kernel/locking/rtmutex_api.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * rtmutex API
   4  */
   5 #include <linux/spinlock.h>
   6 #include <linux/export.h>
   7
   8 #define RT_MUTEX_BUILD_MUTEX
   9 #include "rtmutex.c"
  10
  11 /*
  12  * Max number of times we'll walk the boosting chain:
  13  */
  14 int max_lock_depth = 1024;
  15
  16 /*
  17  * Debug aware fast / slowpath lock,trylock,unlock
  18  *
  19  * The atomic acquire/release ops are compiled away, when either the
  20  * architecture does not support cmpxchg or when debugging is enabled.
  21  */
  22 static __always_inline int __rt_mutex_lock_common(struct rt_mutex *lock,
  23                                                   unsigned int state,
  24                                                   unsigned int subclass)
  25 {
  26         int ret;
  27
  28         might_sleep();
  29         mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
  30         ret = __rt_mutex_lock(&lock->rtmutex, state);
  31         if (ret)
  32                 mutex_release(&lock->dep_map, _RET_IP_);
  33         return ret;
  34 }
  35
  36 void rt_mutex_base_init(struct rt_mutex_base *rtb)
  37 {
  38         __rt_mutex_base_init(rtb);
  39 }
  40 EXPORT_SYMBOL(rt_mutex_base_init);
  41
  42 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  43 /**
  44  * rt_mutex_lock_nested - lock a rt_mutex
  45  *
  46  * @lock: the rt_mutex to be locked
  47  * @subclass: the lockdep subclass
  48  */
  49 void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
  50 {
  51         __rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass);
  52 }
  53 EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
  54
  55 #else /* !CONFIG_DEBUG_LOCK_ALLOC */
  56
  57 /**
  58  * rt_mutex_lock - lock a rt_mutex
  59  *
  60  * @lock: the rt_mutex to be locked
  61  */
  62 void __sched rt_mutex_lock(struct rt_mutex *lock)
  63 {
  64         __rt_mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0);
  65 }
  66 EXPORT_SYMBOL_GPL(rt_mutex_lock);
  67 #endif
  68
  69 /**
  70  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
  71  *
  72  * @lock:               the rt_mutex to be locked
  73  *
  74  * Returns:
  75  *  0           on success
  76  * -EINTR       when interrupted by a signal
  77  */
  78 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
  79 {
  80         return __rt_mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0);
  81 }
  82 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
  83
  84 /**
  85  * rt_mutex_trylock - try to lock a rt_mutex
  86  *
  87  * @lock:       the rt_mutex to be locked
  88  *
  89  * This function can only be called in thread context. It's safe to call it
  90  * from atomic regions, but not from hard or soft interrupt context.
  91  *
  92  * Returns:
  93  *  1 on success
  94  *  0 on contention
  95  */
  96 int __sched rt_mutex_trylock(struct rt_mutex *lock)
  97 {
  98         int ret;
  99
 100         if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES) && WARN_ON_ONCE(!in_task()))
 101                 return 0;
 102
 103         ret = __rt_mutex_trylock(&lock->rtmutex);
 104         if (ret)
 105                 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 106
 107         return ret;
 108 }
 109 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
 110
 111 /**
 112  * rt_mutex_unlock - unlock a rt_mutex
 113  *
 114  * @lock: the rt_mutex to be unlocked
 115  */
 116 void __sched rt_mutex_unlock(struct rt_mutex *lock)
 117 {
 118         mutex_release(&lock->dep_map, _RET_IP_);
 119         __rt_mutex_unlock(&lock->rtmutex);
 120 }
 121 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
 122
 123 /*
 124  * Futex variants, must not use fastpath.
 125  */
 126 int __sched rt_mutex_futex_trylock(struct rt_mutex_base *lock)
 127 {
 128         return rt_mutex_slowtrylock(lock);
 129 }
 130
 131 int __sched __rt_mutex_futex_trylock(struct rt_mutex_base *lock)
 132 {
 133         return __rt_mutex_slowtrylock(lock);
 134 }
 135
 136 /**
 137  * __rt_mutex_futex_unlock - Futex variant, that since futex variants
 138  * do not use the fast-path, can be simple and will not need to retry.
 139  *
 140  * @lock:       The rt_mutex to be unlocked
 141  * @wqh:        The wake queue head from which to get the next lock waiter
 142  */
 143 bool __sched __rt_mutex_futex_unlock(struct rt_mutex_base *lock,
 144                                      struct rt_wake_q_head *wqh)
 145 {
 146         lockdep_assert_held(&lock->wait_lock);
 147
 148         debug_rt_mutex_unlock(lock);
 149
 150         if (!rt_mutex_has_waiters(lock)) {
 151                 lock->owner = NULL;
 152                 return false; /* done */
 153         }
 154
 155         /*
 156          * We've already deboosted, mark_wakeup_next_waiter() will
 157          * retain preempt_disabled when we drop the wait_lock, to
 158          * avoid inversion prior to the wakeup.  preempt_disable()
 159          * therein pairs with rt_mutex_postunlock().
 160          */
 161         mark_wakeup_next_waiter(wqh, lock);
 162
 163         return true; /* call postunlock() */
 164 }
 165
 166 void __sched rt_mutex_futex_unlock(struct rt_mutex_base *lock)
 167 {
 168         DEFINE_RT_WAKE_Q(wqh);
 169         unsigned long flags;
 170         bool postunlock;
 171
 172         raw_spin_lock_irqsave(&lock->wait_lock, flags);
 173         postunlock = __rt_mutex_futex_unlock(lock, &wqh);
 174         raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 175
 176         if (postunlock)
 177                 rt_mutex_postunlock(&wqh);
 178 }
 179
 180 /**
 181  * __rt_mutex_init - initialize the rt_mutex
 182  *
 183  * @lock:       The rt_mutex to be initialized
 184  * @name:       The lock name used for debugging
 185  * @key:        The lock class key used for debugging
 186  *
 187  * Initialize the rt_mutex to unlocked state.
 188  *
 189  * Initializing of a locked rt_mutex is not allowed
 190  */
 191 void __sched __rt_mutex_init(struct rt_mutex *lock, const char *name,
 192                              struct lock_class_key *key)
 193 {
 194         debug_check_no_locks_freed((void *)lock, sizeof(*lock));
 195         __rt_mutex_base_init(&lock->rtmutex);
 196         lockdep_init_map_wait(&lock->dep_map, name, key, 0, LD_WAIT_SLEEP);
 197 }
 198 EXPORT_SYMBOL_GPL(__rt_mutex_init);
 199
 200 /**
 201  * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
 202  *                              proxy owner
 203  *
 204  * @lock:       the rt_mutex to be locked
 205  * @proxy_owner:the task to set as owner
 206  *
 207  * No locking. Caller has to do serializing itself
 208  *
 209  * Special API call for PI-futex support. This initializes the rtmutex and
 210  * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
 211  * possible at this point because the pi_state which contains the rtmutex
 212  * is not yet visible to other tasks.
 213  */
 214 void __sched rt_mutex_init_proxy_locked(struct rt_mutex_base *lock,
 215                                         struct task_struct *proxy_owner)
 216 {
 217         __rt_mutex_base_init(lock);
 218         rt_mutex_set_owner(lock, proxy_owner);
 219 }
 220
 221 /**
 222  * rt_mutex_proxy_unlock - release a lock on behalf of owner
 223  *
 224  * @lock:       the rt_mutex to be locked
 225  *
 226  * No locking. Caller has to do serializing itself
 227  *
 228  * Special API call for PI-futex support. This just cleans up the rtmutex
 229  * (debugging) state. Concurrent operations on this rt_mutex are not
 230  * possible because it belongs to the pi_state which is about to be freed
 231  * and it is not longer visible to other tasks.
 232  */
 233 void __sched rt_mutex_proxy_unlock(struct rt_mutex_base *lock)
 234 {
 235         debug_rt_mutex_proxy_unlock(lock);
 236         rt_mutex_set_owner(lock, NULL);
 237 }
 238
 239 /**
 240  * __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
 241  * @lock:               the rt_mutex to take
 242  * @waiter:             the pre-initialized rt_mutex_waiter
 243  * @task:               the task to prepare
 244  *
 245  * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
 246  * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
 247  *
 248  * NOTE: does _NOT_ remove the @waiter on failure; must either call
 249  * rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
 250  *
 251  * Returns:
 252  *  0 - task blocked on lock
 253  *  1 - acquired the lock for task, caller should wake it up
 254  * <0 - error
 255  *
 256  * Special API call for PI-futex support.
 257  */
 258 int __sched __rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
 259                                         struct rt_mutex_waiter *waiter,
 260                                         struct task_struct *task)
 261 {
 262         int ret;
 263
 264         lockdep_assert_held(&lock->wait_lock);
 265
 266         if (try_to_take_rt_mutex(lock, task, NULL))
 267                 return 1;
 268
 269         /* We enforce deadlock detection for futexes */
 270         ret = task_blocks_on_rt_mutex(lock, waiter, task, NULL,
 271                                       RT_MUTEX_FULL_CHAINWALK);
 272
 273         if (ret && !rt_mutex_owner(lock)) {
 274                 /*
 275                  * Reset the return value. We might have
 276                  * returned with -EDEADLK and the owner
 277                  * released the lock while we were walking the
 278                  * pi chain.  Let the waiter sort it out.
 279                  */
 280                 ret = 0;
 281         }
 282
 283         return ret;
 284 }
 285
 286 /**
 287  * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
 288  * @lock:               the rt_mutex to take
 289  * @waiter:             the pre-initialized rt_mutex_waiter
 290  * @task:               the task to prepare
 291  *
 292  * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
 293  * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
 294  *
 295  * NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
 296  * on failure.
 297  *
 298  * Returns:
 299  *  0 - task blocked on lock
 300  *  1 - acquired the lock for task, caller should wake it up
 301  * <0 - error
 302  *
 303  * Special API call for PI-futex support.
 304  */
 305 int __sched rt_mutex_start_proxy_lock(struct rt_mutex_base *lock,
 306                                       struct rt_mutex_waiter *waiter,
 307                                       struct task_struct *task)
 308 {
 309         int ret;
 310
 311         raw_spin_lock_irq(&lock->wait_lock);
 312         ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
 313         if (unlikely(ret))
 314                 remove_waiter(lock, waiter);
 315         raw_spin_unlock_irq(&lock->wait_lock);
 316
 317         return ret;
 318 }
 319
 320 /**
 321  * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
 322  * @lock:               the rt_mutex we were woken on
 323  * @to:                 the timeout, null if none. hrtimer should already have
 324  *                      been started.
 325  * @waiter:             the pre-initialized rt_mutex_waiter
 326  *
 327  * Wait for the lock acquisition started on our behalf by
 328  * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
 329  * rt_mutex_cleanup_proxy_lock().
 330  *
 331  * Returns:
 332  *  0 - success
 333  * <0 - error, one of -EINTR, -ETIMEDOUT
 334  *
 335  * Special API call for PI-futex support
 336  */
 337 int __sched rt_mutex_wait_proxy_lock(struct rt_mutex_base *lock,
 338                                      struct hrtimer_sleeper *to,
 339                                      struct rt_mutex_waiter *waiter)
 340 {
 341         int ret;
 342
 343         raw_spin_lock_irq(&lock->wait_lock);
 344         /* sleep on the mutex */
 345         set_current_state(TASK_INTERRUPTIBLE);
 346         ret = rt_mutex_slowlock_block(lock, NULL, TASK_INTERRUPTIBLE, to, waiter);
 347         /*
 348          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 349          * have to fix that up.
 350          */
 351         fixup_rt_mutex_waiters(lock);
 352         raw_spin_unlock_irq(&lock->wait_lock);
 353
 354         return ret;
 355 }
 356
 357 /**
 358  * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
 359  * @lock:               the rt_mutex we were woken on
 360  * @waiter:             the pre-initialized rt_mutex_waiter
 361  *
 362  * Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
 363  * rt_mutex_wait_proxy_lock().
 364  *
 365  * Unless we acquired the lock; we're still enqueued on the wait-list and can
 366  * in fact still be granted ownership until we're removed. Therefore we can
 367  * find we are in fact the owner and must disregard the
 368  * rt_mutex_wait_proxy_lock() failure.
 369  *
 370  * Returns:
 371  *  true  - did the cleanup, we done.
 372  *  false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
 373  *          caller should disregards its return value.
 374  *
 375  * Special API call for PI-futex support
 376  */
 377 bool __sched rt_mutex_cleanup_proxy_lock(struct rt_mutex_base *lock,
 378                                          struct rt_mutex_waiter *waiter)
 379 {
 380         bool cleanup = false;
 381
 382         raw_spin_lock_irq(&lock->wait_lock);
 383         /*
 384          * Do an unconditional try-lock, this deals with the lock stealing
 385          * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
 386          * sets a NULL owner.
 387          *
 388          * We're not interested in the return value, because the subsequent
 389          * test on rt_mutex_owner() will infer that. If the trylock succeeded,
 390          * we will own the lock and it will have removed the waiter. If we
 391          * failed the trylock, we're still not owner and we need to remove
 392          * ourselves.
 393          */
 394         try_to_take_rt_mutex(lock, current, waiter);
 395         /*
 396          * Unless we're the owner; we're still enqueued on the wait_list.
 397          * So check if we became owner, if not, take us off the wait_list.
 398          */
 399         if (rt_mutex_owner(lock) != current) {
 400                 remove_waiter(lock, waiter);
 401                 cleanup = true;
 402         }
 403         /*
 404          * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
 405          * have to fix that up.
 406          */
 407         fixup_rt_mutex_waiters(lock);
 408
 409         raw_spin_unlock_irq(&lock->wait_lock);
 410
 411         return cleanup;
 412 }
 413
 414 /*
 415  * Recheck the pi chain, in case we got a priority setting
 416  *
 417  * Called from sched_setscheduler
 418  */
 419 void __sched rt_mutex_adjust_pi(struct task_struct *task)
 420 {
 421         struct rt_mutex_waiter *waiter;
 422         struct rt_mutex_base *next_lock;
 423         unsigned long flags;
 424
 425         raw_spin_lock_irqsave(&task->pi_lock, flags);
 426
 427         waiter = task->pi_blocked_on;
 428         if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
 429                 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 430                 return;
 431         }
 432         next_lock = waiter->lock;
 433         raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 434
 435         /* gets dropped in rt_mutex_adjust_prio_chain()! */
 436         get_task_struct(task);
 437
 438         rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
 439                                    next_lock, NULL, task);
 440 }
 441
 442 /*
 443  * Performs the wakeup of the top-waiter and re-enables preemption.
 444  */
 445 void __sched rt_mutex_postunlock(struct rt_wake_q_head *wqh)
 446 {
 447         rt_mutex_wake_up_q(wqh);
 448 }
 449
 450 #ifdef CONFIG_DEBUG_RT_MUTEXES
 451 void rt_mutex_debug_task_free(struct task_struct *task)
 452 {
 453         DEBUG_LOCKS_WARN_ON(!RB_EMPTY_ROOT(&task->pi_waiters.rb_root));
 454         DEBUG_LOCKS_WARN_ON(task->pi_blocked_on);
 455 }
 456 #endif