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