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