include/sys/rwlock.h

   1 /*
   2  *  This file is part of the SPL: Solaris Porting Layer.
   3  *
   4  *  Copyright (c) 2009 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 #ifndef _SPL_RWLOCK_H
  28 #define _SPL_RWLOCK_H
  29
  30 #include <sys/types.h>
  31 #include <linux/rwsem.h>
  32
  33 typedef enum {
  34         RW_DRIVER  = 2,
  35         RW_DEFAULT = 4
  36 } krw_type_t;
  37
  38 typedef enum {
  39         RW_NONE   = 0,
  40         RW_WRITER = 1,
  41         RW_READER = 2
  42 } krw_t;
  43
  44 typedef struct {
  45         struct rw_semaphore rw_rwlock;
  46         kthread_t *rw_owner;
  47 } krwlock_t;
  48
  49 /*
  50  * For the generic implementations of rw-semaphores the following is
  51  * true.  If your semaphore implementation internally represents the
  52  * semaphore state differently.  Then special case handling will be
  53  * required so RW_COUNT() provides these semantics:
  54  * - if activity/count is 0 then there are no active readers or writers
  55  * - if activity/count is +ve then that is the number of active readers
  56  * - if activity/count is -1 then there is one active writer
  57  */
  58 #define SEM(rwp)                        ((struct rw_semaphore *)(rwp))
  59
  60 #if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
  61 # define RW_COUNT(rwp)                  (SEM(rwp)->activity)
  62 # define rw_exit_locked(rwp)            __up_read_locked(rwp)
  63 # define rw_tryenter_locked(rwp)        __down_write_trylock_locked(rwp)
  64 extern void __up_read_locked(struct rw_semaphore *);
  65 extern int __down_write_trylock_locked(struct rw_semaphore *);
  66 #else
  67 /*
  68  * 2.6.x  - 2.6.27  use guard macro _I386_RWSEM_H
  69  * 2.6.28 - 2.6.32+ use guard macro _ASM_X86_RWSEM_H
  70  */
  71 # if defined(_I386_RWSEM_H) || defined(_ASM_X86_RWSEM_H)
  72 #  define RW_COUNT(rwp)                 ((SEM(rwp)->count < 0) ? (-1) : \
  73                                         (SEM(rwp)->count & RWSEM_ACTIVE_MASK))
  74 # else
  75 #  define RW_COUNT(rwp)                 (SEM(rwp)->count & RWSEM_ACTIVE_MASK)
  76 # endif
  77 # define rw_exit_locked(rwp)           up_read(rwp)
  78 # define rw_tryenter_locked(rwp)       down_write_trylock(rwp)
  79 #endif
  80
  81 static inline kthread_t *
  82 spl_rw_get_owner(krwlock_t *rwp)
  83 {
  84         return rwp->rw_owner;
  85 }
  86
  87 static inline void
  88 spl_rw_set_owner(krwlock_t *rwp)
  89 {
  90         unsigned long flags;
  91
  92         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
  93         rwp->rw_owner = current;
  94         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
  95 }
  96
  97 static inline void
  98 spl_rw_clear_owner(krwlock_t *rwp)
  99 {
 100         unsigned long flags;
 101
 102         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 103         rwp->rw_owner = NULL;
 104         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 105 }
 106
 107 static inline kthread_t *
 108 rw_owner(krwlock_t *rwp)
 109 {
 110         unsigned long flags;
 111         kthread_t *owner;
 112
 113         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 114         owner = spl_rw_get_owner(rwp);
 115         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 116
 117         return owner;
 118 }
 119
 120 static inline int
 121 RW_READ_HELD(krwlock_t *rwp)
 122 {
 123         unsigned long flags;
 124         int rc;
 125
 126         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 127         rc = ((RW_COUNT(rwp) > 0) && (spl_rw_get_owner(rwp) == NULL));
 128         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 129
 130         return rc;
 131 }
 132
 133 static inline int
 134 RW_WRITE_HELD(krwlock_t *rwp)
 135 {
 136         unsigned long flags;
 137         int rc;
 138
 139         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 140         rc = ((RW_COUNT(rwp) < 0) && (spl_rw_get_owner(rwp) == current));
 141         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 142
 143         return rc;
 144 }
 145
 146 static inline int
 147 RW_LOCK_HELD(krwlock_t *rwp)
 148 {
 149         unsigned long flags;
 150         int rc;
 151
 152         spin_lock_irqsave(&SEM(rwp)->wait_lock, flags);
 153         rc = (RW_COUNT(rwp) != 0);
 154         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, flags);
 155
 156         return rc;
 157 }
 158
 159 /*
 160  * The following functions must be a #define and not static inline.
 161  * This ensures that the native linux semaphore functions (down/up)
 162  * will be correctly located in the users code which is important
 163  * for the built in kernel lock analysis tools
 164  */
 165 #define rw_init(rwp, name, type, arg)                                   \
 166 ({                                                                      \
 167         static struct lock_class_key __key;                             \
 168                                                                         \
 169         __init_rwsem(SEM(rwp), #rwp, &__key);                           \
 170         spl_rw_clear_owner(rwp);                                        \
 171 })
 172
 173 #define rw_destroy(rwp)                                                 \
 174 ({                                                                      \
 175         VERIFY(!RW_LOCK_HELD(rwp));                                     \
 176 })
 177
 178 #define rw_tryenter(rwp, rw)                                            \
 179 ({                                                                      \
 180         int _rc_ = 0;                                                   \
 181                                                                         \
 182         switch (rw) {                                                   \
 183         case RW_READER:                                                 \
 184                 _rc_ = down_read_trylock(SEM(rwp));                     \
 185                 break;                                                  \
 186         case RW_WRITER:                                                 \
 187                 if ((_rc_ = down_write_trylock(SEM(rwp))))              \
 188                         spl_rw_set_owner(rwp);                          \
 189                 break;                                                  \
 190         default:                                                        \
 191                 SBUG();                                                 \
 192         }                                                               \
 193         _rc_;                                                           \
 194 })
 195
 196 #define rw_enter(rwp, rw)                                               \
 197 ({                                                                      \
 198         switch (rw) {                                                   \
 199         case RW_READER:                                                 \
 200                 down_read(SEM(rwp));                                    \
 201                 break;                                                  \
 202         case RW_WRITER:                                                 \
 203                 down_write(SEM(rwp));                                   \
 204                 spl_rw_set_owner(rwp);                                  \
 205                 break;                                                  \
 206         default:                                                        \
 207                 SBUG();                                                 \
 208         }                                                               \
 209 })
 210
 211 #define rw_exit(rwp)                                                    \
 212 ({                                                                      \
 213         if (RW_WRITE_HELD(rwp)) {                                       \
 214                 spl_rw_clear_owner(rwp);                                \
 215                 up_write(SEM(rwp));                                     \
 216         } else {                                                        \
 217                 ASSERT(RW_READ_HELD(rwp));                              \
 218                 up_read(SEM(rwp));                                      \
 219         }                                                               \
 220 })
 221
 222 #define rw_downgrade(rwp)                                               \
 223 ({                                                                      \
 224         spl_rw_clear_owner(rwp);                                        \
 225         downgrade_write(SEM(rwp));                                      \
 226 })
 227
 228 #if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
 229 #define rw_tryupgrade(rwp)                                              \
 230 ({                                                                      \
 231         unsigned long _flags_;                                          \
 232         int _rc_ = 0;                                                   \
 233                                                                         \
 234         spin_lock_irqsave(&SEM(rwp)->wait_lock, _flags_);               \
 235         if (list_empty(&SEM(rwp)->wait_list) && (RW_COUNT(rwp) == 1)) { \
 236                 rw_exit_locked(SEM(rwp));                               \
 237                 VERIFY(_rc_ = rw_tryenter_locked(SEM(rwp)));            \
 238                 (rwp)->rw_owner = current;                              \
 239         }                                                               \
 240         spin_unlock_irqrestore(&SEM(rwp)->wait_lock, _flags_);          \
 241         _rc_;                                                           \
 242 })
 243 #else
 244 /*
 245  * This can be done correctly but for each supported arch we will need
 246  * a custom cmpxchg() to atomically check and promote the rwsem.  That's
 247  * not worth the trouble for now so rw_tryupgrade() will always fail.
 248  */
 249 #define rw_tryupgrade(rwp)      ({ 0; })
 250 #endif
 251
 252 int spl_rw_init(void);
 253 void spl_rw_fini(void);
 254
 255 #endif /* _SPL_RWLOCK_H */