include/sys/rwlock.h

   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
  25 #ifndef _SPL_RWLOCK_H
  26 #define _SPL_RWLOCK_H
  27
  28 #include <sys/types.h>
  29 #include <linux/rwsem.h>
  30
  31 typedef enum {
  32         RW_DRIVER  = 2,
  33         RW_DEFAULT = 4
  34 } krw_type_t;
  35
  36 typedef enum {
  37         RW_NONE   = 0,
  38         RW_WRITER = 1,
  39         RW_READER = 2
  40 } krw_t;
  41
  42 typedef struct {
  43         struct rw_semaphore rw_rwlock;
  44         kthread_t *rw_owner;
  45 } krwlock_t;
  46
  47 #define SEM(rwp)                        ((struct rw_semaphore *)(rwp))
  48
  49 static inline kthread_t *
  50 spl_rw_get_owner(krwlock_t *rwp)
  51 {
  52         return rwp->rw_owner;
  53 }
  54
  55 static inline void
  56 spl_rw_set_owner(krwlock_t *rwp)
  57 {
  58         unsigned long flags;
  59
  60         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
  61         rwp->rw_owner = current;
  62         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
  63 }
  64
  65 static inline void
  66 spl_rw_clear_owner(krwlock_t *rwp)
  67 {
  68         unsigned long flags;
  69
  70         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
  71         rwp->rw_owner = NULL;
  72         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
  73 }
  74
  75 static inline kthread_t *
  76 rw_owner(krwlock_t *rwp)
  77 {
  78         unsigned long flags;
  79         kthread_t *owner;
  80
  81         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
  82         owner = spl_rw_get_owner(rwp);
  83         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
  84
  85         return owner;
  86 }
  87
  88 static inline int
  89 RW_READ_HELD(krwlock_t *rwp)
  90 {
  91         unsigned long flags;
  92         int rc;
  93
  94         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
  95         rc = (rwsem_is_locked(SEM(rwp)) && spl_rw_get_owner(rwp) == NULL);
  96         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
  97
  98         return rc;
  99 }
 100
 101 static inline int
 102 RW_WRITE_HELD(krwlock_t *rwp)
 103 {
 104         unsigned long flags;
 105         int rc;
 106
 107         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 108         rc = (rwsem_is_locked(SEM(rwp)) && spl_rw_get_owner(rwp) == current);
 109         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 110
 111         return rc;
 112 }
 113
 114 static inline int
 115 RW_LOCK_HELD(krwlock_t *rwp)
 116 {
 117         unsigned long flags;
 118         int rc;
 119
 120         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 121         rc = rwsem_is_locked(SEM(rwp));
 122         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 123
 124         return rc;
 125 }
 126
 127 /*
 128  * The following functions must be a #define and not static inline.
 129  * This ensures that the native linux semaphore functions (down/up)
 130  * will be correctly located in the users code which is important
 131  * for the built in kernel lock analysis tools
 132  */
 133 #define rw_init(rwp, name, type, arg)                                   \
 134 ({                                                                      \
 135         static struct lock_class_key __key;                             \
 136                                                                         \
 137         __init_rwsem(SEM(rwp), #rwp, &__key);                           \
 138         spl_rw_clear_owner(rwp);                                        \
 139 })
 140
 141 #define rw_destroy(rwp)                                                 \
 142 ({                                                                      \
 143         VERIFY(!RW_LOCK_HELD(rwp));                                     \
 144 })
 145
 146 #define rw_tryenter(rwp, rw)                                            \
 147 ({                                                                      \
 148         int _rc_ = 0;                                                   \
 149                                                                         \
 150         switch (rw) {                                                   \
 151         case RW_READER:                                                 \
 152                 _rc_ = down_read_trylock(SEM(rwp));                     \
 153                 break;                                                  \
 154         case RW_WRITER:                                                 \
 155                 if ((_rc_ = down_write_trylock(SEM(rwp))))              \
 156                         spl_rw_set_owner(rwp);                          \
 157                 break;                                                  \
 158         default:                                                        \
 159                 VERIFY(0);                                              \
 160         }                                                               \
 161         _rc_;                                                           \
 162 })
 163
 164 #define rw_enter(rwp, rw)                                               \
 165 ({                                                                      \
 166         switch (rw) {                                                   \
 167         case RW_READER:                                                 \
 168                 down_read(SEM(rwp));                                    \
 169                 break;                                                  \
 170         case RW_WRITER:                                                 \
 171                 down_write(SEM(rwp));                                   \
 172                 spl_rw_set_owner(rwp);                                  \
 173                 break;                                                  \
 174         default:                                                        \
 175                 VERIFY(0);                                              \
 176         }                                                               \
 177 })
 178
 179 #define rw_exit(rwp)                                                    \
 180 ({                                                                      \
 181         if (RW_WRITE_HELD(rwp)) {                                       \
 182                 spl_rw_clear_owner(rwp);                                \
 183                 up_write(SEM(rwp));                                     \
 184         } else {                                                        \
 185                 ASSERT(RW_READ_HELD(rwp));                              \
 186                 up_read(SEM(rwp));                                      \
 187         }                                                               \
 188 })
 189
 190 #define rw_downgrade(rwp)                                               \
 191 ({                                                                      \
 192         spl_rw_clear_owner(rwp);                                        \
 193         downgrade_write(SEM(rwp));                                      \
 194 })
 195
 196 #if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
 197 /*
 198  * For the generic implementations of rw-semaphores the following is
 199  * true.  If your semaphore implementation internally represents the
 200  * semaphore state differently then special case handling is required.
 201  * - if activity/count is 0 then there are no active readers or writers
 202  * - if activity/count is +ve then that is the number of active readers
 203  * - if activity/count is -1 then there is one active writer
 204  */
 205
 206 extern void __up_read_locked(struct rw_semaphore *);
 207 extern int __down_write_trylock_locked(struct rw_semaphore *);
 208
 209 #define rw_tryupgrade(rwp)                                              \
 210 ({                                                                      \
 211         unsigned long _flags_;                                          \
 212         int _rc_ = 0;                                                   \
 213                                                                         \
 214         spin_lock_irqsave(&SEM(rwp)->wait_lock, _flags_);               \
 215         if ((list_empty(&SEM(rwp)->wait_list)) &&                       \
 216             (SEM(rwp)->activity == 1)) {                                \
 217                 __up_read_locked(SEM(rwp));                             \
 218                 VERIFY(_rc_ = __down_write_trylock_locked(SEM(rwp)));   \
 219                 (rwp)->rw_owner = current;                              \
 220         }                                                               \
 221         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, _flags_);          \
 222         _rc_;                                                           \
 223 })
 224 #else
 225 /*
 226  * rw_tryupgrade() can be implemented correctly but for each supported
 227  * arch we will need a custom implementation.  For the x86 implementation
 228  * it looks like a custom cmpxchg() to atomically check and promote the
 229  * rwsem would be safe.  For now that's not worth the trouble so in this
 230  * case rw_tryupgrade() has just been disabled.
 231  */
 232 #define rw_tryupgrade(rwp)      ({ 0; })
 233 #endif
 234
 235 int spl_rw_init(void);
 236 void spl_rw_fini(void);
 237
 238 #endif /* _SPL_RWLOCK_H */