kernel/locking/rtmutex.c

   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/locking/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/sched/deadline.h>
  18 #include <linux/timer.h>
  19
  20 #include "rtmutex_common.h"
  21
  22 /*
  23  * lock->owner state tracking:
  24  *
  25  * lock->owner holds the task_struct pointer of the owner. Bit 0
  26  * is used to keep track of the "lock has waiters" state.
  27  *
  28  * owner        bit0
  29  * NULL         0       lock is free (fast acquire possible)
  30  * NULL         1       lock is free and has waiters and the top waiter
  31  *                              is going to take the lock*
  32  * taskpointer  0       lock is held (fast release possible)
  33  * taskpointer  1       lock is held and has waiters**
  34  *
  35  * The fast atomic compare exchange based acquire and release is only
  36  * possible when bit 0 of lock->owner is 0.
  37  *
  38  * (*) It also can be a transitional state when grabbing the lock
  39  * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  40  * we need to set the bit0 before looking at the lock, and the owner may be
  41  * NULL in this small time, hence this can be a transitional state.
  42  *
  43  * (**) There is a small time when bit 0 is set but there are no
  44  * waiters. This can happen when grabbing the lock in the slow path.
  45  * To prevent a cmpxchg of the owner releasing the lock, we need to
  46  * set this bit before looking at the lock.
  47  */
  48
  49 static void
  50 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
  51 {
  52         unsigned long val = (unsigned long)owner;
  53
  54         if (rt_mutex_has_waiters(lock))
  55                 val |= RT_MUTEX_HAS_WAITERS;
  56
  57         lock->owner = (struct task_struct *)val;
  58 }
  59
  60 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  61 {
  62         lock->owner = (struct task_struct *)
  63                         ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  64 }
  65
  66 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  67 {
  68         if (!rt_mutex_has_waiters(lock))
  69                 clear_rt_mutex_waiters(lock);
  70 }
  71
  72 /*
  73  * We can speed up the acquire/release, if there's no debugging state to be
  74  * set up.
  75  */
  76 #ifndef CONFIG_DEBUG_RT_MUTEXES
  77 # define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
  78 # define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
  79 # define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
  80
  81 /*
  82  * Callers must hold the ->wait_lock -- which is the whole purpose as we force
  83  * all future threads that attempt to [Rmw] the lock to the slowpath. As such
  84  * relaxed semantics suffice.
  85  */
  86 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
  87 {
  88         unsigned long owner, *p = (unsigned long *) &lock->owner;
  89
  90         do {
  91                 owner = *p;
  92         } while (cmpxchg_relaxed(p, owner,
  93                                  owner | RT_MUTEX_HAS_WAITERS) != owner);
  94 }
  95
  96 /*
  97  * Safe fastpath aware unlock:
  98  * 1) Clear the waiters bit
  99  * 2) Drop lock->wait_lock
 100  * 3) Try to unlock the lock with cmpxchg
 101  */
 102 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
 103         __releases(lock->wait_lock)
 104 {
 105         struct task_struct *owner = rt_mutex_owner(lock);
 106
 107         clear_rt_mutex_waiters(lock);
 108         raw_spin_unlock(&lock->wait_lock);
 109         /*
 110          * If a new waiter comes in between the unlock and the cmpxchg
 111          * we have two situations:
 112          *
 113          * unlock(wait_lock);
 114          *                                      lock(wait_lock);
 115          * cmpxchg(p, owner, 0) == owner
 116          *                                      mark_rt_mutex_waiters(lock);
 117          *                                      acquire(lock);
 118          * or:
 119          *
 120          * unlock(wait_lock);
 121          *                                      lock(wait_lock);
 122          *                                      mark_rt_mutex_waiters(lock);
 123          *
 124          * cmpxchg(p, owner, 0) != owner
 125          *                                      enqueue_waiter();
 126          *                                      unlock(wait_lock);
 127          * lock(wait_lock);
 128          * wake waiter();
 129          * unlock(wait_lock);
 130          *                                      lock(wait_lock);
 131          *                                      acquire(lock);
 132          */
 133         return rt_mutex_cmpxchg_release(lock, owner, NULL);
 134 }
 135
 136 #else
 137 # define rt_mutex_cmpxchg_relaxed(l,c,n)        (0)
 138 # define rt_mutex_cmpxchg_acquire(l,c,n)        (0)
 139 # define rt_mutex_cmpxchg_release(l,c,n)        (0)
 140
 141 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 142 {
 143         lock->owner = (struct task_struct *)
 144                         ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 145 }
 146
 147 /*
 148  * Simple slow path only version: lock->owner is protected by lock->wait_lock.
 149  */
 150 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
 151         __releases(lock->wait_lock)
 152 {
 153         lock->owner = NULL;
 154         raw_spin_unlock(&lock->wait_lock);
 155         return true;
 156 }
 157 #endif
 158
 159 static inline int
 160 rt_mutex_waiter_less(struct rt_mutex_waiter *left,
 161                      struct rt_mutex_waiter *right)
 162 {
 163         if (left->prio < right->prio)
 164                 return 1;
 165
 166         /*
 167          * If both waiters have dl_prio(), we check the deadlines of the
 168          * associated tasks.
 169          * If left waiter has a dl_prio(), and we didn't return 1 above,
 170          * then right waiter has a dl_prio() too.
 171          */
 172         if (dl_prio(left->prio))
 173                 return (left->task->dl.deadline < right->task->dl.deadline);
 174
 175         return 0;
 176 }
 177
 178 static void
 179 rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 180 {
 181         struct rb_node **link = &lock->waiters.rb_node;
 182         struct rb_node *parent = NULL;
 183         struct rt_mutex_waiter *entry;
 184         int leftmost = 1;
 185
 186         while (*link) {
 187                 parent = *link;
 188                 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
 189                 if (rt_mutex_waiter_less(waiter, entry)) {
 190                         link = &parent->rb_left;
 191                 } else {
 192                         link = &parent->rb_right;
 193                         leftmost = 0;
 194                 }
 195         }
 196
 197         if (leftmost)
 198                 lock->waiters_leftmost = &waiter->tree_entry;
 199
 200         rb_link_node(&waiter->tree_entry, parent, link);
 201         rb_insert_color(&waiter->tree_entry, &lock->waiters);
 202 }
 203
 204 static void
 205 rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 206 {
 207         if (RB_EMPTY_NODE(&waiter->tree_entry))
 208                 return;
 209
 210         if (lock->waiters_leftmost == &waiter->tree_entry)
 211                 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
 212
 213         rb_erase(&waiter->tree_entry, &lock->waiters);
 214         RB_CLEAR_NODE(&waiter->tree_entry);
 215 }
 216
 217 static void
 218 rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 219 {
 220         struct rb_node **link = &task->pi_waiters.rb_node;
 221         struct rb_node *parent = NULL;
 222         struct rt_mutex_waiter *entry;
 223         int leftmost = 1;
 224
 225         while (*link) {
 226                 parent = *link;
 227                 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
 228                 if (rt_mutex_waiter_less(waiter, entry)) {
 229                         link = &parent->rb_left;
 230                 } else {
 231                         link = &parent->rb_right;
 232                         leftmost = 0;
 233                 }
 234         }
 235
 236         if (leftmost)
 237                 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
 238
 239         rb_link_node(&waiter->pi_tree_entry, parent, link);
 240         rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
 241 }
 242
 243 static void
 244 rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 245 {
 246         if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
 247                 return;
 248
 249         if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
 250                 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
 251
 252         rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
 253         RB_CLEAR_NODE(&waiter->pi_tree_entry);
 254 }
 255
 256 /*
 257  * Calculate task priority from the waiter tree priority
 258  *
 259  * Return task->normal_prio when the waiter tree is empty or when
 260  * the waiter is not allowed to do priority boosting
 261  */
 262 int rt_mutex_getprio(struct task_struct *task)
 263 {
 264         if (likely(!task_has_pi_waiters(task)))
 265                 return task->normal_prio;
 266
 267         return min(task_top_pi_waiter(task)->prio,
 268                    task->normal_prio);
 269 }
 270
 271 struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
 272 {
 273         if (likely(!task_has_pi_waiters(task)))
 274                 return NULL;
 275
 276         return task_top_pi_waiter(task)->task;
 277 }
 278
 279 /*
 280  * Called by sched_setscheduler() to get the priority which will be
 281  * effective after the change.
 282  */
 283 int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
 284 {
 285         if (!task_has_pi_waiters(task))
 286                 return newprio;
 287
 288         if (task_top_pi_waiter(task)->task->prio <= newprio)
 289                 return task_top_pi_waiter(task)->task->prio;
 290         return newprio;
 291 }
 292
 293 /*
 294  * Adjust the priority of a task, after its pi_waiters got modified.
 295  *
 296  * This can be both boosting and unboosting. task->pi_lock must be held.
 297  */
 298 static void __rt_mutex_adjust_prio(struct task_struct *task)
 299 {
 300         int prio = rt_mutex_getprio(task);
 301
 302         if (task->prio != prio || dl_prio(prio))
 303                 rt_mutex_setprio(task, prio);
 304 }
 305
 306 /*
 307  * Adjust task priority (undo boosting). Called from the exit path of
 308  * rt_mutex_slowunlock() and rt_mutex_slowlock().
 309  *
 310  * (Note: We do this outside of the protection of lock->wait_lock to
 311  * allow the lock to be taken while or before we readjust the priority
 312  * of task. We do not use the spin_xx_mutex() variants here as we are
 313  * outside of the debug path.)
 314  */
 315 void rt_mutex_adjust_prio(struct task_struct *task)
 316 {
 317         unsigned long flags;
 318
 319         raw_spin_lock_irqsave(&task->pi_lock, flags);
 320         __rt_mutex_adjust_prio(task);
 321         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 322 }
 323
 324 /*
 325  * Deadlock detection is conditional:
 326  *
 327  * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
 328  * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
 329  *
 330  * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
 331  * conducted independent of the detect argument.
 332  *
 333  * If the waiter argument is NULL this indicates the deboost path and
 334  * deadlock detection is disabled independent of the detect argument
 335  * and the config settings.
 336  */
 337 static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
 338                                           enum rtmutex_chainwalk chwalk)
 339 {
 340         /*
 341          * This is just a wrapper function for the following call,
 342          * because debug_rt_mutex_detect_deadlock() smells like a magic
 343          * debug feature and I wanted to keep the cond function in the
 344          * main source file along with the comments instead of having
 345          * two of the same in the headers.
 346          */
 347         return debug_rt_mutex_detect_deadlock(waiter, chwalk);
 348 }
 349
 350 /*
 351  * Max number of times we'll walk the boosting chain:
 352  */
 353 int max_lock_depth = 1024;
 354
 355 static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
 356 {
 357         return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 358 }
 359
 360 /*
 361  * Adjust the priority chain. Also used for deadlock detection.
 362  * Decreases task's usage by one - may thus free the task.
 363  *
 364  * @task:       the task owning the mutex (owner) for which a chain walk is
 365  *              probably needed
 366  * @chwalk:     do we have to carry out deadlock detection?
 367  * @orig_lock:  the mutex (can be NULL if we are walking the chain to recheck
 368  *              things for a task that has just got its priority adjusted, and
 369  *              is waiting on a mutex)
 370  * @next_lock:  the mutex on which the owner of @orig_lock was blocked before
 371  *              we dropped its pi_lock. Is never dereferenced, only used for
 372  *              comparison to detect lock chain changes.
 373  * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 374  *              its priority to the mutex owner (can be NULL in the case
 375  *              depicted above or if the top waiter is gone away and we are
 376  *              actually deboosting the owner)
 377  * @top_task:   the current top waiter
 378  *
 379  * Returns 0 or -EDEADLK.
 380  *
 381  * Chain walk basics and protection scope
 382  *
 383  * [R] refcount on task
 384  * [P] task->pi_lock held
 385  * [L] rtmutex->wait_lock held
 386  *
 387  * Step Description                             Protected by
 388  *      function arguments:
 389  *      @task                                   [R]
 390  *      @orig_lock if != NULL                   @top_task is blocked on it
 391  *      @next_lock                              Unprotected. Cannot be
 392  *                                              dereferenced. Only used for
 393  *                                              comparison.
 394  *      @orig_waiter if != NULL                 @top_task is blocked on it
 395  *      @top_task                               current, or in case of proxy
 396  *                                              locking protected by calling
 397  *                                              code
 398  *      again:
 399  *        loop_sanity_check();
 400  *      retry:
 401  * [1]    lock(task->pi_lock);                  [R] acquire [P]
 402  * [2]    waiter = task->pi_blocked_on;         [P]
 403  * [3]    check_exit_conditions_1();            [P]
 404  * [4]    lock = waiter->lock;                  [P]
 405  * [5]    if (!try_lock(lock->wait_lock)) {     [P] try to acquire [L]
 406  *          unlock(task->pi_lock);              release [P]
 407  *          goto retry;
 408  *        }
 409  * [6]    check_exit_conditions_2();            [P] + [L]
 410  * [7]    requeue_lock_waiter(lock, waiter);    [P] + [L]
 411  * [8]    unlock(task->pi_lock);                release [P]
 412  *        put_task_struct(task);                release [R]
 413  * [9]    check_exit_conditions_3();            [L]
 414  * [10]   task = owner(lock);                   [L]
 415  *        get_task_struct(task);                [L] acquire [R]
 416  *        lock(task->pi_lock);                  [L] acquire [P]
 417  * [11]   requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
 418  * [12]   check_exit_conditions_4();            [P] + [L]
 419  * [13]   unlock(task->pi_lock);                release [P]
 420  *        unlock(lock->wait_lock);              release [L]
 421  *        goto again;
 422  */
 423 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 424                                       enum rtmutex_chainwalk chwalk,
 425                                       struct rt_mutex *orig_lock,
 426                                       struct rt_mutex *next_lock,
 427                                       struct rt_mutex_waiter *orig_waiter,
 428                                       struct task_struct *top_task)
 429 {
 430         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 431         struct rt_mutex_waiter *prerequeue_top_waiter;
 432         int ret = 0, depth = 0;
 433         struct rt_mutex *lock;
 434         bool detect_deadlock;
 435         unsigned long flags;
 436         bool requeue = true;
 437
 438         detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
 439
 440         /*
 441          * The (de)boosting is a step by step approach with a lot of
 442          * pitfalls. We want this to be preemptible and we want hold a
 443          * maximum of two locks per step. So we have to check
 444          * carefully whether things change under us.
 445          */
 446  again:
 447         /*
 448          * We limit the lock chain length for each invocation.
 449          */
 450         if (++depth > max_lock_depth) {
 451                 static int prev_max;
 452
 453                 /*
 454                  * Print this only once. If the admin changes the limit,
 455                  * print a new message when reaching the limit again.
 456                  */
 457                 if (prev_max != max_lock_depth) {
 458                         prev_max = max_lock_depth;
 459                         printk(KERN_WARNING "Maximum lock depth %d reached "
 460                                "task: %s (%d)\n", max_lock_depth,
 461                                top_task->comm, task_pid_nr(top_task));
 462                 }
 463                 put_task_struct(task);
 464
 465                 return -EDEADLK;
 466         }
 467
 468         /*
 469          * We are fully preemptible here and only hold the refcount on
 470          * @task. So everything can have changed under us since the
 471          * caller or our own code below (goto retry/again) dropped all
 472          * locks.
 473          */
 474  retry:
 475         /*
 476          * [1] Task cannot go away as we did a get_task() before !
 477          */
 478         raw_spin_lock_irqsave(&task->pi_lock, flags);
 479
 480         /*
 481          * [2] Get the waiter on which @task is blocked on.
 482          */
 483         waiter = task->pi_blocked_on;
 484
 485         /*
 486          * [3] check_exit_conditions_1() protected by task->pi_lock.
 487          */
 488
 489         /*
 490          * Check whether the end of the boosting chain has been
 491          * reached or the state of the chain has changed while we
 492          * dropped the locks.
 493          */
 494         if (!waiter)
 495                 goto out_unlock_pi;
 496
 497         /*
 498          * Check the orig_waiter state. After we dropped the locks,
 499          * the previous owner of the lock might have released the lock.
 500          */
 501         if (orig_waiter && !rt_mutex_owner(orig_lock))
 502                 goto out_unlock_pi;
 503
 504         /*
 505          * We dropped all locks after taking a refcount on @task, so
 506          * the task might have moved on in the lock chain or even left
 507          * the chain completely and blocks now on an unrelated lock or
 508          * on @orig_lock.
 509          *
 510          * We stored the lock on which @task was blocked in @next_lock,
 511          * so we can detect the chain change.
 512          */
 513         if (next_lock != waiter->lock)
 514                 goto out_unlock_pi;
 515
 516         /*
 517          * Drop out, when the task has no waiters. Note,
 518          * top_waiter can be NULL, when we are in the deboosting
 519          * mode!
 520          */
 521         if (top_waiter) {
 522                 if (!task_has_pi_waiters(task))
 523                         goto out_unlock_pi;
 524                 /*
 525                  * If deadlock detection is off, we stop here if we
 526                  * are not the top pi waiter of the task. If deadlock
 527                  * detection is enabled we continue, but stop the
 528                  * requeueing in the chain walk.
 529                  */
 530                 if (top_waiter != task_top_pi_waiter(task)) {
 531                         if (!detect_deadlock)
 532                                 goto out_unlock_pi;
 533                         else
 534                                 requeue = false;
 535                 }
 536         }
 537
 538         /*
 539          * If the waiter priority is the same as the task priority
 540          * then there is no further priority adjustment necessary.  If
 541          * deadlock detection is off, we stop the chain walk. If its
 542          * enabled we continue, but stop the requeueing in the chain
 543          * walk.
 544          */
 545         if (waiter->prio == task->prio) {
 546                 if (!detect_deadlock)
 547                         goto out_unlock_pi;
 548                 else
 549                         requeue = false;
 550         }
 551
 552         /*
 553          * [4] Get the next lock
 554          */
 555         lock = waiter->lock;
 556         /*
 557          * [5] We need to trylock here as we are holding task->pi_lock,
 558          * which is the reverse lock order versus the other rtmutex
 559          * operations.
 560          */
 561         if (!raw_spin_trylock(&lock->wait_lock)) {
 562                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 563                 cpu_relax();
 564                 goto retry;
 565         }
 566
 567         /*
 568          * [6] check_exit_conditions_2() protected by task->pi_lock and
 569          * lock->wait_lock.
 570          *
 571          * Deadlock detection. If the lock is the same as the original
 572          * lock which caused us to walk the lock chain or if the
 573          * current lock is owned by the task which initiated the chain
 574          * walk, we detected a deadlock.
 575          */
 576         if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 577                 debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
 578                 raw_spin_unlock(&lock->wait_lock);
 579                 ret = -EDEADLK;
 580                 goto out_unlock_pi;
 581         }
 582
 583         /*
 584          * If we just follow the lock chain for deadlock detection, no
 585          * need to do all the requeue operations. To avoid a truckload
 586          * of conditionals around the various places below, just do the
 587          * minimum chain walk checks.
 588          */
 589         if (!requeue) {
 590                 /*
 591                  * No requeue[7] here. Just release @task [8]
 592                  */
 593                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 594                 put_task_struct(task);
 595
 596                 /*
 597                  * [9] check_exit_conditions_3 protected by lock->wait_lock.
 598                  * If there is no owner of the lock, end of chain.
 599                  */
 600                 if (!rt_mutex_owner(lock)) {
 601                         raw_spin_unlock(&lock->wait_lock);
 602                         return 0;
 603                 }
 604
 605                 /* [10] Grab the next task, i.e. owner of @lock */
 606                 task = rt_mutex_owner(lock);
 607                 get_task_struct(task);
 608                 raw_spin_lock_irqsave(&task->pi_lock, flags);
 609
 610                 /*
 611                  * No requeue [11] here. We just do deadlock detection.
 612                  *
 613                  * [12] Store whether owner is blocked
 614                  * itself. Decision is made after dropping the locks
 615                  */
 616                 next_lock = task_blocked_on_lock(task);
 617                 /*
 618                  * Get the top waiter for the next iteration
 619                  */
 620                 top_waiter = rt_mutex_top_waiter(lock);
 621
 622                 /* [13] Drop locks */
 623                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 624                 raw_spin_unlock(&lock->wait_lock);
 625
 626                 /* If owner is not blocked, end of chain. */
 627                 if (!next_lock)
 628                         goto out_put_task;
 629                 goto again;
 630         }
 631
 632         /*
 633          * Store the current top waiter before doing the requeue
 634          * operation on @lock. We need it for the boost/deboost
 635          * decision below.
 636          */
 637         prerequeue_top_waiter = rt_mutex_top_waiter(lock);
 638
 639         /* [7] Requeue the waiter in the lock waiter tree. */
 640         rt_mutex_dequeue(lock, waiter);
 641         waiter->prio = task->prio;
 642         rt_mutex_enqueue(lock, waiter);
 643
 644         /* [8] Release the task */
 645         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 646         put_task_struct(task);
 647
 648         /*
 649          * [9] check_exit_conditions_3 protected by lock->wait_lock.
 650          *
 651          * We must abort the chain walk if there is no lock owner even
 652          * in the dead lock detection case, as we have nothing to
 653          * follow here. This is the end of the chain we are walking.
 654          */
 655         if (!rt_mutex_owner(lock)) {
 656                 /*
 657                  * If the requeue [7] above changed the top waiter,
 658                  * then we need to wake the new top waiter up to try
 659                  * to get the lock.
 660                  */
 661                 if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
 662                         wake_up_process(rt_mutex_top_waiter(lock)->task);
 663                 raw_spin_unlock(&lock->wait_lock);
 664                 return 0;
 665         }
 666
 667         /* [10] Grab the next task, i.e. the owner of @lock */
 668         task = rt_mutex_owner(lock);
 669         get_task_struct(task);
 670         raw_spin_lock_irqsave(&task->pi_lock, flags);
 671
 672         /* [11] requeue the pi waiters if necessary */
 673         if (waiter == rt_mutex_top_waiter(lock)) {
 674                 /*
 675                  * The waiter became the new top (highest priority)
 676                  * waiter on the lock. Replace the previous top waiter
 677                  * in the owner tasks pi waiters tree with this waiter
 678                  * and adjust the priority of the owner.
 679                  */
 680                 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
 681                 rt_mutex_enqueue_pi(task, waiter);
 682                 __rt_mutex_adjust_prio(task);
 683
 684         } else if (prerequeue_top_waiter == waiter) {
 685                 /*
 686                  * The waiter was the top waiter on the lock, but is
 687                  * no longer the top prority waiter. Replace waiter in
 688                  * the owner tasks pi waiters tree with the new top
 689                  * (highest priority) waiter and adjust the priority
 690                  * of the owner.
 691                  * The new top waiter is stored in @waiter so that
 692                  * @waiter == @top_waiter evaluates to true below and
 693                  * we continue to deboost the rest of the chain.
 694                  */
 695                 rt_mutex_dequeue_pi(task, waiter);
 696                 waiter = rt_mutex_top_waiter(lock);
 697                 rt_mutex_enqueue_pi(task, waiter);
 698                 __rt_mutex_adjust_prio(task);
 699         } else {
 700                 /*
 701                  * Nothing changed. No need to do any priority
 702                  * adjustment.
 703                  */
 704         }
 705
 706         /*
 707          * [12] check_exit_conditions_4() protected by task->pi_lock
 708          * and lock->wait_lock. The actual decisions are made after we
 709          * dropped the locks.
 710          *
 711          * Check whether the task which owns the current lock is pi
 712          * blocked itself. If yes we store a pointer to the lock for
 713          * the lock chain change detection above. After we dropped
 714          * task->pi_lock next_lock cannot be dereferenced anymore.
 715          */
 716         next_lock = task_blocked_on_lock(task);
 717         /*
 718          * Store the top waiter of @lock for the end of chain walk
 719          * decision below.
 720          */
 721         top_waiter = rt_mutex_top_waiter(lock);
 722
 723         /* [13] Drop the locks */
 724         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 725         raw_spin_unlock(&lock->wait_lock);
 726
 727         /*
 728          * Make the actual exit decisions [12], based on the stored
 729          * values.
 730          *
 731          * We reached the end of the lock chain. Stop right here. No
 732          * point to go back just to figure that out.
 733          */
 734         if (!next_lock)
 735                 goto out_put_task;
 736
 737         /*
 738          * If the current waiter is not the top waiter on the lock,
 739          * then we can stop the chain walk here if we are not in full
 740          * deadlock detection mode.
 741          */
 742         if (!detect_deadlock && waiter != top_waiter)
 743                 goto out_put_task;
 744
 745         goto again;
 746
 747  out_unlock_pi:
 748         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 749  out_put_task:
 750         put_task_struct(task);
 751
 752         return ret;
 753 }
 754
 755 /*
 756  * Try to take an rt-mutex
 757  *
 758  * Must be called with lock->wait_lock held.
 759  *
 760  * @lock:   The lock to be acquired.
 761  * @task:   The task which wants to acquire the lock
 762  * @waiter: The waiter that is queued to the lock's wait tree if the
 763  *          callsite called task_blocked_on_lock(), otherwise NULL
 764  */
 765 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 766                                 struct rt_mutex_waiter *waiter)
 767 {
 768         unsigned long flags;
 769
 770         /*
 771          * Before testing whether we can acquire @lock, we set the
 772          * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
 773          * other tasks which try to modify @lock into the slow path
 774          * and they serialize on @lock->wait_lock.
 775          *
 776          * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
 777          * as explained at the top of this file if and only if:
 778          *
 779          * - There is a lock owner. The caller must fixup the
 780          *   transient state if it does a trylock or leaves the lock
 781          *   function due to a signal or timeout.
 782          *
 783          * - @task acquires the lock and there are no other
 784          *   waiters. This is undone in rt_mutex_set_owner(@task) at
 785          *   the end of this function.
 786          */
 787         mark_rt_mutex_waiters(lock);
 788
 789         /*
 790          * If @lock has an owner, give up.
 791          */
 792         if (rt_mutex_owner(lock))
 793                 return 0;
 794
 795         /*
 796          * If @waiter != NULL, @task has already enqueued the waiter
 797          * into @lock waiter tree. If @waiter == NULL then this is a
 798          * trylock attempt.
 799          */
 800         if (waiter) {
 801                 /*
 802                  * If waiter is not the highest priority waiter of
 803                  * @lock, give up.
 804                  */
 805                 if (waiter != rt_mutex_top_waiter(lock))
 806                         return 0;
 807
 808                 /*
 809                  * We can acquire the lock. Remove the waiter from the
 810                  * lock waiters tree.
 811                  */
 812                 rt_mutex_dequeue(lock, waiter);
 813
 814         } else {
 815                 /*
 816                  * If the lock has waiters already we check whether @task is
 817                  * eligible to take over the lock.
 818                  *
 819                  * If there are no other waiters, @task can acquire
 820                  * the lock.  @task->pi_blocked_on is NULL, so it does
 821                  * not need to be dequeued.
 822                  */
 823                 if (rt_mutex_has_waiters(lock)) {
 824                         /*
 825                          * If @task->prio is greater than or equal to
 826                          * the top waiter priority (kernel view),
 827                          * @task lost.
 828                          */
 829                         if (task->prio >= rt_mutex_top_waiter(lock)->prio)
 830                                 return 0;
 831
 832                         /*
 833                          * The current top waiter stays enqueued. We
 834                          * don't have to change anything in the lock
 835                          * waiters order.
 836                          */
 837                 } else {
 838                         /*
 839                          * No waiters. Take the lock without the
 840                          * pi_lock dance.@task->pi_blocked_on is NULL
 841                          * and we have no waiters to enqueue in @task
 842                          * pi waiters tree.
 843                          */
 844                         goto takeit;
 845                 }
 846         }
 847
 848         /*
 849          * Clear @task->pi_blocked_on. Requires protection by
 850          * @task->pi_lock. Redundant operation for the @waiter == NULL
 851          * case, but conditionals are more expensive than a redundant
 852          * store.
 853          */
 854         raw_spin_lock_irqsave(&task->pi_lock, flags);
 855         task->pi_blocked_on = NULL;
 856         /*
 857          * Finish the lock acquisition. @task is the new owner. If
 858          * other waiters exist we have to insert the highest priority
 859          * waiter into @task->pi_waiters tree.
 860          */
 861         if (rt_mutex_has_waiters(lock))
 862                 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
 863         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 864
 865 takeit:
 866         /* We got the lock. */
 867         debug_rt_mutex_lock(lock);
 868
 869         /*
 870          * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
 871          * are still waiters or clears it.
 872          */
 873         rt_mutex_set_owner(lock, task);
 874
 875         rt_mutex_deadlock_account_lock(lock, task);
 876
 877         return 1;
 878 }
 879
 880 /*
 881  * Task blocks on lock.
 882  *
 883  * Prepare waiter and propagate pi chain
 884  *
 885  * This must be called with lock->wait_lock held.
 886  */
 887 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 888                                    struct rt_mutex_waiter *waiter,
 889                                    struct task_struct *task,
 890                                    enum rtmutex_chainwalk chwalk)
 891 {
 892         struct task_struct *owner = rt_mutex_owner(lock);
 893         struct rt_mutex_waiter *top_waiter = waiter;
 894         struct rt_mutex *next_lock;
 895         int chain_walk = 0, res;
 896         unsigned long flags;
 897
 898         /*
 899          * Early deadlock detection. We really don't want the task to
 900          * enqueue on itself just to untangle the mess later. It's not
 901          * only an optimization. We drop the locks, so another waiter
 902          * can come in before the chain walk detects the deadlock. So
 903          * the other will detect the deadlock and return -EDEADLOCK,
 904          * which is wrong, as the other waiter is not in a deadlock
 905          * situation.
 906          */
 907         if (owner == task)
 908                 return -EDEADLK;
 909
 910         raw_spin_lock_irqsave(&task->pi_lock, flags);
 911         __rt_mutex_adjust_prio(task);
 912         waiter->task = task;
 913         waiter->lock = lock;
 914         waiter->prio = task->prio;
 915
 916         /* Get the top priority waiter on the lock */
 917         if (rt_mutex_has_waiters(lock))
 918                 top_waiter = rt_mutex_top_waiter(lock);
 919         rt_mutex_enqueue(lock, waiter);
 920
 921         task->pi_blocked_on = waiter;
 922
 923         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 924
 925         if (!owner)
 926                 return 0;
 927
 928         raw_spin_lock_irqsave(&owner->pi_lock, flags);
 929         if (waiter == rt_mutex_top_waiter(lock)) {
 930                 rt_mutex_dequeue_pi(owner, top_waiter);
 931                 rt_mutex_enqueue_pi(owner, waiter);
 932
 933                 __rt_mutex_adjust_prio(owner);
 934                 if (owner->pi_blocked_on)
 935                         chain_walk = 1;
 936         } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
 937                 chain_walk = 1;
 938         }
 939
 940         /* Store the lock on which owner is blocked or NULL */
 941         next_lock = task_blocked_on_lock(owner);
 942
 943         raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 944         /*
 945          * Even if full deadlock detection is on, if the owner is not
 946          * blocked itself, we can avoid finding this out in the chain
 947          * walk.
 948          */
 949         if (!chain_walk || !next_lock)
 950                 return 0;
 951
 952         /*
 953          * The owner can't disappear while holding a lock,
 954          * so the owner struct is protected by wait_lock.
 955          * Gets dropped in rt_mutex_adjust_prio_chain()!
 956          */
 957         get_task_struct(owner);
 958
 959         raw_spin_unlock(&lock->wait_lock);
 960
 961         res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
 962                                          next_lock, waiter, task);
 963
 964         raw_spin_lock(&lock->wait_lock);
 965
 966         return res;
 967 }
 968
 969 /*
 970  * Remove the top waiter from the current tasks pi waiter tree and
 971  * queue it up.
 972  *
 973  * Called with lock->wait_lock held.
 974  */
 975 static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
 976                                     struct rt_mutex *lock)
 977 {
 978         struct rt_mutex_waiter *waiter;
 979         unsigned long flags;
 980
 981         raw_spin_lock_irqsave(&current->pi_lock, flags);
 982
 983         waiter = rt_mutex_top_waiter(lock);
 984
 985         /*
 986          * Remove it from current->pi_waiters. We do not adjust a
 987          * possible priority boost right now. We execute wakeup in the
 988          * boosted mode and go back to normal after releasing
 989          * lock->wait_lock.
 990          */
 991         rt_mutex_dequeue_pi(current, waiter);
 992
 993         /*
 994          * As we are waking up the top waiter, and the waiter stays
 995          * queued on the lock until it gets the lock, this lock
 996          * obviously has waiters. Just set the bit here and this has
 997          * the added benefit of forcing all new tasks into the
 998          * slow path making sure no task of lower priority than
 999          * the top waiter can steal this lock.
1000          */
1001         lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1002
1003         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
1004
1005         wake_q_add(wake_q, waiter->task);
1006 }
1007
1008 /*
1009  * Remove a waiter from a lock and give up
1010  *
1011  * Must be called with lock->wait_lock held and
1012  * have just failed to try_to_take_rt_mutex().
1013  */
1014 static void remove_waiter(struct rt_mutex *lock,
1015                           struct rt_mutex_waiter *waiter)
1016 {
1017         bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1018         struct task_struct *owner = rt_mutex_owner(lock);
1019         struct rt_mutex *next_lock;
1020         unsigned long flags;
1021
1022         raw_spin_lock_irqsave(&current->pi_lock, flags);
1023         rt_mutex_dequeue(lock, waiter);
1024         current->pi_blocked_on = NULL;
1025         raw_spin_unlock_irqrestore(&current->pi_lock, flags);
1026
1027         /*
1028          * Only update priority if the waiter was the highest priority
1029          * waiter of the lock and there is an owner to update.
1030          */
1031         if (!owner || !is_top_waiter)
1032                 return;
1033
1034         raw_spin_lock_irqsave(&owner->pi_lock, flags);
1035
1036         rt_mutex_dequeue_pi(owner, waiter);
1037
1038         if (rt_mutex_has_waiters(lock))
1039                 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1040
1041         __rt_mutex_adjust_prio(owner);
1042
1043         /* Store the lock on which owner is blocked or NULL */
1044         next_lock = task_blocked_on_lock(owner);
1045
1046         raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
1047
1048         /*
1049          * Don't walk the chain, if the owner task is not blocked
1050          * itself.
1051          */
1052         if (!next_lock)
1053                 return;
1054
1055         /* gets dropped in rt_mutex_adjust_prio_chain()! */
1056         get_task_struct(owner);
1057
1058         raw_spin_unlock(&lock->wait_lock);
1059
1060         rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1061                                    next_lock, NULL, current);
1062
1063         raw_spin_lock(&lock->wait_lock);
1064 }
1065
1066 /*
1067  * Recheck the pi chain, in case we got a priority setting
1068  *
1069  * Called from sched_setscheduler
1070  */
1071 void rt_mutex_adjust_pi(struct task_struct *task)
1072 {
1073         struct rt_mutex_waiter *waiter;
1074         struct rt_mutex *next_lock;
1075         unsigned long flags;
1076
1077         raw_spin_lock_irqsave(&task->pi_lock, flags);
1078
1079         waiter = task->pi_blocked_on;
1080         if (!waiter || (waiter->prio == task->prio &&
1081                         !dl_prio(task->prio))) {
1082                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1083                 return;
1084         }
1085         next_lock = waiter->lock;
1086         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1087
1088         /* gets dropped in rt_mutex_adjust_prio_chain()! */
1089         get_task_struct(task);
1090
1091         rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1092                                    next_lock, NULL, task);
1093 }
1094
1095 /**
1096  * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1097  * @lock:                the rt_mutex to take
1098  * @state:               the state the task should block in (TASK_INTERRUPTIBLE
1099  *                       or TASK_UNINTERRUPTIBLE)
1100  * @timeout:             the pre-initialized and started timer, or NULL for none
1101  * @waiter:              the pre-initialized rt_mutex_waiter
1102  *
1103  * lock->wait_lock must be held by the caller.
1104  */
1105 static int __sched
1106 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
1107                     struct hrtimer_sleeper *timeout,
1108                     struct rt_mutex_waiter *waiter)
1109 {
1110         int ret = 0;
1111
1112         for (;;) {
1113                 /* Try to acquire the lock: */
1114                 if (try_to_take_rt_mutex(lock, current, waiter))
1115                         break;
1116
1117                 /*
1118                  * TASK_INTERRUPTIBLE checks for signals and
1119                  * timeout. Ignored otherwise.
1120                  */
1121                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
1122                         /* Signal pending? */
1123                         if (signal_pending(current))
1124                                 ret = -EINTR;
1125                         if (timeout && !timeout->task)
1126                                 ret = -ETIMEDOUT;
1127                         if (ret)
1128                                 break;
1129                 }
1130
1131                 raw_spin_unlock(&lock->wait_lock);
1132
1133                 debug_rt_mutex_print_deadlock(waiter);
1134
1135                 schedule();
1136
1137                 raw_spin_lock(&lock->wait_lock);
1138                 set_current_state(state);
1139         }
1140
1141         __set_current_state(TASK_RUNNING);
1142         return ret;
1143 }
1144
1145 static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1146                                      struct rt_mutex_waiter *w)
1147 {
1148         /*
1149          * If the result is not -EDEADLOCK or the caller requested
1150          * deadlock detection, nothing to do here.
1151          */
1152         if (res != -EDEADLOCK || detect_deadlock)
1153                 return;
1154
1155         /*
1156          * Yell lowdly and stop the task right here.
1157          */
1158         rt_mutex_print_deadlock(w);
1159         while (1) {
1160                 set_current_state(TASK_INTERRUPTIBLE);
1161                 schedule();
1162         }
1163 }
1164
1165 /*
1166  * Slow path lock function:
1167  */
1168 static int __sched
1169 rt_mutex_slowlock(struct rt_mutex *lock, int state,
1170                   struct hrtimer_sleeper *timeout,
1171                   enum rtmutex_chainwalk chwalk)
1172 {
1173         struct rt_mutex_waiter waiter;
1174         int ret = 0;
1175
1176         debug_rt_mutex_init_waiter(&waiter);
1177         RB_CLEAR_NODE(&waiter.pi_tree_entry);
1178         RB_CLEAR_NODE(&waiter.tree_entry);
1179
1180         raw_spin_lock(&lock->wait_lock);
1181
1182         /* Try to acquire the lock again: */
1183         if (try_to_take_rt_mutex(lock, current, NULL)) {
1184                 raw_spin_unlock(&lock->wait_lock);
1185                 return 0;
1186         }
1187
1188         set_current_state(state);
1189
1190         /* Setup the timer, when timeout != NULL */
1191         if (unlikely(timeout))
1192                 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1193
1194         ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1195
1196         if (likely(!ret))
1197                 /* sleep on the mutex */
1198                 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1199
1200         if (unlikely(ret)) {
1201                 __set_current_state(TASK_RUNNING);
1202                 if (rt_mutex_has_waiters(lock))
1203                         remove_waiter(lock, &waiter);
1204                 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1205         }
1206
1207         /*
1208          * try_to_take_rt_mutex() sets the waiter bit
1209          * unconditionally. We might have to fix that up.
1210          */
1211         fixup_rt_mutex_waiters(lock);
1212
1213         raw_spin_unlock(&lock->wait_lock);
1214
1215         /* Remove pending timer: */
1216         if (unlikely(timeout))
1217                 hrtimer_cancel(&timeout->timer);
1218
1219         debug_rt_mutex_free_waiter(&waiter);
1220
1221         return ret;
1222 }
1223
1224 /*
1225  * Slow path try-lock function:
1226  */
1227 static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1228 {
1229         int ret;
1230
1231         /*
1232          * If the lock already has an owner we fail to get the lock.
1233          * This can be done without taking the @lock->wait_lock as
1234          * it is only being read, and this is a trylock anyway.
1235          */
1236         if (rt_mutex_owner(lock))
1237                 return 0;
1238
1239         /*
1240          * The mutex has currently no owner. Lock the wait lock and
1241          * try to acquire the lock.
1242          */
1243         raw_spin_lock(&lock->wait_lock);
1244
1245         ret = try_to_take_rt_mutex(lock, current, NULL);
1246
1247         /*
1248          * try_to_take_rt_mutex() sets the lock waiters bit
1249          * unconditionally. Clean this up.
1250          */
1251         fixup_rt_mutex_waiters(lock);
1252
1253         raw_spin_unlock(&lock->wait_lock);
1254
1255         return ret;
1256 }
1257
1258 /*
1259  * Slow path to release a rt-mutex.
1260  * Return whether the current task needs to undo a potential priority boosting.
1261  */
1262 static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1263                                         struct wake_q_head *wake_q)
1264 {
1265         raw_spin_lock(&lock->wait_lock);
1266
1267         debug_rt_mutex_unlock(lock);
1268
1269         rt_mutex_deadlock_account_unlock(current);
1270
1271         /*
1272          * We must be careful here if the fast path is enabled. If we
1273          * have no waiters queued we cannot set owner to NULL here
1274          * because of:
1275          *
1276          * foo->lock->owner = NULL;
1277          *                      rtmutex_lock(foo->lock);   <- fast path
1278          *                      free = atomic_dec_and_test(foo->refcnt);
1279          *                      rtmutex_unlock(foo->lock); <- fast path
1280          *                      if (free)
1281          *                              kfree(foo);
1282          * raw_spin_unlock(foo->lock->wait_lock);
1283          *
1284          * So for the fastpath enabled kernel:
1285          *
1286          * Nothing can set the waiters bit as long as we hold
1287          * lock->wait_lock. So we do the following sequence:
1288          *
1289          *      owner = rt_mutex_owner(lock);
1290          *      clear_rt_mutex_waiters(lock);
1291          *      raw_spin_unlock(&lock->wait_lock);
1292          *      if (cmpxchg(&lock->owner, owner, 0) == owner)
1293          *              return;
1294          *      goto retry;
1295          *
1296          * The fastpath disabled variant is simple as all access to
1297          * lock->owner is serialized by lock->wait_lock:
1298          *
1299          *      lock->owner = NULL;
1300          *      raw_spin_unlock(&lock->wait_lock);
1301          */
1302         while (!rt_mutex_has_waiters(lock)) {
1303                 /* Drops lock->wait_lock ! */
1304                 if (unlock_rt_mutex_safe(lock) == true)
1305                         return false;
1306                 /* Relock the rtmutex and try again */
1307                 raw_spin_lock(&lock->wait_lock);
1308         }
1309
1310         /*
1311          * The wakeup next waiter path does not suffer from the above
1312          * race. See the comments there.
1313          *
1314          * Queue the next waiter for wakeup once we release the wait_lock.
1315          */
1316         mark_wakeup_next_waiter(wake_q, lock);
1317
1318         raw_spin_unlock(&lock->wait_lock);
1319
1320         /* check PI boosting */
1321         return true;
1322 }
1323
1324 /*
1325  * debug aware fast / slowpath lock,trylock,unlock
1326  *
1327  * The atomic acquire/release ops are compiled away, when either the
1328  * architecture does not support cmpxchg or when debugging is enabled.
1329  */
1330 static inline int
1331 rt_mutex_fastlock(struct rt_mutex *lock, int state,
1332                   int (*slowfn)(struct rt_mutex *lock, int state,
1333                                 struct hrtimer_sleeper *timeout,
1334                                 enum rtmutex_chainwalk chwalk))
1335 {
1336         if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1337                 rt_mutex_deadlock_account_lock(lock, current);
1338                 return 0;
1339         } else
1340                 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1341 }
1342
1343 static inline int
1344 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1345                         struct hrtimer_sleeper *timeout,
1346                         enum rtmutex_chainwalk chwalk,
1347                         int (*slowfn)(struct rt_mutex *lock, int state,
1348                                       struct hrtimer_sleeper *timeout,
1349                                       enum rtmutex_chainwalk chwalk))
1350 {
1351         if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1352             likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1353                 rt_mutex_deadlock_account_lock(lock, current);
1354                 return 0;
1355         } else
1356                 return slowfn(lock, state, timeout, chwalk);
1357 }
1358
1359 static inline int
1360 rt_mutex_fasttrylock(struct rt_mutex *lock,
1361                      int (*slowfn)(struct rt_mutex *lock))
1362 {
1363         if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1364                 rt_mutex_deadlock_account_lock(lock, current);
1365                 return 1;
1366         }
1367         return slowfn(lock);
1368 }
1369
1370 static inline void
1371 rt_mutex_fastunlock(struct rt_mutex *lock,
1372                     bool (*slowfn)(struct rt_mutex *lock,
1373                                    struct wake_q_head *wqh))
1374 {
1375         WAKE_Q(wake_q);
1376
1377         if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
1378                 rt_mutex_deadlock_account_unlock(current);
1379
1380         } else {
1381                 bool deboost = slowfn(lock, &wake_q);
1382
1383                 wake_up_q(&wake_q);
1384
1385                 /* Undo pi boosting if necessary: */
1386                 if (deboost)
1387                         rt_mutex_adjust_prio(current);
1388         }
1389 }
1390
1391 /**
1392  * rt_mutex_lock - lock a rt_mutex
1393  *
1394  * @lock: the rt_mutex to be locked
1395  */
1396 void __sched rt_mutex_lock(struct rt_mutex *lock)
1397 {
1398         might_sleep();
1399
1400         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1401 }
1402 EXPORT_SYMBOL_GPL(rt_mutex_lock);
1403
1404 /**
1405  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1406  *
1407  * @lock:               the rt_mutex to be locked
1408  *
1409  * Returns:
1410  *  0           on success
1411  * -EINTR       when interrupted by a signal
1412  */
1413 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1414 {
1415         might_sleep();
1416
1417         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1418 }
1419 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1420
1421 /*
1422  * Futex variant with full deadlock detection.
1423  */
1424 int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
1425                               struct hrtimer_sleeper *timeout)
1426 {
1427         might_sleep();
1428
1429         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1430                                        RT_MUTEX_FULL_CHAINWALK,
1431                                        rt_mutex_slowlock);
1432 }
1433
1434 /**
1435  * rt_mutex_timed_lock - lock a rt_mutex interruptible
1436  *                      the timeout structure is provided
1437  *                      by the caller
1438  *
1439  * @lock:               the rt_mutex to be locked
1440  * @timeout:            timeout structure or NULL (no timeout)
1441  *
1442  * Returns:
1443  *  0           on success
1444  * -EINTR       when interrupted by a signal
1445  * -ETIMEDOUT   when the timeout expired
1446  */
1447 int
1448 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1449 {
1450         might_sleep();
1451
1452         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1453                                        RT_MUTEX_MIN_CHAINWALK,
1454                                        rt_mutex_slowlock);
1455 }
1456 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1457
1458 /**
1459  * rt_mutex_trylock - try to lock a rt_mutex
1460  *
1461  * @lock:       the rt_mutex to be locked
1462  *
1463  * This function can only be called in thread context. It's safe to
1464  * call it from atomic regions, but not from hard interrupt or soft
1465  * interrupt context.
1466  *
1467  * Returns 1 on success and 0 on contention
1468  */
1469 int __sched rt_mutex_trylock(struct rt_mutex *lock)
1470 {
1471         if (WARN_ON(in_irq() || in_nmi() || in_serving_softirq()))
1472                 return 0;
1473
1474         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1475 }
1476 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1477
1478 /**
1479  * rt_mutex_unlock - unlock a rt_mutex
1480  *
1481  * @lock: the rt_mutex to be unlocked
1482  */
1483 void __sched rt_mutex_unlock(struct rt_mutex *lock)
1484 {
1485         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1486 }
1487 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1488
1489 /**
1490  * rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock
1491  * @lock: the rt_mutex to be unlocked
1492  *
1493  * Returns: true/false indicating whether priority adjustment is
1494  * required or not.
1495  */
1496 bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
1497                                    struct wake_q_head *wqh)
1498 {
1499         if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
1500                 rt_mutex_deadlock_account_unlock(current);
1501                 return false;
1502         }
1503         return rt_mutex_slowunlock(lock, wqh);
1504 }
1505
1506 /**
1507  * rt_mutex_destroy - mark a mutex unusable
1508  * @lock: the mutex to be destroyed
1509  *
1510  * This function marks the mutex uninitialized, and any subsequent
1511  * use of the mutex is forbidden. The mutex must not be locked when
1512  * this function is called.
1513  */
1514 void rt_mutex_destroy(struct rt_mutex *lock)
1515 {
1516         WARN_ON(rt_mutex_is_locked(lock));
1517 #ifdef CONFIG_DEBUG_RT_MUTEXES
1518         lock->magic = NULL;
1519 #endif
1520 }
1521
1522 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1523
1524 /**
1525  * __rt_mutex_init - initialize the rt lock
1526  *
1527  * @lock: the rt lock to be initialized
1528  *
1529  * Initialize the rt lock to unlocked state.
1530  *
1531  * Initializing of a locked rt lock is not allowed
1532  */
1533 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1534 {
1535         lock->owner = NULL;
1536         raw_spin_lock_init(&lock->wait_lock);
1537         lock->waiters = RB_ROOT;
1538         lock->waiters_leftmost = NULL;
1539
1540         debug_rt_mutex_init(lock, name);
1541 }
1542 EXPORT_SYMBOL_GPL(__rt_mutex_init);
1543
1544 /**
1545  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1546  *                              proxy owner
1547  *
1548  * @lock:       the rt_mutex to be locked
1549  * @proxy_owner:the task to set as owner
1550  *
1551  * No locking. Caller has to do serializing itself
1552  * Special API call for PI-futex support
1553  */
1554 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1555                                 struct task_struct *proxy_owner)
1556 {
1557         __rt_mutex_init(lock, NULL);
1558         debug_rt_mutex_proxy_lock(lock, proxy_owner);
1559         rt_mutex_set_owner(lock, proxy_owner);
1560         rt_mutex_deadlock_account_lock(lock, proxy_owner);
1561 }
1562
1563 /**
1564  * rt_mutex_proxy_unlock - release a lock on behalf of owner
1565  *
1566  * @lock:       the rt_mutex to be locked
1567  *
1568  * No locking. Caller has to do serializing itself
1569  * Special API call for PI-futex support
1570  */
1571 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1572                            struct task_struct *proxy_owner)
1573 {
1574         debug_rt_mutex_proxy_unlock(lock);
1575         rt_mutex_set_owner(lock, NULL);
1576         rt_mutex_deadlock_account_unlock(proxy_owner);
1577 }
1578
1579 /**
1580  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1581  * @lock:               the rt_mutex to take
1582  * @waiter:             the pre-initialized rt_mutex_waiter
1583  * @task:               the task to prepare
1584  *
1585  * Returns:
1586  *  0 - task blocked on lock
1587  *  1 - acquired the lock for task, caller should wake it up
1588  * <0 - error
1589  *
1590  * Special API call for FUTEX_REQUEUE_PI support.
1591  */
1592 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1593                               struct rt_mutex_waiter *waiter,
1594                               struct task_struct *task)
1595 {
1596         int ret;
1597
1598         raw_spin_lock(&lock->wait_lock);
1599
1600         if (try_to_take_rt_mutex(lock, task, NULL)) {
1601                 raw_spin_unlock(&lock->wait_lock);
1602                 return 1;
1603         }
1604
1605         /* We enforce deadlock detection for futexes */
1606         ret = task_blocks_on_rt_mutex(lock, waiter, task,
1607                                       RT_MUTEX_FULL_CHAINWALK);
1608
1609         if (ret && !rt_mutex_owner(lock)) {
1610                 /*
1611                  * Reset the return value. We might have
1612                  * returned with -EDEADLK and the owner
1613                  * released the lock while we were walking the
1614                  * pi chain.  Let the waiter sort it out.
1615                  */
1616                 ret = 0;
1617         }
1618
1619         if (unlikely(ret))
1620                 remove_waiter(lock, waiter);
1621
1622         raw_spin_unlock(&lock->wait_lock);
1623
1624         debug_rt_mutex_print_deadlock(waiter);
1625
1626         return ret;
1627 }
1628
1629 /**
1630  * rt_mutex_next_owner - return the next owner of the lock
1631  *
1632  * @lock: the rt lock query
1633  *
1634  * Returns the next owner of the lock or NULL
1635  *
1636  * Caller has to serialize against other accessors to the lock
1637  * itself.
1638  *
1639  * Special API call for PI-futex support
1640  */
1641 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1642 {
1643         if (!rt_mutex_has_waiters(lock))
1644                 return NULL;
1645
1646         return rt_mutex_top_waiter(lock)->task;
1647 }
1648
1649 /**
1650  * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1651  * @lock:               the rt_mutex we were woken on
1652  * @to:                 the timeout, null if none. hrtimer should already have
1653  *                      been started.
1654  * @waiter:             the pre-initialized rt_mutex_waiter
1655  *
1656  * Complete the lock acquisition started our behalf by another thread.
1657  *
1658  * Returns:
1659  *  0 - success
1660  * <0 - error, one of -EINTR, -ETIMEDOUT
1661  *
1662  * Special API call for PI-futex requeue support
1663  */
1664 int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1665                                struct hrtimer_sleeper *to,
1666                                struct rt_mutex_waiter *waiter)
1667 {
1668         int ret;
1669
1670         raw_spin_lock(&lock->wait_lock);
1671
1672         set_current_state(TASK_INTERRUPTIBLE);
1673
1674         /* sleep on the mutex */
1675         ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1676
1677         if (unlikely(ret))
1678                 remove_waiter(lock, waiter);
1679
1680         /*
1681          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1682          * have to fix that up.
1683          */
1684         fixup_rt_mutex_waiters(lock);
1685
1686         raw_spin_unlock(&lock->wait_lock);
1687
1688         return ret;
1689 }