Caller has to do serializing itself |
| 1165 | * Special API call for PI-futex support |
| 1166 | */ |
| 1167 | void rt_mutex_init_proxy_locked(struct rt_mutex *lock, |
| 1168 | struct task_struct *proxy_owner) |
| 1169 | { |
| 1170 | __rt_mutex_init(lock, NULL); |
| 1171 | debug_rt_mutex_proxy_lock(lock, proxy_owner); |
| 1172 | rt_mutex_set_owner(lock, proxy_owner); |
| 1173 | rt_mutex_deadlock_account_lock(lock, proxy_owner); |
| 1174 | } |
| 1175 | |
| 1176 | /** |
| 1177 | * rt_mutex_proxy_unlock - release a lock on behalf of owner |
| 1178 | * |
| 1179 | * @lock: the rt_mutex to be locked |
| 1180 | * |
| 1181 | * No locking. Caller has to do serializing itself |
| 1182 | * Special API call for PI-futex support |
| 1183 | */ |
| 1184 | void rt_mutex_proxy_unlock(struct rt_mutex *lock, |
| 1185 | struct task_struct *proxy_owner) |
| 1186 | { |
| 1187 | debug_rt_mutex_proxy_unlock(lock); |
| 1188 | rt_mutex_set_owner(lock, NULL); |
| 1189 | rt_mutex_deadlock_account_unlock(proxy_owner); |
| 1190 | } |
| 1191 | |
| 1192 | /** |
| 1193 | * rt_mutex_start_proxy_lock() - Start lock acquisition for another task |
| 1194 | * @lock: the rt_mutex to take |
| 1195 | * @waiter: the pre-initialized rt_mutex_waiter |
| 1196 | * @task: the task to prepare |
| 1197 | * @detect_deadlock: perform deadlock detection (1) or not (0) |
| 1198 | * |
| 1199 | * Returns: |
| 1200 | * 0 - task blocked on lock |
| 1201 | * 1 - acquired the lock for task, caller should wake it up |
| 1202 | * <0 - error |
| 1203 | * |
| 1204 | * Special API call for FUTEX_REQUEUE_PI support. |
| 1205 | */ |
| 1206 | int rt_mutex_start_proxy_lock(struct rt_mutex *lock, |
| 1207 | struct rt_mutex_waiter *waiter, |
| 1208 | struct task_struct *task, int detect_deadlock) |
| 1209 | { |
| 1210 | int ret; |
| 1211 | |
| 1212 | raw_spin_lock(&lock->wait_lock); |
| 1213 | |
| 1214 | if (try_to_take_rt_mutex(lock, task, NULL)) { |
| 1215 | raw_spin_unlock(&lock->wait_lock); |
| 1216 | return 1; |
| 1217 | } |
| 1218 | |
| 1219 | /* We enforce deadlock detection for futexes */ |
| 1220 | ret = task_blocks_on_rt_mutex(lock, waiter, task, 1); |
| 1221 | |
| 1222 | if (ret && !rt_mutex_owner(lock)) { |
| 1223 | /* |
| 1224 | * Reset the return value. We might have |
| 1225 | * returned with -EDEADLK and the owner |
| 1226 | * released the lock while we were walking the |
| 1227 | * pi chain. Let the waiter sort it out. |
| 1228 | */ |
| 1229 | ret = 0; |
| 1230 | } |
| 1231 | |
| 1232 | if (unlikely(ret)) |
| 1233 | remove_waiter(lock, waiter); |
| 1234 | |
| 1235 | raw_spin_unlock(&lock->wait_lock); |
| 1236 | |
| 1237 | debug_rt_mutex_print_deadlock(waiter); |
| 1238 | |
| 1239 | return ret; |
| 1240 | } |
| 1241 | |
| 1242 | /** |
| 1243 | * rt_mutex_next_owner - return the next owner of the lock |
| 1244 | * |
| 1245 | * @lock: the rt lock query |
| 1246 | * |
| 1247 | * Returns the next owner of the lock or NULL |
| 1248 | * |
| 1249 | * Caller has to serialize against other accessors to the lock |
| 1250 | * itself. |
| 1251 | * |
| 1252 | * Special API call for PI-futex support |
| 1253 | */ |
| 1254 | struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock) |
| 1255 | { |
| 1256 | if (!rt_mutex_has_waiters(lock)) |
| 1257 | return NULL; |
| 1258 | |
| 1259 | return rt_mutex_top_waiter(lock)->task; |
| 1260 | } |
| 1261 | |
| 1262 | /** |
| 1263 | * rt_mutex_finish_proxy_lock() - Complete lock acquisition |
| 1264 | * @lock: the rt_mutex we were woken on |
| 1265 | * @to: the timeout, null if none. hrtimer should already have |
| 1266 | * been started. |
| 1267 | * @waiter: the pre-initialized rt_mutex_waiter |
| 1268 | * @detect_deadlock: perform deadlock detection (1) or not (0) |
| 1269 | * |
| 1270 | * Complete the lock acquisition started our behalf by another thread. |
| 1271 | * |
| 1272 | * Returns: |
| 1273 | * 0 - success |
| 1274 | * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK |
| 1275 | * |
| 1276 | * Special API call for PI-futex requeue support |
| 1277 | */ |
| 1278 | int rt_mutex_finish_proxy_lock(struct rt_mutex *lock, |
| 1279 | struct hrtimer_sleeper *to, |
| 1280 | struct rt_mutex_waiter *waiter, |
| 1281 | int detect_deadlock) |
| 1282 | { |
| 1283 | int ret; |
| 1284 | |
| 1285 | raw_spin_lock(&lock->wait_lock); |
| 1286 | |
| 1287 | set_current_state(TASK_INTERRUPTIBLE); |
| 1288 | |
| 1289 | ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter); |
| 1290 | |
| 1291 | set_current_state(TASK_RUNNING); |
| 1292 | |
| 1293 | if (unlikely(ret)) |
| 1294 | remove_waiter(lock, waiter); |
| 1295 | |
| 1296 | /* |
| 1297 | * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might |
| 1298 | * have to fix that up. |
| 1299 | */ |
| 1300 | fixup_rt_mutex_waiters(lock); |
| 1301 | |
| 1302 | raw_spin_unlock(&lock->wait_lock); |
| 1303 | |
| 1304 | return ret; |
| 1305 | } |