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://zfsonlinux.org/>.
  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 #if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
  36 static int
  37 __rwsem_tryupgrade(struct rw_semaphore *rwsem)
  38 {
  39         int ret = 0;
  40         unsigned long flags;
  41         spl_rwsem_lock_irqsave(&rwsem->wait_lock, flags);
  42         if (RWSEM_COUNT(rwsem) == SPL_RWSEM_SINGLE_READER_VALUE &&
  43             list_empty(&rwsem->wait_list)) {
  44                 ret = 1;
  45                 RWSEM_COUNT(rwsem) = SPL_RWSEM_SINGLE_WRITER_VALUE;
  46         }
  47         spl_rwsem_unlock_irqrestore(&rwsem->wait_lock, flags);
  48         return (ret);
  49 }
  50 #elif defined(HAVE_RWSEM_ATOMIC_LONG_COUNT)
  51 static int
  52 __rwsem_tryupgrade(struct rw_semaphore *rwsem)
  53 {
  54         long val;
  55         val = atomic_long_cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
  56             SPL_RWSEM_SINGLE_WRITER_VALUE);
  57         return (val == SPL_RWSEM_SINGLE_READER_VALUE);
  58 }
  59 #else
  60 static int
  61 __rwsem_tryupgrade(struct rw_semaphore *rwsem)
  62 {
  63         typeof (rwsem->count) val;
  64         val = cmpxchg(&rwsem->count, SPL_RWSEM_SINGLE_READER_VALUE,
  65             SPL_RWSEM_SINGLE_WRITER_VALUE);
  66         return (val == SPL_RWSEM_SINGLE_READER_VALUE);
  67 }
  68 #endif
  69
  70 int
  71 rwsem_tryupgrade(struct rw_semaphore *rwsem)
  72 {
  73         if (__rwsem_tryupgrade(rwsem)) {
  74                 rwsem_release(&rwsem->dep_map, 1, _RET_IP_);
  75                 rwsem_acquire(&rwsem->dep_map, 0, 1, _RET_IP_);
  76 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  77                 rwsem->owner = current;
  78 #endif
  79                 return (1);
  80         }
  81         return (0);
  82 }
  83 EXPORT_SYMBOL(rwsem_tryupgrade);
  84
  85 int spl_rw_init(void) { return 0; }
  86 void spl_rw_fini(void) { }