// SPDX-License-Identifier: GPL-2.0

  /* kernel/rwsem.c: R/W semaphores, public implementation
   *
   * Written by David Howells (dhowells@redhat.com).
   * Derived from asm-i386/semaphore.h

   *
   * Writer lock-stealing by Alex Shi <alex.shi@intel.com>
   * and Michel Lespinasse <walken@google.com>
   *
   * Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
   * and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
   *

   * Rwsem count bit fields re-definition and rwsem rearchitecture by
   * Waiman Long <longman@redhat.com> and
   * Peter Zijlstra <peterz@infradead.org>.

   */
  
  #include <linux/types.h>
  #include <linux/kernel.h>

  #include <linux/sched.h>

  #include <linux/sched/rt.h>
  #include <linux/sched/task.h>

  #include <linux/sched/debug.h>

  #include <linux/sched/wake_q.h>
  #include <linux/sched/signal.h>

  #include <linux/sched/clock.h>

  #include <linux/export.h>

  #include <linux/rwsem.h>

  #include <linux/atomic.h>

  #ifndef CONFIG_PREEMPT_RT

  #include "lock_events.h"
  
  /*

   * The least significant 2 bits of the owner value has the following

   * meanings when set.

   *  - Bit 0: RWSEM_READER_OWNED - The rwsem is owned by readers

   *  - Bit 1: RWSEM_NONSPINNABLE - Cannot spin on a reader-owned lock

   *

   * When the rwsem is reader-owned and a spinning writer has timed out,
   * the nonspinnable bit will be set to disable optimistic spinning.

   * When a writer acquires a rwsem, it puts its task_struct pointer
   * into the owner field. It is cleared after an unlock.
   *
   * When a reader acquires a rwsem, it will also puts its task_struct

   * pointer into the owner field with the RWSEM_READER_OWNED bit set.
   * On unlock, the owner field will largely be left untouched. So
   * for a free or reader-owned rwsem, the owner value may contain
   * information about the last reader that acquires the rwsem.

   *
   * That information may be helpful in debugging cases where the system
   * seems to hang on a reader owned rwsem especially if only one reader
   * is involved. Ideally we would like to track all the readers that own
   * a rwsem, but the overhead is simply too big.

   *

   * A fast path reader optimistic lock stealing is supported when the rwsem
   * is previously owned by a writer and the following conditions are met:
   *  - OSQ is empty
   *  - rwsem is not currently writer owned
   *  - the handoff isn't set.

   */
  #define RWSEM_READER_OWNED	(1UL << 0)

  #define RWSEM_NONSPINNABLE	(1UL << 1)

  #define RWSEM_OWNER_FLAGS_MASK	(RWSEM_READER_OWNED | RWSEM_NONSPINNABLE)

  
  #ifdef CONFIG_DEBUG_RWSEMS
  # define DEBUG_RWSEMS_WARN_ON(c, sem)	do {			\
  	if (!debug_locks_silent &&				\

  	    WARN_ONCE(c, "DEBUG_RWSEMS_WARN_ON(%s): count = 0x%lx, magic = 0x%lx, owner = 0x%lx, curr 0x%lx, list %sempty
  ",\

  		#c, atomic_long_read(&(sem)->count),		\

  		(unsigned long) sem->magic,			\

  		atomic_long_read(&(sem)->owner), (long)current,	\

  		list_empty(&(sem)->wait_list) ? "" : "not "))	\
  			debug_locks_off();			\
  	} while (0)
  #else
  # define DEBUG_RWSEMS_WARN_ON(c, sem)
  #endif
  
  /*

   * On 64-bit architectures, the bit definitions of the count are:

   *

   * Bit  0    - writer locked bit
   * Bit  1    - waiters present bit
   * Bit  2    - lock handoff bit
   * Bits 3-7  - reserved
   * Bits 8-62 - 55-bit reader count
   * Bit  63   - read fail bit
   *
   * On 32-bit architectures, the bit definitions of the count are:
   *
   * Bit  0    - writer locked bit
   * Bit  1    - waiters present bit
   * Bit  2    - lock handoff bit
   * Bits 3-7  - reserved
   * Bits 8-30 - 23-bit reader count
   * Bit  31   - read fail bit
   *
   * It is not likely that the most significant bit (read fail bit) will ever
   * be set. This guard bit is still checked anyway in the down_read() fastpath
   * just in case we need to use up more of the reader bits for other purpose
   * in the future.

   *
   * atomic_long_fetch_add() is used to obtain reader lock, whereas
   * atomic_long_cmpxchg() will be used to obtain writer lock.

   *
   * There are three places where the lock handoff bit may be set or cleared.

   * 1) rwsem_mark_wake() for readers		-- set, clear
   * 2) rwsem_try_write_lock() for writers	-- set, clear
   * 3) rwsem_del_waiter()			-- clear

   *
   * For all the above cases, wait_lock will be held. A writer must also
   * be the first one in the wait_list to be eligible for setting the handoff
   * bit. So concurrent setting/clearing of handoff bit is not possible.

   */
  #define RWSEM_WRITER_LOCKED	(1UL << 0)
  #define RWSEM_FLAG_WAITERS	(1UL << 1)

  #define RWSEM_FLAG_HANDOFF	(1UL << 2)

  #define RWSEM_FLAG_READFAIL	(1UL << (BITS_PER_LONG - 1))

  #define RWSEM_READER_SHIFT	8
  #define RWSEM_READER_BIAS	(1UL << RWSEM_READER_SHIFT)
  #define RWSEM_READER_MASK	(~(RWSEM_READER_BIAS - 1))
  #define RWSEM_WRITER_MASK	RWSEM_WRITER_LOCKED
  #define RWSEM_LOCK_MASK		(RWSEM_WRITER_MASK|RWSEM_READER_MASK)

  #define RWSEM_READ_FAILED_MASK	(RWSEM_WRITER_MASK|RWSEM_FLAG_WAITERS|\

  				 RWSEM_FLAG_HANDOFF|RWSEM_FLAG_READFAIL)

  
  /*
   * All writes to owner are protected by WRITE_ONCE() to make sure that
   * store tearing can't happen as optimistic spinners may read and use
   * the owner value concurrently without lock. Read from owner, however,
   * may not need READ_ONCE() as long as the pointer value is only used
   * for comparison and isn't being dereferenced.
   */
  static inline void rwsem_set_owner(struct rw_semaphore *sem)
  {

  	atomic_long_set(&sem->owner, (long)current);

  }
  
  static inline void rwsem_clear_owner(struct rw_semaphore *sem)
  {

  	atomic_long_set(&sem->owner, 0);
  }
  
  /*
   * Test the flags in the owner field.
   */
  static inline bool rwsem_test_oflags(struct rw_semaphore *sem, long flags)
  {
  	return atomic_long_read(&sem->owner) & flags;

  }
  
  /*
   * The task_struct pointer of the last owning reader will be left in
   * the owner field.
   *
   * Note that the owner value just indicates the task has owned the rwsem
   * previously, it may not be the real owner or one of the real owners
   * anymore when that field is examined, so take it with a grain of salt.

   *
   * The reader non-spinnable bit is preserved.

   */
  static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
  					    struct task_struct *owner)
  {

  	unsigned long val = (unsigned long)owner | RWSEM_READER_OWNED |

  		(atomic_long_read(&sem->owner) & RWSEM_NONSPINNABLE);

  	atomic_long_set(&sem->owner, val);

  }
  
  static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
  {
  	__rwsem_set_reader_owned(sem, current);
  }
  
  /*

   * Return true if the rwsem is owned by a reader.

   */

  static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)

  {

  #ifdef CONFIG_DEBUG_RWSEMS
  	/*
  	 * Check the count to see if it is write-locked.
  	 */
  	long count = atomic_long_read(&sem->count);
  
  	if (count & RWSEM_WRITER_MASK)
  		return false;
  #endif
  	return rwsem_test_oflags(sem, RWSEM_READER_OWNED);

  }
  
  #ifdef CONFIG_DEBUG_RWSEMS
  /*
   * With CONFIG_DEBUG_RWSEMS configured, it will make sure that if there
   * is a task pointer in owner of a reader-owned rwsem, it will be the
   * real owner or one of the real owners. The only exception is when the
   * unlock is done by up_read_non_owner().
   */
  static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
  {

  	unsigned long val = atomic_long_read(&sem->owner);
  
  	while ((val & ~RWSEM_OWNER_FLAGS_MASK) == (unsigned long)current) {
  		if (atomic_long_try_cmpxchg(&sem->owner, &val,
  					    val & RWSEM_OWNER_FLAGS_MASK))
  			return;
  	}

  }
  #else
  static inline void rwsem_clear_reader_owned(struct rw_semaphore *sem)
  {
  }
  #endif
  
  /*

   * Set the RWSEM_NONSPINNABLE bits if the RWSEM_READER_OWNED flag
   * remains set. Otherwise, the operation will be aborted.
   */
  static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
  {
  	unsigned long owner = atomic_long_read(&sem->owner);
  
  	do {
  		if (!(owner & RWSEM_READER_OWNED))
  			break;
  		if (owner & RWSEM_NONSPINNABLE)
  			break;
  	} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
  					  owner | RWSEM_NONSPINNABLE));
  }

  static inline bool rwsem_read_trylock(struct rw_semaphore *sem, long *cntp)

  {

  	*cntp = atomic_long_add_return_acquire(RWSEM_READER_BIAS, &sem->count);

  	if (WARN_ON_ONCE(*cntp < 0))

  		rwsem_set_nonspinnable(sem);

  	if (!(*cntp & RWSEM_READ_FAILED_MASK)) {

  		rwsem_set_reader_owned(sem);
  		return true;
  	}
  
  	return false;

  }

  static inline bool rwsem_write_trylock(struct rw_semaphore *sem)
  {
  	long tmp = RWSEM_UNLOCKED_VALUE;
  
  	if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp, RWSEM_WRITER_LOCKED)) {
  		rwsem_set_owner(sem);
  		return true;
  	}
  
  	return false;
  }

  /*

   * Return just the real task structure pointer of the owner
   */
  static inline struct task_struct *rwsem_owner(struct rw_semaphore *sem)
  {
  	return (struct task_struct *)
  		(atomic_long_read(&sem->owner) & ~RWSEM_OWNER_FLAGS_MASK);
  }
  
  /*
   * Return the real task structure pointer of the owner and the embedded
   * flags in the owner. pflags must be non-NULL.
   */
  static inline struct task_struct *
  rwsem_owner_flags(struct rw_semaphore *sem, unsigned long *pflags)
  {
  	unsigned long owner = atomic_long_read(&sem->owner);
  
  	*pflags = owner & RWSEM_OWNER_FLAGS_MASK;
  	return (struct task_struct *)(owner & ~RWSEM_OWNER_FLAGS_MASK);
  }
  
  /*

   * Guide to the rw_semaphore's count field.
   *
   * When the RWSEM_WRITER_LOCKED bit in count is set, the lock is owned
   * by a writer.
   *
   * The lock is owned by readers when
   * (1) the RWSEM_WRITER_LOCKED isn't set in count,
   * (2) some of the reader bits are set in count, and
   * (3) the owner field has RWSEM_READ_OWNED bit set.
   *
   * Having some reader bits set is not enough to guarantee a readers owned
   * lock as the readers may be in the process of backing out from the count
   * and a writer has just released the lock. So another writer may steal
   * the lock immediately after that.
   */
  
  /*
   * Initialize an rwsem:
   */
  void __init_rwsem(struct rw_semaphore *sem, const char *name,
  		  struct lock_class_key *key)
  {
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  	/*
  	 * Make sure we are not reinitializing a held semaphore:
  	 */
  	debug_check_no_locks_freed((void *)sem, sizeof(*sem));

  	lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);

  #endif

  #ifdef CONFIG_DEBUG_RWSEMS
  	sem->magic = sem;
  #endif

  	atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE);
  	raw_spin_lock_init(&sem->wait_lock);
  	INIT_LIST_HEAD(&sem->wait_list);

  	atomic_long_set(&sem->owner, 0L);

  #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  	osq_lock_init(&sem->osq);
  #endif
  }

  EXPORT_SYMBOL(__init_rwsem);
  
  enum rwsem_waiter_type {
  	RWSEM_WAITING_FOR_WRITE,
  	RWSEM_WAITING_FOR_READ
  };
  
  struct rwsem_waiter {
  	struct list_head list;
  	struct task_struct *task;
  	enum rwsem_waiter_type type;

  	unsigned long timeout;

  	bool handoff_set;

  };

  #define rwsem_first_waiter(sem) \
  	list_first_entry(&sem->wait_list, struct rwsem_waiter, list)

  
  enum rwsem_wake_type {
  	RWSEM_WAKE_ANY,		/* Wake whatever's at head of wait list */
  	RWSEM_WAKE_READERS,	/* Wake readers only */
  	RWSEM_WAKE_READ_OWNED	/* Waker thread holds the read lock */
  };

  /*
   * The typical HZ value is either 250 or 1000. So set the minimum waiting
   * time to at least 4ms or 1 jiffy (if it is higher than 4ms) in the wait
   * queue before initiating the handoff protocol.
   */
  #define RWSEM_WAIT_TIMEOUT	DIV_ROUND_UP(HZ, 250)

  /*

   * Magic number to batch-wakeup waiting readers, even when writers are
   * also present in the queue. This both limits the amount of work the
   * waking thread must do and also prevents any potential counter overflow,
   * however unlikely.
   */
  #define MAX_READERS_WAKEUP	0x100

  static inline void
  rwsem_add_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
  {
  	lockdep_assert_held(&sem->wait_lock);
  	list_add_tail(&waiter->list, &sem->wait_list);
  	/* caller will set RWSEM_FLAG_WAITERS */
  }
  
  /*
   * Remove a waiter from the wait_list and clear flags.
   *
   * Both rwsem_mark_wake() and rwsem_try_write_lock() contain a full 'copy' of
   * this function. Modify with care.
   */
  static inline void
  rwsem_del_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter)
  {
  	lockdep_assert_held(&sem->wait_lock);
  	list_del(&waiter->list);
  	if (likely(!list_empty(&sem->wait_list)))
  		return;
  
  	atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
  }

  /*

   * handle the lock release when processes blocked on it that can now run
   * - if we come here from up_xxxx(), then the RWSEM_FLAG_WAITERS bit must
   *   have been set.
   * - there must be someone on the queue
   * - the wait_lock must be held by the caller
   * - tasks are marked for wakeup, the caller must later invoke wake_up_q()
   *   to actually wakeup the blocked task(s) and drop the reference count,
   *   preferably when the wait_lock is released
   * - woken process blocks are discarded from the list after having task zeroed
   * - writers are only marked woken if downgrading is false

   *
   * Implies rwsem_del_waiter() for all woken readers.

   */

  static void rwsem_mark_wake(struct rw_semaphore *sem,
  			    enum rwsem_wake_type wake_type,
  			    struct wake_q_head *wake_q)

  {
  	struct rwsem_waiter *waiter, *tmp;
  	long oldcount, woken = 0, adjustment = 0;
  	struct list_head wlist;

  	lockdep_assert_held(&sem->wait_lock);

  	/*
  	 * Take a peek at the queue head waiter such that we can determine
  	 * the wakeup(s) to perform.
  	 */

  	waiter = rwsem_first_waiter(sem);

  
  	if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
  		if (wake_type == RWSEM_WAKE_ANY) {
  			/*
  			 * Mark writer at the front of the queue for wakeup.
  			 * Until the task is actually later awoken later by
  			 * the caller, other writers are able to steal it.
  			 * Readers, on the other hand, will block as they
  			 * will notice the queued writer.
  			 */
  			wake_q_add(wake_q, waiter->task);
  			lockevent_inc(rwsem_wake_writer);
  		}
  
  		return;
  	}
  
  	/*

  	 * No reader wakeup if there are too many of them already.
  	 */
  	if (unlikely(atomic_long_read(&sem->count) < 0))
  		return;
  
  	/*

  	 * Writers might steal the lock before we grant it to the next reader.
  	 * We prefer to do the first reader grant before counting readers
  	 * so we can bail out early if a writer stole the lock.
  	 */
  	if (wake_type != RWSEM_WAKE_READ_OWNED) {

  		struct task_struct *owner;

  		adjustment = RWSEM_READER_BIAS;
  		oldcount = atomic_long_fetch_add(adjustment, &sem->count);
  		if (unlikely(oldcount & RWSEM_WRITER_MASK)) {

  			/*
  			 * When we've been waiting "too" long (for writers
  			 * to give up the lock), request a HANDOFF to
  			 * force the issue.
  			 */

  			if (time_after(jiffies, waiter->timeout)) {
  				if (!(oldcount & RWSEM_FLAG_HANDOFF)) {
  					adjustment -= RWSEM_FLAG_HANDOFF;
  					lockevent_inc(rwsem_rlock_handoff);
  				}
  				waiter->handoff_set = true;

  			}
  
  			atomic_long_add(-adjustment, &sem->count);

  			return;
  		}
  		/*
  		 * Set it to reader-owned to give spinners an early
  		 * indication that readers now have the lock.

  		 * The reader nonspinnable bit seen at slowpath entry of
  		 * the reader is copied over.

  		 */

  		owner = waiter->task;

  		__rwsem_set_reader_owned(sem, owner);

  	}
  
  	/*

  	 * Grant up to MAX_READERS_WAKEUP read locks to all the readers in the
  	 * queue. We know that the woken will be at least 1 as we accounted

  	 * for above. Note we increment the 'active part' of the count by the
  	 * number of readers before waking any processes up.
  	 *

  	 * This is an adaptation of the phase-fair R/W locks where at the
  	 * reader phase (first waiter is a reader), all readers are eligible
  	 * to acquire the lock at the same time irrespective of their order
  	 * in the queue. The writers acquire the lock according to their
  	 * order in the queue.
  	 *

  	 * We have to do wakeup in 2 passes to prevent the possibility that
  	 * the reader count may be decremented before it is incremented. It
  	 * is because the to-be-woken waiter may not have slept yet. So it
  	 * may see waiter->task got cleared, finish its critical section and
  	 * do an unlock before the reader count increment.
  	 *
  	 * 1) Collect the read-waiters in a separate list, count them and
  	 *    fully increment the reader count in rwsem.
  	 * 2) For each waiters in the new list, clear waiter->task and
  	 *    put them into wake_q to be woken up later.
  	 */

  	INIT_LIST_HEAD(&wlist);
  	list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) {

  		if (waiter->type == RWSEM_WAITING_FOR_WRITE)

  			continue;

  
  		woken++;

  		list_move_tail(&waiter->list, &wlist);
  
  		/*
  		 * Limit # of readers that can be woken up per wakeup call.
  		 */
  		if (woken >= MAX_READERS_WAKEUP)
  			break;

  	}

  
  	adjustment = woken * RWSEM_READER_BIAS - adjustment;
  	lockevent_cond_inc(rwsem_wake_reader, woken);

  
  	oldcount = atomic_long_read(&sem->count);

  	if (list_empty(&sem->wait_list)) {

  		/*
  		 * Combined with list_move_tail() above, this implies
  		 * rwsem_del_waiter().
  		 */

  		adjustment -= RWSEM_FLAG_WAITERS;

  		if (oldcount & RWSEM_FLAG_HANDOFF)
  			adjustment -= RWSEM_FLAG_HANDOFF;
  	} else if (woken) {
  		/*
  		 * When we've woken a reader, we no longer need to force
  		 * writers to give up the lock and we can clear HANDOFF.
  		 */
  		if (oldcount & RWSEM_FLAG_HANDOFF)
  			adjustment -= RWSEM_FLAG_HANDOFF;

  	}
  
  	if (adjustment)
  		atomic_long_add(adjustment, &sem->count);
  
  	/* 2nd pass */
  	list_for_each_entry_safe(waiter, tmp, &wlist, list) {
  		struct task_struct *tsk;
  
  		tsk = waiter->task;
  		get_task_struct(tsk);
  
  		/*
  		 * Ensure calling get_task_struct() before setting the reader

  		 * waiter to nil such that rwsem_down_read_slowpath() cannot

  		 * race with do_exit() by always holding a reference count
  		 * to the task to wakeup.
  		 */
  		smp_store_release(&waiter->task, NULL);
  		/*
  		 * Ensure issuing the wakeup (either by us or someone else)
  		 * after setting the reader waiter to nil.
  		 */
  		wake_q_add_safe(wake_q, tsk);
  	}
  }
  
  /*
   * This function must be called with the sem->wait_lock held to prevent
   * race conditions between checking the rwsem wait list and setting the
   * sem->count accordingly.

   *

   * Implies rwsem_del_waiter() on success.

   */

  static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,

  					struct rwsem_waiter *waiter)

  {

  	struct rwsem_waiter *first = rwsem_first_waiter(sem);

  	long count, new;

  	lockdep_assert_held(&sem->wait_lock);

  	count = atomic_long_read(&sem->count);

  	do {
  		bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF);

  		if (has_handoff) {

  			/*
  			 * Honor handoff bit and yield only when the first
  			 * waiter is the one that set it. Otherwisee, we
  			 * still try to acquire the rwsem.
  			 */
  			if (first->handoff_set && (waiter != first))

  				return false;

  			/*
  			 * First waiter can inherit a previously set handoff
  			 * bit and spin on rwsem if lock acquisition fails.
  			 */
  			if (waiter == first)
  				waiter->handoff_set = true;

  		}

  		new = count;
  
  		if (count & RWSEM_LOCK_MASK) {

  			if (has_handoff || (!rt_task(waiter->task) &&
  					    !time_after(jiffies, waiter->timeout)))

  				return false;
  
  			new |= RWSEM_FLAG_HANDOFF;
  		} else {
  			new |= RWSEM_WRITER_LOCKED;
  			new &= ~RWSEM_FLAG_HANDOFF;
  
  			if (list_is_singular(&sem->wait_list))
  				new &= ~RWSEM_FLAG_WAITERS;
  		}
  	} while (!atomic_long_try_cmpxchg_acquire(&sem->count, &count, new));
  
  	/*
  	 * We have either acquired the lock with handoff bit cleared or
  	 * set the handoff bit.
  	 */

  	if (new & RWSEM_FLAG_HANDOFF) {
  		waiter->handoff_set = true;
  		lockevent_inc(rwsem_wlock_handoff);

  		return false;

  	}

  	/*
  	 * Have rwsem_try_write_lock() fully imply rwsem_del_waiter() on
  	 * success.
  	 */
  	list_del(&waiter->list);

  	rwsem_set_owner(sem);
  	return true;

  }

  /*
   * The rwsem_spin_on_owner() function returns the following 4 values
   * depending on the lock owner state.
   *   OWNER_NULL  : owner is currently NULL
   *   OWNER_WRITER: when owner changes and is a writer
   *   OWNER_READER: when owner changes and the new owner may be a reader.
   *   OWNER_NONSPINNABLE:
   *		   when optimistic spinning has to stop because either the
   *		   owner stops running, is unknown, or its timeslice has
   *		   been used up.
   */
  enum owner_state {
  	OWNER_NULL		= 1 << 0,
  	OWNER_WRITER		= 1 << 1,
  	OWNER_READER		= 1 << 2,
  	OWNER_NONSPINNABLE	= 1 << 3,
  };

  #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  /*
   * Try to acquire write lock before the writer has been put on wait queue.
   */
  static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
  {
  	long count = atomic_long_read(&sem->count);

  	while (!(count & (RWSEM_LOCK_MASK|RWSEM_FLAG_HANDOFF))) {

  		if (atomic_long_try_cmpxchg_acquire(&sem->count, &count,

  					count | RWSEM_WRITER_LOCKED)) {

  			rwsem_set_owner(sem);

  			lockevent_inc(rwsem_opt_lock);

  			return true;
  		}
  	}
  	return false;
  }
  
  static inline bool owner_on_cpu(struct task_struct *owner)
  {
  	/*
  	 * As lock holder preemption issue, we both skip spinning if
  	 * task is not on cpu or its cpu is preempted
  	 */
  	return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
  }

  static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)

  {
  	struct task_struct *owner;

  	unsigned long flags;

  	bool ret = true;

  	if (need_resched()) {
  		lockevent_inc(rwsem_opt_fail);

  		return false;

  	}

  	preempt_disable();

  	rcu_read_lock();

  	owner = rwsem_owner_flags(sem, &flags);

  	/*
  	 * Don't check the read-owner as the entry may be stale.
  	 */

  	if ((flags & RWSEM_NONSPINNABLE) ||

  	    (owner && !(flags & RWSEM_READER_OWNED) && !owner_on_cpu(owner)))

  		ret = false;

  	rcu_read_unlock();

  	preempt_enable();
  
  	lockevent_cond_inc(rwsem_opt_fail, !ret);

  	return ret;
  }

  #define OWNER_SPINNABLE		(OWNER_NULL | OWNER_WRITER | OWNER_READER)

  static inline enum owner_state

  rwsem_owner_state(struct task_struct *owner, unsigned long flags)

  {

  	if (flags & RWSEM_NONSPINNABLE)

  		return OWNER_NONSPINNABLE;

  	if (flags & RWSEM_READER_OWNED)

  		return OWNER_READER;

  	return owner ? OWNER_WRITER : OWNER_NULL;

  }

  static noinline enum owner_state

  rwsem_spin_on_owner(struct rw_semaphore *sem)

  {

  	struct task_struct *new, *owner;
  	unsigned long flags, new_flags;
  	enum owner_state state;

  	owner = rwsem_owner_flags(sem, &flags);

  	state = rwsem_owner_state(owner, flags);

  	if (state != OWNER_WRITER)
  		return state;

  
  	rcu_read_lock();

  	for (;;) {

  		/*
  		 * When a waiting writer set the handoff flag, it may spin
  		 * on the owner as well. Once that writer acquires the lock,
  		 * we can spin on it. So we don't need to quit even when the
  		 * handoff bit is set.
  		 */

  		new = rwsem_owner_flags(sem, &new_flags);
  		if ((new != owner) || (new_flags != flags)) {

  			state = rwsem_owner_state(new, new_flags);

  			break;
  		}

  		/*
  		 * Ensure we emit the owner->on_cpu, dereference _after_
  		 * checking sem->owner still matches owner, if that fails,
  		 * owner might point to free()d memory, if it still matches,
  		 * the rcu_read_lock() ensures the memory stays valid.
  		 */
  		barrier();

  		if (need_resched() || !owner_on_cpu(owner)) {

  			state = OWNER_NONSPINNABLE;
  			break;

  		}
  
  		cpu_relax();
  	}
  	rcu_read_unlock();

  	return state;

  }

  /*
   * Calculate reader-owned rwsem spinning threshold for writer
   *
   * The more readers own the rwsem, the longer it will take for them to
   * wind down and free the rwsem. So the empirical formula used to
   * determine the actual spinning time limit here is:
   *
   *   Spinning threshold = (10 + nr_readers/2)us
   *
   * The limit is capped to a maximum of 25us (30 readers). This is just
   * a heuristic and is subjected to change in the future.
   */
  static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
  {
  	long count = atomic_long_read(&sem->count);
  	int readers = count >> RWSEM_READER_SHIFT;
  	u64 delta;
  
  	if (readers > 30)
  		readers = 30;
  	delta = (20 + readers) * NSEC_PER_USEC / 2;
  
  	return sched_clock() + delta;
  }

  static bool rwsem_optimistic_spin(struct rw_semaphore *sem)

  {
  	bool taken = false;

  	int prev_owner_state = OWNER_NULL;

  	int loop = 0;
  	u64 rspin_threshold = 0;

  
  	preempt_disable();
  
  	/* sem->wait_lock should not be held when doing optimistic spinning */

  	if (!osq_lock(&sem->osq))
  		goto done;
  
  	/*
  	 * Optimistically spin on the owner field and attempt to acquire the
  	 * lock whenever the owner changes. Spinning will be stopped when:
  	 *  1) the owning writer isn't running; or

  	 *  2) readers own the lock and spinning time has exceeded limit.

  	 */

  	for (;;) {

  		enum owner_state owner_state;

  		owner_state = rwsem_spin_on_owner(sem);

  		if (!(owner_state & OWNER_SPINNABLE))
  			break;

  		/*
  		 * Try to acquire the lock
  		 */

  		taken = rwsem_try_write_lock_unqueued(sem);

  
  		if (taken)

  			break;

  
  		/*

  		 * Time-based reader-owned rwsem optimistic spinning
  		 */

  		if (owner_state == OWNER_READER) {

  			/*
  			 * Re-initialize rspin_threshold every time when
  			 * the owner state changes from non-reader to reader.
  			 * This allows a writer to steal the lock in between
  			 * 2 reader phases and have the threshold reset at
  			 * the beginning of the 2nd reader phase.
  			 */
  			if (prev_owner_state != OWNER_READER) {

  				if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))

  					break;
  				rspin_threshold = rwsem_rspin_threshold(sem);
  				loop = 0;
  			}
  
  			/*
  			 * Check time threshold once every 16 iterations to
  			 * avoid calling sched_clock() too frequently so
  			 * as to reduce the average latency between the times
  			 * when the lock becomes free and when the spinner
  			 * is ready to do a trylock.
  			 */
  			else if (!(++loop & 0xf) && (sched_clock() > rspin_threshold)) {
  				rwsem_set_nonspinnable(sem);
  				lockevent_inc(rwsem_opt_nospin);
  				break;
  			}
  		}
  
  		/*

  		 * An RT task cannot do optimistic spinning if it cannot
  		 * be sure the lock holder is running or live-lock may
  		 * happen if the current task and the lock holder happen
  		 * to run in the same CPU. However, aborting optimistic
  		 * spinning while a NULL owner is detected may miss some
  		 * opportunity where spinning can continue without causing
  		 * problem.
  		 *
  		 * There are 2 possible cases where an RT task may be able
  		 * to continue spinning.
  		 *
  		 * 1) The lock owner is in the process of releasing the
  		 *    lock, sem->owner is cleared but the lock has not
  		 *    been released yet.
  		 * 2) The lock was free and owner cleared, but another
  		 *    task just comes in and acquire the lock before
  		 *    we try to get it. The new owner may be a spinnable
  		 *    writer.
  		 *

  		 * To take advantage of two scenarios listed above, the RT

  		 * task is made to retry one more time to see if it can
  		 * acquire the lock or continue spinning on the new owning
  		 * writer. Of course, if the time lag is long enough or the
  		 * new owner is not a writer or spinnable, the RT task will
  		 * quit spinning.
  		 *
  		 * If the owner is a writer, the need_resched() check is
  		 * done inside rwsem_spin_on_owner(). If the owner is not
  		 * a writer, need_resched() check needs to be done here.

  		 */

  		if (owner_state != OWNER_WRITER) {
  			if (need_resched())
  				break;
  			if (rt_task(current) &&
  			   (prev_owner_state != OWNER_WRITER))
  				break;
  		}
  		prev_owner_state = owner_state;

  
  		/*
  		 * The cpu_relax() call is a compiler barrier which forces
  		 * everything in this loop to be re-loaded. We don't need
  		 * memory barriers as we'll eventually observe the right
  		 * values at the cost of a few extra spins.
  		 */
  		cpu_relax();
  	}
  	osq_unlock(&sem->osq);
  done:
  	preempt_enable();
  	lockevent_cond_inc(rwsem_opt_fail, !taken);
  	return taken;
  }

  
  /*

   * Clear the owner's RWSEM_NONSPINNABLE bit if it is set. This should

   * only be called when the reader count reaches 0.

   */

  static inline void clear_nonspinnable(struct rw_semaphore *sem)

  {

  	if (rwsem_test_oflags(sem, RWSEM_NONSPINNABLE))
  		atomic_long_andnot(RWSEM_NONSPINNABLE, &sem->owner);

  }

  #else

  static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)

  {
  	return false;
  }

  static inline bool rwsem_optimistic_spin(struct rw_semaphore *sem)

  {
  	return false;
  }

  static inline void clear_nonspinnable(struct rw_semaphore *sem) { }

  static inline enum owner_state

  rwsem_spin_on_owner(struct rw_semaphore *sem)

  {

  	return OWNER_NONSPINNABLE;

  }

  #endif
  
  /*
   * Wait for the read lock to be granted
   */

  static struct rw_semaphore __sched *

  rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int state)

  {

  	long adjustment = -RWSEM_READER_BIAS;

  	long rcnt = (count >> RWSEM_READER_SHIFT);

  	struct rwsem_waiter waiter;
  	DEFINE_WAKE_Q(wake_q);

  	bool wake = false;

  	/*

  	 * To prevent a constant stream of readers from starving a sleeping

  	 * waiter, don't attempt optimistic lock stealing if the lock is
  	 * currently owned by readers.

  	 */

  	if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) &&
  	    (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED))

  		goto queue;
  
  	/*

  	 * Reader optimistic lock stealing.

  	 */

  	if (!(count & (RWSEM_WRITER_LOCKED | RWSEM_FLAG_HANDOFF))) {

  		rwsem_set_reader_owned(sem);
  		lockevent_inc(rwsem_rlock_steal);

  		/*

  		 * Wake up other readers in the wait queue if it is
  		 * the first reader.

  		 */

  		if ((rcnt == 1) && (count & RWSEM_FLAG_WAITERS)) {

  			raw_spin_lock_irq(&sem->wait_lock);
  			if (!list_empty(&sem->wait_list))
  				rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED,
  						&wake_q);
  			raw_spin_unlock_irq(&sem->wait_lock);
  			wake_up_q(&wake_q);
  		}
  		return sem;
  	}
  
  queue:

  	waiter.task = current;
  	waiter.type = RWSEM_WAITING_FOR_READ;

  	waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;

  	waiter.handoff_set = false;

  
  	raw_spin_lock_irq(&sem->wait_lock);
  	if (list_empty(&sem->wait_list)) {
  		/*
  		 * In case the wait queue is empty and the lock isn't owned

  		 * by a writer or has the handoff bit set, this reader can
  		 * exit the slowpath and return immediately as its
  		 * RWSEM_READER_BIAS has already been set in the count.

  		 */

  		if (!(atomic_long_read(&sem->count) &

  		     (RWSEM_WRITER_MASK | RWSEM_FLAG_HANDOFF))) {

  			/* Provide lock ACQUIRE */
  			smp_acquire__after_ctrl_dep();

  			raw_spin_unlock_irq(&sem->wait_lock);
  			rwsem_set_reader_owned(sem);
  			lockevent_inc(rwsem_rlock_fast);
  			return sem;
  		}
  		adjustment += RWSEM_FLAG_WAITERS;
  	}

  	rwsem_add_waiter(sem, &waiter);

  
  	/* we're now waiting on the lock, but no longer actively locking */

  	count = atomic_long_add_return(adjustment, &sem->count);

  
  	/*
  	 * If there are no active locks, wake the front queued process(es).
  	 *
  	 * If there are no writers and we are first in the queue,
  	 * wake our own waiter to join the existing active readers !
  	 */

  	if (!(count & RWSEM_LOCK_MASK)) {

  		clear_nonspinnable(sem);

  		wake = true;
  	}
  	if (wake || (!(count & RWSEM_WRITER_MASK) &&
  		    (adjustment & RWSEM_FLAG_WAITERS)))

  		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);

  
  	raw_spin_unlock_irq(&sem->wait_lock);
  	wake_up_q(&wake_q);
  
  	/* wait to be given the lock */

  	for (;;) {

  		set_current_state(state);

  		if (!smp_load_acquire(&waiter.task)) {

  			/* Matches rwsem_mark_wake()'s smp_store_release(). */

  			break;

  		}

  		if (signal_pending_state(state, current)) {
  			raw_spin_lock_irq(&sem->wait_lock);
  			if (waiter.task)
  				goto out_nolock;
  			raw_spin_unlock_irq(&sem->wait_lock);

  			/* Ordered by sem->wait_lock against rwsem_mark_wake(). */

  			break;
  		}
  		schedule();
  		lockevent_inc(rwsem_sleep_reader);
  	}
  
  	__set_current_state(TASK_RUNNING);
  	lockevent_inc(rwsem_rlock);
  	return sem;

  out_nolock:

  	rwsem_del_waiter(sem, &waiter);

  	raw_spin_unlock_irq(&sem->wait_lock);
  	__set_current_state(TASK_RUNNING);
  	lockevent_inc(rwsem_rlock_fail);
  	return ERR_PTR(-EINTR);
  }

  /*
   * Wait until we successfully acquire the write lock
   */

  static struct rw_semaphore *
  rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)

  {
  	long count;

  	struct rwsem_waiter waiter;

  	DEFINE_WAKE_Q(wake_q);
  
  	/* do optimistic spinning and steal lock if possible */

  	if (rwsem_can_spin_on_owner(sem) && rwsem_optimistic_spin(sem)) {

  		/* rwsem_optimistic_spin() implies ACQUIRE on success */

  		return sem;

  	}

  
  	/*
  	 * Optimistic spinning failed, proceed to the slowpath
  	 * and block until we can acquire the sem.
  	 */
  	waiter.task = current;
  	waiter.type = RWSEM_WAITING_FOR_WRITE;

  	waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;

  	waiter.handoff_set = false;

  
  	raw_spin_lock_irq(&sem->wait_lock);

  	rwsem_add_waiter(sem, &waiter);

  
  	/* we're now waiting on the lock */

  	if (rwsem_first_waiter(sem) != &waiter) {

  		count = atomic_long_read(&sem->count);
  
  		/*

  		 * If there were already threads queued before us and:

  		 *  1) there are no active locks, wake the front

  		 *     queued process(es) as the handoff bit might be set.
  		 *  2) there are no active writers and some readers, the lock
  		 *     must be read owned; so we try to wake any read lock
  		 *     waiters that were queued ahead of us.

  		 */

  		if (count & RWSEM_WRITER_MASK)
  			goto wait;

  		rwsem_mark_wake(sem, (count & RWSEM_READER_MASK)
  					? RWSEM_WAKE_READERS
  					: RWSEM_WAKE_ANY, &wake_q);

  		if (!wake_q_empty(&wake_q)) {
  			/*
  			 * We want to minimize wait_lock hold time especially
  			 * when a large number of readers are to be woken up.
  			 */
  			raw_spin_unlock_irq(&sem->wait_lock);
  			wake_up_q(&wake_q);
  			wake_q_init(&wake_q);	/* Used again, reinit */
  			raw_spin_lock_irq(&sem->wait_lock);
  		}

  	} else {

  		atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);

  	}

  wait:

  	/* wait until we successfully acquire the lock */
  	set_current_state(state);

  	for (;;) {

  		if (rwsem_try_write_lock(sem, &waiter)) {

  			/* rwsem_try_write_lock() implies ACQUIRE on success */

  			break;

  		}

  		raw_spin_unlock_irq(&sem->wait_lock);

  		if (signal_pending_state(state, current))
  			goto out_nolock;

  		/*
  		 * After setting the handoff bit and failing to acquire
  		 * the lock, attempt to spin on owner to accelerate lock
  		 * transfer. If the previous owner is a on-cpu writer and it
  		 * has just released the lock, OWNER_NULL will be returned.
  		 * In this case, we attempt to acquire the lock again
  		 * without sleeping.
  		 */

  		if (waiter.handoff_set) {

  			enum owner_state owner_state;
  
  			preempt_disable();
  			owner_state = rwsem_spin_on_owner(sem);
  			preempt_enable();
  
  			if (owner_state == OWNER_NULL)
  				goto trylock_again;
  		}

  		schedule();
  		lockevent_inc(rwsem_sleep_writer);
  		set_current_state(state);

  trylock_again:

  		raw_spin_lock_irq(&sem->wait_lock);
  	}
  	__set_current_state(TASK_RUNNING);

  	raw_spin_unlock_irq(&sem->wait_lock);
  	lockevent_inc(rwsem_wlock);

  	return sem;

  
  out_nolock:
  	__set_current_state(TASK_RUNNING);
  	raw_spin_lock_irq(&sem->wait_lock);

  	rwsem_del_waiter(sem, &waiter);
  	if (!list_empty(&sem->wait_list))

  		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);

  	raw_spin_unlock_irq(&sem->wait_lock);
  	wake_up_q(&wake_q);
  	lockevent_inc(rwsem_wlock_fail);

  	return ERR_PTR(-EINTR);
  }

  /*
   * handle waking up a waiter on the semaphore
   * - up_read/up_write has decremented the active part of count if we come here
   */

  static struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)

  {
  	unsigned long flags;
  	DEFINE_WAKE_Q(wake_q);
  
  	raw_spin_lock_irqsave(&sem->wait_lock, flags);
  
  	if (!list_empty(&sem->wait_list))

  		rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q);

  
  	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
  	wake_up_q(&wake_q);
  
  	return sem;
  }

  
  /*
   * downgrade a write lock into a read lock
   * - caller incremented waiting part of count and discovered it still negative
   * - just wake up any readers at the front of the queue
   */

  static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)

  {
  	unsigned long flags;
  	DEFINE_WAKE_Q(wake_q);
  
  	raw_spin_lock_irqsave(&sem->wait_lock, flags);
  
  	if (!list_empty(&sem->wait_list))

  		rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q);

  
  	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
  	wake_up_q(&wake_q);
  
  	return sem;
  }

  
  /*
   * lock for reading
   */

  static inline int __down_read_common(struct rw_semaphore *sem, int state)

  {

  	long count;
  
  	if (!rwsem_read_trylock(sem, &count)) {
  		if (IS_ERR(rwsem_down_read_slowpath(sem, count, state)))

  			return -EINTR;

  		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);

  	}

  	return 0;
  }
  
  static inline void __down_read(struct rw_semaphore *sem)
  {
  	__down_read_common(sem, TASK_UNINTERRUPTIBLE);

  }

  static inline int __down_read_interruptible(struct rw_semaphore *sem)
  {

  	return __down_read_common(sem, TASK_INTERRUPTIBLE);

  }

  static inline int __down_read_killable(struct rw_semaphore *sem)
  {

  	return __down_read_common(sem, TASK_KILLABLE);

  }
  
  static inline int __down_read_trylock(struct rw_semaphore *sem)
  {

  	long tmp;
  
  	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);

  	/*
  	 * Optimize for the case when the rwsem is not locked at all.
  	 */

  	tmp = RWSEM_UNLOCKED_VALUE;

  	do {
  		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
  					tmp + RWSEM_READER_BIAS)) {
  			rwsem_set_reader_owned(sem);
  			return 1;
  		}
  	} while (!(tmp & RWSEM_READ_FAILED_MASK));
  	return 0;
  }
  
  /*
   * lock for writing
   */

  static inline int __down_write_common(struct rw_semaphore *sem, int state)

  {

  	if (unlikely(!rwsem_write_trylock(sem))) {

  		if (IS_ERR(rwsem_down_write_slowpath(sem, state)))

  			return -EINTR;

  	}

  	return 0;
  }

  static inline void __down_write(struct rw_semaphore *sem)
  {
  	__down_write_common(sem, TASK_UNINTERRUPTIBLE);
  }
  
  static inline int __down_write_killable(struct rw_semaphore *sem)
  {
  	return __down_write_common(sem, TASK_KILLABLE);
  }

  static inline int __down_write_trylock(struct rw_semaphore *sem)
  {

  	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);

  	return rwsem_write_trylock(sem);

  }
  
  /*
   * unlock after reading
   */

  static inline void __up_read(struct rw_semaphore *sem)

  {
  	long tmp;

  	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);

  	DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);

  	rwsem_clear_reader_owned(sem);
  	tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count);

  	DEBUG_RWSEMS_WARN_ON(tmp < 0, sem);

  	if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) ==

  		      RWSEM_FLAG_WAITERS)) {

  		clear_nonspinnable(sem);

  		rwsem_wake(sem);

  	}

  }
  
  /*
   * unlock after writing
   */

  static inline void __up_write(struct rw_semaphore *sem)

  {

  	long tmp;

  	DEBUG_RWSEMS_WARN_ON(sem->magic != sem, sem);

  	/*
  	 * sem->owner may differ from current if the ownership is transferred
  	 * to an anonymous writer by setting the RWSEM_NONSPINNABLE bits.
  	 */

  	DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) &&
  			    !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE), sem);

  	rwsem_clear_owner(sem);

  	tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count);
  	if (unlikely(tmp & RWSEM_FLAG_WAITERS))

  		rwsem_wake(sem);

  }
  
  /*
   * downgrade write lock to read lock
   */
  static inline void __downgrade_write(struct rw_semaphore *sem)
  {
  	long tmp;
  
  	/*
  	 * When downgrading from exclusive to shared ownership,
  	 * anything inside the write-locked region cannot leak
  	 * into the read side. In contrast, anything in the
  	 * read-locked region is ok to be re-ordered into the
  	 * write side. As such, rely on RELEASE semantics.
  	 */

  	DEBUG_RWSEMS_WARN_ON(rwsem_owner(sem) != current, sem);

  	tmp = atomic_long_fetch_add_release(
  		-RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count);
  	rwsem_set_reader_owned(sem);
  	if (tmp & RWSEM_FLAG_WAITERS)
  		rwsem_downgrade_wake(sem);
  }

  #else /* !CONFIG_PREEMPT_RT */

  #define RT_MUTEX_BUILD_MUTEX

  #include "rtmutex.c"
  
  #define rwbase_set_and_save_current_state(state)	\
  	set_current_state(state)
  
  #define rwbase_restore_current_state()			\
  	__set_current_state(TASK_RUNNING)
  
  #define rwbase_rtmutex_lock_state(rtm, state)		\
  	__rt_mutex_lock(rtm, state)
  
  #define rwbase_rtmutex_slowlock_locked(rtm, state)	\

  	__rt_mutex_slowlock_locked(rtm, NULL, state)

  
  #define rwbase_rtmutex_unlock(rtm)			\
  	__rt_mutex_unlock(rtm)
  
  #define rwbase_rtmutex_trylock(rtm)			\
  	__rt_mutex_trylock(rtm)
  
  #define rwbase_signal_pending_state(state, current)	\
  	signal_pending_state(state, current)
  
  #define rwbase_schedule()				\
  	schedule()
  
  #include "rwbase_rt.c"

  void __init_rwsem(struct rw_semaphore *sem, const char *name,

  		  struct lock_class_key *key)
  {

  	init_rwbase_rt(&(sem)->rwbase);
  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC

  	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
  	lockdep_init_map_wait(&sem->dep_map, name, key, 0, LD_WAIT_SLEEP);

  #endif

  }
  EXPORT_SYMBOL(__init_rwsem);

  
  static inline void __down_read(struct rw_semaphore *sem)
  {
  	rwbase_read_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
  }
  
  static inline int __down_read_interruptible(struct rw_semaphore *sem)
  {
  	return rwbase_read_lock(&sem->rwbase, TASK_INTERRUPTIBLE);
  }
  
  static inline int __down_read_killable(struct rw_semaphore *sem)
  {
  	return rwbase_read_lock(&sem->rwbase, TASK_KILLABLE);
  }
  
  static inline int __down_read_trylock(struct rw_semaphore *sem)
  {
  	return rwbase_read_trylock(&sem->rwbase);
  }
  
  static inline void __up_read(struct rw_semaphore *sem)
  {
  	rwbase_read_unlock(&sem->rwbase, TASK_NORMAL);
  }
  
  static inline void __sched __down_write(struct rw_semaphore *sem)
  {
  	rwbase_write_lock(&sem->rwbase, TASK_UNINTERRUPTIBLE);
  }
  
  static inline int __sched __down_write_killable(struct rw_semaphore *sem)
  {
  	return rwbase_write_lock(&sem->rwbase, TASK_KILLABLE);
  }
  
  static inline int __down_write_trylock(struct rw_semaphore *sem)
  {
  	return rwbase_write_trylock(&sem->rwbase);
  }
  
  static inline void __up_write(struct rw_semaphore *sem)
  {
  	rwbase_write_unlock(&sem->rwbase);
  }
  
  static inline void __downgrade_write(struct rw_semaphore *sem)
  {
  	rwbase_write_downgrade(&sem->rwbase);
  }
  
  /* Debug stubs for the common API */
  #define DEBUG_RWSEMS_WARN_ON(c, sem)
  
  static inline void __rwsem_set_reader_owned(struct rw_semaphore *sem,
  					    struct task_struct *owner)
  {
  }
  
  static inline bool is_rwsem_reader_owned(struct rw_semaphore *sem)
  {
  	int count = atomic_read(&sem->rwbase.readers);
  
  	return count < 0 && count != READER_BIAS;
  }
  
  #endif /* CONFIG_PREEMPT_RT */

  /*
   * lock for reading
   */

  void __sched down_read(struct rw_semaphore *sem)

  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);

  }

  EXPORT_SYMBOL(down_read);

  int __sched down_read_interruptible(struct rw_semaphore *sem)
  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
  
  	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
  		rwsem_release(&sem->dep_map, _RET_IP_);
  		return -EINTR;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(down_read_interruptible);

  int __sched down_read_killable(struct rw_semaphore *sem)
  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
  
  	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {

  		rwsem_release(&sem->dep_map, _RET_IP_);

  		return -EINTR;
  	}

  	return 0;
  }

  EXPORT_SYMBOL(down_read_killable);

  /*
   * trylock for reading -- returns 1 if successful, 0 if contention
   */
  int down_read_trylock(struct rw_semaphore *sem)
  {
  	int ret = __down_read_trylock(sem);

  	if (ret == 1)

  		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  	return ret;
  }

  EXPORT_SYMBOL(down_read_trylock);
  
  /*
   * lock for writing
   */

  void __sched down_write(struct rw_semaphore *sem)

  {
  	might_sleep();
  	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);

  }

  EXPORT_SYMBOL(down_write);
  
  /*

   * lock for writing
   */
  int __sched down_write_killable(struct rw_semaphore *sem)
  {
  	might_sleep();
  	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);

  	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
  				  __down_write_killable)) {

  		rwsem_release(&sem->dep_map, _RET_IP_);

  		return -EINTR;
  	}

  	return 0;
  }

  EXPORT_SYMBOL(down_write_killable);
  
  /*

   * trylock for writing -- returns 1 if successful, 0 if contention
   */
  int down_write_trylock(struct rw_semaphore *sem)
  {
  	int ret = __down_write_trylock(sem);

  	if (ret == 1)

  		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);

  	return ret;
  }

  EXPORT_SYMBOL(down_write_trylock);
  
  /*
   * release a read lock
   */
  void up_read(struct rw_semaphore *sem)
  {

  	rwsem_release(&sem->dep_map, _RET_IP_);

  	__up_read(sem);
  }

  EXPORT_SYMBOL(up_read);
  
  /*
   * release a write lock
   */
  void up_write(struct rw_semaphore *sem)
  {

  	rwsem_release(&sem->dep_map, _RET_IP_);

  	__up_write(sem);
  }

  EXPORT_SYMBOL(up_write);
  
  /*
   * downgrade write lock to read lock
   */
  void downgrade_write(struct rw_semaphore *sem)
  {

  	lock_downgrade(&sem->dep_map, _RET_IP_);

  	__downgrade_write(sem);
  }

  EXPORT_SYMBOL(downgrade_write);

  
  #ifdef CONFIG_DEBUG_LOCK_ALLOC
  
  void down_read_nested(struct rw_semaphore *sem, int subclass)
  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);

  }

  EXPORT_SYMBOL(down_read_nested);

  int down_read_killable_nested(struct rw_semaphore *sem, int subclass)
  {
  	might_sleep();
  	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
  
  	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_killable)) {
  		rwsem_release(&sem->dep_map, _RET_IP_);
  		return -EINTR;
  	}
  
  	return 0;
  }
  EXPORT_SYMBOL(down_read_killable_nested);

  void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
  {
  	might_sleep();
  	rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
  }

  EXPORT_SYMBOL(_down_write_nest_lock);

  void down_read_non_owner(struct rw_semaphore *sem)
  {
  	might_sleep();

  	__down_read(sem);

  	__rwsem_set_reader_owned(sem, NULL);

  }

  EXPORT_SYMBOL(down_read_non_owner);

  void down_write_nested(struct rw_semaphore *sem, int subclass)
  {
  	might_sleep();
  	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

  	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);

  }

  EXPORT_SYMBOL(down_write_nested);

  int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
  {
  	might_sleep();
  	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

  	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock,
  				  __down_write_killable)) {

  		rwsem_release(&sem->dep_map, _RET_IP_);

  		return -EINTR;
  	}

  	return 0;
  }

  EXPORT_SYMBOL(down_write_killable_nested);

  void up_read_non_owner(struct rw_semaphore *sem)
  {

  	DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);

  	__up_read(sem);
  }

  EXPORT_SYMBOL(up_read_non_owner);

  #endif