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)) &&
  87                 rw_owner(rwp) == NULL);
  88 }
  89
  90 static inline int
  91 RW_WRITE_HELD(krwlock_t *rwp)
  92 {
  93         return (spl_rwsem_is_locked(SEM(rwp)) &&
  94                 rw_owner(rwp) == current);
  95 }
  96
  97 static inline int
  98 RW_LOCK_HELD(krwlock_t *rwp)
  99 {
 100         return spl_rwsem_is_locked(SEM(rwp));
 101 }
 102
 103 /*
 104  * The following functions must be a #define and not static inline.
 105  * This ensures that the native linux semaphore functions (down/up)
 106  * will be correctly located in the users code which is important
 107  * for the built in kernel lock analysis tools
 108  */
 109 #define rw_init(rwp, name, type, arg)                                   \
 110 ({                                                                      \
 111         static struct lock_class_key __key;                             \
 112                                                                         \
 113         __init_rwsem(SEM(rwp), #rwp, &__key);                           \
 114         spl_rw_clear_owner(rwp);                                        \
 115 })
 116
 117 #define rw_destroy(rwp)                                                 \
 118 ({                                                                      \
 119         VERIFY(!RW_LOCK_HELD(rwp));                                     \
 120 })
 121
 122 #define rw_tryenter(rwp, rw)                                            \
 123 ({                                                                      \
 124         int _rc_ = 0;                                                   \
 125                                                                         \
 126         switch (rw) {                                                   \
 127         case RW_READER:                                                 \
 128                 _rc_ = down_read_trylock(SEM(rwp));                     \
 129                 break;                                                  \
 130         case RW_WRITER:                                                 \
 131                 if ((_rc_ = down_write_trylock(SEM(rwp))))              \
 132                         spl_rw_set_owner(rwp);                          \
 133                 break;                                                  \
 134         default:                                                        \
 135                 VERIFY(0);                                              \
 136         }                                                               \
 137         _rc_;                                                           \
 138 })
 139
 140 #define rw_enter(rwp, rw)                                               \
 141 ({                                                                      \
 142         switch (rw) {                                                   \
 143         case RW_READER:                                                 \
 144                 down_read(SEM(rwp));                                    \
 145                 break;                                                  \
 146         case RW_WRITER:                                                 \
 147                 down_write(SEM(rwp));                                   \
 148                 spl_rw_set_owner(rwp);                                  \
 149                 break;                                                  \
 150         default:                                                        \
 151                 VERIFY(0);                                              \
 152         }                                                               \
 153 })
 154
 155 #define rw_exit(rwp)                                                    \
 156 ({                                                                      \
 157         if (RW_WRITE_HELD(rwp)) {                                       \
 158                 spl_rw_clear_owner(rwp);                                \
 159                 up_write(SEM(rwp));                                     \
 160         } else {                                                        \
 161                 ASSERT(RW_READ_HELD(rwp));                              \
 162                 up_read(SEM(rwp));                                      \
 163         }                                                               \
 164 })
 165
 166 #define rw_downgrade(rwp)                                               \
 167 ({                                                                      \
 168         spl_rw_clear_owner(rwp);                                        \
 169         downgrade_write(SEM(rwp));                                      \
 170 })
 171
 172 #if defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
 173 /*
 174  * For the generic implementations of rw-semaphores the following is
 175  * true.  If your semaphore implementation internally represents the
 176  * semaphore state differently then special case handling is required.
 177  * - if activity/count is 0 then there are no active readers or writers
 178  * - if activity/count is +ve then that is the number of active readers
 179  * - if activity/count is -1 then there is one active writer
 180  */
 181
 182 extern void __up_read_locked(struct rw_semaphore *);
 183 extern int __down_write_trylock_locked(struct rw_semaphore *);
 184
 185 #define rw_tryupgrade(rwp)                                              \
 186 ({                                                                      \
 187         unsigned long _flags_;                                          \
 188         int _rc_ = 0;                                                   \
 189                                                                         \
 190         spl_rwsem_lock_irqsave(&SEM(rwp)->wait_lock, _flags_);           \
 191         if ((list_empty(&SEM(rwp)->wait_list)) &&                       \
 192             (SEM(rwp)->activity == 1)) {                                \
 193                 __up_read_locked(SEM(rwp));                             \
 194                 VERIFY(_rc_ = __down_write_trylock_locked(SEM(rwp)));   \
 195                 (rwp)->rw_owner = current;                              \
 196         }                                                               \
 197         spl_rwsem_unlock_irqrestore(&SEM(rwp)->wait_lock, _flags_);      \
 198         _rc_;                                                           \
 199 })
 200 #else
 201 /*
 202  * rw_tryupgrade() can be implemented correctly but for each supported
 203  * arch we will need a custom implementation.  For the x86 implementation
 204  * it looks like a custom cmpxchg() to atomically check and promote the
 205  * rwsem would be safe.  For now that's not worth the trouble so in this
 206  * case rw_tryupgrade() has just been disabled.
 207  */
 208 #define rw_tryupgrade(rwp)      ({ 0; })
 209 #endif
 210
 211 int spl_rw_init(void);
 212 void spl_rw_fini(void);
 213
 214 #endif /* _SPL_RWLOCK_H */