module/spl/spl-rwlock.c

   1 /*****************************************************************************\
   2  *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
   3  *  Copyright (C) 2007 The Regents of the University of California.
   4  *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
   5  *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
   6  *  UCRL-CODE-235197
   7  *
   8  *  This file is part of the SPL, Solaris Porting Layer.
   9  *  For details, see <http://github.com/behlendorf/spl/>.
  10  *
  11  *  The SPL is free software; you can redistribute it and/or modify it
  12  *  under the terms of the GNU General Public License as published by the
  13  *  Free Software Foundation; either version 2 of the License, or (at your
  14  *  option) any later version.
  15  *
  16  *  The SPL is distributed in the hope that it will be useful, but WITHOUT
  17  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  18  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  19  *  for more details.
  20  *
  21  *  You should have received a copy of the GNU General Public License along
  22  *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
  23  *****************************************************************************
  24  *  Solaris Porting Layer (SPL) Reader/Writer Lock Implementation.
  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
  94
  95 int spl_rw_init(void) { return 0; }
  96 void spl_rw_fini(void) { }