module/spl/spl-rwlock.c

   1 /*
   2  *  This file is part of the SPL: Solaris Porting Layer.
   3  *
   4  *  Copyright (c) 2008 Lawrence Livermore National Security, LLC.
   5  *  Produced at Lawrence Livermore National Laboratory
   6  *  Written by:
   7  *          Brian Behlendorf <behlendorf1@llnl.gov>,
   8  *          Herb Wartens <wartens2@llnl.gov>,
   9  *          Jim Garlick <garlick@llnl.gov>
  10  *  UCRL-CODE-235197
  11  *
  12  *  This is free software; you can redistribute it and/or modify it
  13  *  under the terms of the GNU General Public License as published by
  14  *  the Free Software Foundation; either version 2 of the License, or
  15  *  (at your option) any later version.
  16  *
  17  *  This is distributed in the hope that it will be useful, but WITHOUT
  18  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  19  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  20  *  for more details.
  21  *
  22  *  You should have received a copy of the GNU General Public License along
  23  *  with this program; if not, write to the Free Software Foundation, Inc.,
  24  *  51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA.
  25  */
  26
  27 #include <sys/rwlock.h>
  28
  29 #ifdef DEBUG_SUBSYSTEM
  30 #undef DEBUG_SUBSYSTEM
  31 #endif
  32
  33 #define DEBUG_SUBSYSTEM S_RWLOCK
  34
  35 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  36
  37 /*
  38  * From lib/rwsem-spinlock.c but modified such that the caller is
  39  * responsible for acquiring and dropping the sem->wait_lock.
  40  */
  41 struct rwsem_waiter {
  42         struct list_head list;
  43         struct task_struct *task;
  44         unsigned int flags;
  45 #define RWSEM_WAITING_FOR_READ  0x00000001
  46 #define RWSEM_WAITING_FOR_WRITE 0x00000002
  47 };
  48
  49 /* wake a single writer */
  50 static struct rw_semaphore *
  51 __rwsem_wake_one_writer_locked(struct rw_semaphore *sem)
  52 {
  53         struct rwsem_waiter *waiter;
  54         struct task_struct *tsk;
  55
  56         sem->activity = -1;
  57
  58         waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
  59         list_del(&waiter->list);
  60
  61         tsk = waiter->task;
  62         smp_mb();
  63         waiter->task = NULL;
  64         wake_up_process(tsk);
  65         put_task_struct(tsk);
  66         return sem;
  67 }
  68
  69 /* release a read lock on the semaphore */
  70 void
  71 __up_read_locked(struct rw_semaphore *sem)
  72 {
  73         if (--sem->activity == 0 && !list_empty(&sem->wait_list))
  74                 (void)__rwsem_wake_one_writer_locked(sem);
  75 }
  76 EXPORT_SYMBOL(__up_read_locked);
  77
  78 /* trylock for writing -- returns 1 if successful, 0 if contention */
  79 int
  80 __down_write_trylock_locked(struct rw_semaphore *sem)
  81 {
  82         int ret = 0;
  83
  84         if (sem->activity == 0 && list_empty(&sem->wait_list)) {
  85                 sem->activity = -1;
  86                 ret = 1;
  87         }
  88
  89         return ret;
  90 }
  91 EXPORT_SYMBOL(__down_write_trylock_locked);
  92
  93 #endif