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 // 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>
 #include <trace/events/lock.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:
  *  - 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\n",\
         #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.
  *
  * Return: true if wait_list isn't empty and false otherwise
  */
 static inline bool
 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 true;
 
     atomic_long_andnot(RWSEM_FLAG_HANDOFF | RWSEM_FLAG_WAITERS, &sem->count);
     return false;
 }
 
 /*
  * 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 (unlikely(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);
     }
 }
 
 /*
  * Remove a waiter and try to wake up other waiters in the wait queue
  * This function is called from the out_nolock path of both the reader and
  * writer slowpaths with wait_lock held. It releases the wait_lock and
  * optionally wake up waiters before it returns.
  */
 static inline void
 rwsem_del_wake_waiter(struct rw_semaphore *sem, struct rwsem_waiter *waiter,
               struct wake_q_head *wake_q)
               __releases(&sem->wait_lock)
 {
     bool first = rwsem_first_waiter(sem) == waiter;
 
     wake_q_init(wake_q);
 
     /*
      * If the wait_list isn't empty and the waiter to be deleted is
      * the first waiter, we wake up the remaining waiters as they may
      * be eligible to acquire or spin on the lock.
      */
     if (rwsem_del_waiter(sem, waiter) && first)
         rwsem_mark_wake(sem, RWSEM_WAKE_ANY, wake_q);
     raw_spin_unlock_irq(&sem->wait_lock);
     if (!wake_q_empty(wake_q))
         wake_up_q(wake_q);
 }
 
 /*
  * 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 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();
     /*
      * Disable preemption is equal to the RCU read-side crital section,
      * thus the task_strcut structure won't go away.
      */
     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;
     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;
 
     lockdep_assert_preemption_disabled();
 
     owner = rwsem_owner_flags(sem, &flags);
     state = rwsem_owner_state(owner, flags);
     if (state != OWNER_WRITER)
         return state;
 
     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,
          * our spinning context already disabled preemption which is
          * equal to RCU read-side crital section ensures the memory
          * stays valid.
          */
         barrier();
 
         if (need_resched() || !owner_on_cpu(owner)) {
             state = OWNER_NONSPINNABLE;
             break;
         }
 
         cpu_relax();
     }
 
     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 (unlikely(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
 
 /*
  * Prepare to wake up waiter(s) in the wait queue by putting them into the
  * given wake_q if the rwsem lock owner isn't a writer. If rwsem is likely
  * reader-owned, wake up read lock waiters in queue front or wake up any
  * front waiter otherwise.
 
  * This is being called from both reader and writer slow paths.
  */
 static inline void rwsem_cond_wake_waiter(struct rw_semaphore *sem, long count,
                       struct wake_q_head *wake_q)
 {
     enum rwsem_wake_type wake_type;
 
     if (count & RWSEM_WRITER_MASK)
         return;
 
     if (count & RWSEM_READER_MASK) {
         wake_type = RWSEM_WAKE_READERS;
     } else {
         wake_type = RWSEM_WAKE_ANY;
         clear_nonspinnable(sem);
     }
     rwsem_mark_wake(sem, wake_type, wake_q);
 }
 
 /*
  * 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);
 
     /*
      * 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, 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)) {
             /* 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);
 
     rwsem_cond_wake_waiter(sem, count, &wake_q);
     raw_spin_unlock_irq(&sem->wait_lock);
 
     if (!wake_q_empty(&wake_q))
         wake_up_q(&wake_q);
 
     trace_contention_begin(sem, LCB_F_READ);
 
     /* 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);
     trace_contention_end(sem, 0);
     return sem;
 
 out_nolock:
     rwsem_del_wake_waiter(sem, &waiter, &wake_q);
     __set_current_state(TASK_RUNNING);
     lockevent_inc(rwsem_rlock_fail);
     trace_contention_end(sem, -EINTR);
     return ERR_PTR(-EINTR);
 }
 
 /*
  * Wait until we successfully acquire the write lock
  */
 static struct rw_semaphore __sched *
 rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
 {
     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) {
         rwsem_cond_wake_waiter(sem, atomic_long_read(&sem->count),
                        &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);
             raw_spin_lock_irq(&sem->wait_lock);
         }
     } else {
         atomic_long_or(RWSEM_FLAG_WAITERS, &sem->count);
     }
 
     /* wait until we successfully acquire the lock */
     set_current_state(state);
     trace_contention_begin(sem, LCB_F_WRITE);
 
     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);
     trace_contention_end(sem, 0);
     return sem;
 
 out_nolock:
     __set_current_state(TASK_RUNNING);
     raw_spin_lock_irq(&sem->wait_lock);
     rwsem_del_wake_waiter(sem, &waiter, &wake_q);
     lockevent_inc(rwsem_wlock_fail);
     trace_contention_end(sem, -EINTR);
     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);
 
     tmp = atomic_long_read(&sem->count);
     while (!(tmp & RWSEM_READ_FAILED_MASK)) {
         if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
                             tmp + RWSEM_READER_BIAS)) {
             rwsem_set_reader_owned(sem);
             return 1;
         }
     }
     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

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