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