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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Ldisc rw semaphore
  *
  * The ldisc semaphore is semantically a rw_semaphore but which enforces
  * an alternate policy, namely:
  *   1) Supports lock wait timeouts
  *   2) Write waiter has priority
  *   3) Downgrading is not supported
  *
  * Implementation notes:
  *   1) Upper half of semaphore count is a wait count (differs from rwsem
  *  in that rwsem normalizes the upper half to the wait bias)
  *   2) Lacks overflow checking
  *
  * The generic counting was copied and modified from include/asm-generic/rwsem.h
  * by Paul Mackerras <paulus@samba.org>.
  *
  * The scheduling policy was copied and modified from lib/rwsem.c
  * Written by David Howells (dhowells@redhat.com).
  *
  * This implementation incorporates the write lock stealing work of
  * Michel Lespinasse <walken@google.com>.
  *
  * Copyright (C) 2013 Peter Hurley <peter@hurleysoftware.com>
  */
 
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/atomic.h>
 #include <linux/tty.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/task.h>
 
 
 #if BITS_PER_LONG == 64
 # define LDSEM_ACTIVE_MASK  0xffffffffL
 #else
 # define LDSEM_ACTIVE_MASK  0x0000ffffL
 #endif
 
 #define LDSEM_UNLOCKED      0L
 #define LDSEM_ACTIVE_BIAS   1L
 #define LDSEM_WAIT_BIAS     (-LDSEM_ACTIVE_MASK-1)
 #define LDSEM_READ_BIAS     LDSEM_ACTIVE_BIAS
 #define LDSEM_WRITE_BIAS    (LDSEM_WAIT_BIAS + LDSEM_ACTIVE_BIAS)
 
 struct ldsem_waiter {
     struct list_head list;
     struct task_struct *task;
 };
 
 /*
  * Initialize an ldsem:
  */
 void __init_ldsem(struct ld_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(&sem->dep_map, name, key, 0);
 #endif
     atomic_long_set(&sem->count, LDSEM_UNLOCKED);
     sem->wait_readers = 0;
     raw_spin_lock_init(&sem->wait_lock);
     INIT_LIST_HEAD(&sem->read_wait);
     INIT_LIST_HEAD(&sem->write_wait);
 }
 
 static void __ldsem_wake_readers(struct ld_semaphore *sem)
 {
     struct ldsem_waiter *waiter, *next;
     struct task_struct *tsk;
     long adjust, count;
 
     /*
      * Try to grant read locks to all readers on the read wait list.
      * Note the 'active part' of the count is incremented by
      * the number of readers before waking any processes up.
      */
     adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
     count = atomic_long_add_return(adjust, &sem->count);
     do {
         if (count > 0)
             break;
         if (atomic_long_try_cmpxchg(&sem->count, &count, count - adjust))
             return;
     } while (1);
 
     list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
         tsk = waiter->task;
         smp_store_release(&waiter->task, NULL);
         wake_up_process(tsk);
         put_task_struct(tsk);
     }
     INIT_LIST_HEAD(&sem->read_wait);
     sem->wait_readers = 0;
 }
 
 static inline int writer_trylock(struct ld_semaphore *sem)
 {
     /*
      * Only wake this writer if the active part of the count can be
      * transitioned from 0 -> 1
      */
     long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
     do {
         if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
             return 1;
         if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
             return 0;
     } while (1);
 }
 
 static void __ldsem_wake_writer(struct ld_semaphore *sem)
 {
     struct ldsem_waiter *waiter;
 
     waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
     wake_up_process(waiter->task);
 }
 
 /*
  * handle the lock release when processes blocked on it that can now run
  * - if we come here from up_xxxx(), then:
  *   - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
  *   - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
  * - the spinlock must be held by the caller
  * - woken process blocks are discarded from the list after having task zeroed
  */
 static void __ldsem_wake(struct ld_semaphore *sem)
 {
     if (!list_empty(&sem->write_wait))
         __ldsem_wake_writer(sem);
     else if (!list_empty(&sem->read_wait))
         __ldsem_wake_readers(sem);
 }
 
 static void ldsem_wake(struct ld_semaphore *sem)
 {
     unsigned long flags;
 
     raw_spin_lock_irqsave(&sem->wait_lock, flags);
     __ldsem_wake(sem);
     raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 }
 
 /*
  * wait for the read lock to be granted
  */
 static struct ld_semaphore __sched *
 down_read_failed(struct ld_semaphore *sem, long count, long timeout)
 {
     struct ldsem_waiter waiter;
     long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;
 
     /* set up my own style of waitqueue */
     raw_spin_lock_irq(&sem->wait_lock);
 
     /*
      * Try to reverse the lock attempt but if the count has changed
      * so that reversing fails, check if there are no waiters,
      * and early-out if not
      */
     do {
         if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
             count += adjust;
             break;
         }
         if (count > 0) {
             raw_spin_unlock_irq(&sem->wait_lock);
             return sem;
         }
     } while (1);
 
     list_add_tail(&waiter.list, &sem->read_wait);
     sem->wait_readers++;
 
     waiter.task = current;
     get_task_struct(current);
 
     /* if there are no active locks, wake the new lock owner(s) */
     if ((count & LDSEM_ACTIVE_MASK) == 0)
         __ldsem_wake(sem);
 
     raw_spin_unlock_irq(&sem->wait_lock);
 
     /* wait to be given the lock */
     for (;;) {
         set_current_state(TASK_UNINTERRUPTIBLE);
 
         if (!smp_load_acquire(&waiter.task))
             break;
         if (!timeout)
             break;
         timeout = schedule_timeout(timeout);
     }
 
     __set_current_state(TASK_RUNNING);
 
     if (!timeout) {
         /*
          * Lock timed out but check if this task was just
          * granted lock ownership - if so, pretend there
          * was no timeout; otherwise, cleanup lock wait.
          */
         raw_spin_lock_irq(&sem->wait_lock);
         if (waiter.task) {
             atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
             sem->wait_readers--;
             list_del(&waiter.list);
             raw_spin_unlock_irq(&sem->wait_lock);
             put_task_struct(waiter.task);
             return NULL;
         }
         raw_spin_unlock_irq(&sem->wait_lock);
     }
 
     return sem;
 }
 
 /*
  * wait for the write lock to be granted
  */
 static struct ld_semaphore __sched *
 down_write_failed(struct ld_semaphore *sem, long count, long timeout)
 {
     struct ldsem_waiter waiter;
     long adjust = -LDSEM_ACTIVE_BIAS;
     int locked = 0;
 
     /* set up my own style of waitqueue */
     raw_spin_lock_irq(&sem->wait_lock);
 
     /*
      * Try to reverse the lock attempt but if the count has changed
      * so that reversing fails, check if the lock is now owned,
      * and early-out if so.
      */
     do {
         if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
             break;
         if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
             raw_spin_unlock_irq(&sem->wait_lock);
             return sem;
         }
     } while (1);
 
     list_add_tail(&waiter.list, &sem->write_wait);
 
     waiter.task = current;
 
     set_current_state(TASK_UNINTERRUPTIBLE);
     for (;;) {
         if (!timeout)
             break;
         raw_spin_unlock_irq(&sem->wait_lock);
         timeout = schedule_timeout(timeout);
         raw_spin_lock_irq(&sem->wait_lock);
         set_current_state(TASK_UNINTERRUPTIBLE);
         locked = writer_trylock(sem);
         if (locked)
             break;
     }
 
     if (!locked)
         atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
     list_del(&waiter.list);
 
     /*
      * In case of timeout, wake up every reader who gave the right of way
      * to writer. Prevent separation readers into two groups:
      * one that helds semaphore and another that sleeps.
      * (in case of no contention with a writer)
      */
     if (!locked && list_empty(&sem->write_wait))
         __ldsem_wake_readers(sem);
 
     raw_spin_unlock_irq(&sem->wait_lock);
 
     __set_current_state(TASK_RUNNING);
 
     /* lock wait may have timed out */
     if (!locked)
         return NULL;
     return sem;
 }
 
 
 
 static int __ldsem_down_read_nested(struct ld_semaphore *sem,
                        int subclass, long timeout)
 {
     long count;
 
     rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 
     count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
     if (count <= 0) {
         lock_contended(&sem->dep_map, _RET_IP_);
         if (!down_read_failed(sem, count, timeout)) {
             rwsem_release(&sem->dep_map, _RET_IP_);
             return 0;
         }
     }
     lock_acquired(&sem->dep_map, _RET_IP_);
     return 1;
 }
 
 static int __ldsem_down_write_nested(struct ld_semaphore *sem,
                         int subclass, long timeout)
 {
     long count;
 
     rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 
     count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
     if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
         lock_contended(&sem->dep_map, _RET_IP_);
         if (!down_write_failed(sem, count, timeout)) {
             rwsem_release(&sem->dep_map, _RET_IP_);
             return 0;
         }
     }
     lock_acquired(&sem->dep_map, _RET_IP_);
     return 1;
 }
 
 
 /*
  * lock for reading -- returns 1 if successful, 0 if timed out
  */
 int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
 {
     might_sleep();
     return __ldsem_down_read_nested(sem, 0, timeout);
 }
 
 /*
  * trylock for reading -- returns 1 if successful, 0 if contention
  */
 int ldsem_down_read_trylock(struct ld_semaphore *sem)
 {
     long count = atomic_long_read(&sem->count);
 
     while (count >= 0) {
         if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
             rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
             lock_acquired(&sem->dep_map, _RET_IP_);
             return 1;
         }
     }
     return 0;
 }
 
 /*
  * lock for writing -- returns 1 if successful, 0 if timed out
  */
 int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
 {
     might_sleep();
     return __ldsem_down_write_nested(sem, 0, timeout);
 }
 
 /*
  * trylock for writing -- returns 1 if successful, 0 if contention
  */
 int ldsem_down_write_trylock(struct ld_semaphore *sem)
 {
     long count = atomic_long_read(&sem->count);
 
     while ((count & LDSEM_ACTIVE_MASK) == 0) {
         if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_WRITE_BIAS)) {
             rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
             lock_acquired(&sem->dep_map, _RET_IP_);
             return 1;
         }
     }
     return 0;
 }
 
 /*
  * release a read lock
  */
 void ldsem_up_read(struct ld_semaphore *sem)
 {
     long count;
 
     rwsem_release(&sem->dep_map, _RET_IP_);
 
     count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
     if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
         ldsem_wake(sem);
 }
 
 /*
  * release a write lock
  */
 void ldsem_up_write(struct ld_semaphore *sem)
 {
     long count;
 
     rwsem_release(&sem->dep_map, _RET_IP_);
 
     count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
     if (count < 0)
         ldsem_wake(sem);
 }
 
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 
 int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
 {
     might_sleep();
     return __ldsem_down_read_nested(sem, subclass, timeout);
 }
 
 int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
                 long timeout)
 {
     might_sleep();
     return __ldsem_down_write_nested(sem, subclass, timeout);
 }
 
 #endif

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