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         RW_NOLOCKDEP    = 5
  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 /*
  45  * If CONFIG_RWSEM_SPIN_ON_OWNER is defined, rw_semaphore will have an owner
  46  * field, so we don't need our own.
  47  */
  48 typedef struct {
  49         struct rw_semaphore rw_rwlock;
  50 #ifndef CONFIG_RWSEM_SPIN_ON_OWNER
  51         kthread_t *rw_owner;
  52 #endif
  53 #ifdef CONFIG_LOCKDEP
  54         krw_type_t      rw_type;
  55 #endif /* CONFIG_LOCKDEP */
  56 } krwlock_t;
  57
  58 #define SEM(rwp)        (&(rwp)->rw_rwlock)
  59
  60 static inline void
  61 spl_rw_set_owner(krwlock_t *rwp)
  62 {
  63 /*
  64  * If CONFIG_RWSEM_SPIN_ON_OWNER is defined, down_write, up_write,
  65  * downgrade_write and __init_rwsem will set/clear owner for us.
  66  */
  67 #ifndef CONFIG_RWSEM_SPIN_ON_OWNER
  68         rwp->rw_owner = current;
  69 #endif
  70 }
  71
  72 static inline void
  73 spl_rw_clear_owner(krwlock_t *rwp)
  74 {
  75 #ifndef CONFIG_RWSEM_SPIN_ON_OWNER
  76         rwp->rw_owner = NULL;
  77 #endif
  78 }
  79
  80 static inline kthread_t *
  81 rw_owner(krwlock_t *rwp)
  82 {
  83 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  84         return SEM(rwp)->owner;
  85 #else
  86         return rwp->rw_owner;
  87 #endif
  88 }
  89
  90 #ifdef CONFIG_LOCKDEP
  91 static inline void
  92 spl_rw_set_type(krwlock_t *rwp, krw_type_t type)
  93 {
  94         rwp->rw_type = type;
  95 }
  96 static inline void
  97 spl_rw_lockdep_off_maybe(krwlock_t *rwp)                \
  98 {                                                       \
  99         if (rwp && rwp->rw_type == RW_NOLOCKDEP)        \
 100                 lockdep_off();                          \
 101 }
 102 static inline void
 103 spl_rw_lockdep_on_maybe(krwlock_t *rwp)                 \
 104 {                                                       \
 105         if (rwp && rwp->rw_type == RW_NOLOCKDEP)        \
 106                 lockdep_on();                           \
 107 }
 108 #else  /* CONFIG_LOCKDEP */
 109 #define spl_rw_set_type(rwp, type)
 110 #define spl_rw_lockdep_off_maybe(rwp)
 111 #define spl_rw_lockdep_on_maybe(rwp)
 112 #endif /* CONFIG_LOCKDEP */
 113
 114 static inline int
 115 RW_READ_HELD(krwlock_t *rwp)
 116 {
 117         return (spl_rwsem_is_locked(SEM(rwp)) && rw_owner(rwp) == NULL);
 118 }
 119
 120 static inline int
 121 RW_WRITE_HELD(krwlock_t *rwp)
 122 {
 123         return (rw_owner(rwp) == current);
 124 }
 125
 126 static inline int
 127 RW_LOCK_HELD(krwlock_t *rwp)
 128 {
 129         return spl_rwsem_is_locked(SEM(rwp));
 130 }
 131
 132 /*
 133  * The following functions must be a #define and not static inline.
 134  * This ensures that the native linux semaphore functions (down/up)
 135  * will be correctly located in the users code which is important
 136  * for the built in kernel lock analysis tools
 137  */
 138 #define rw_init(rwp, name, type, arg)                                   \
 139 ({                                                                      \
 140         static struct lock_class_key __key;                             \
 141         ASSERT(type == RW_DEFAULT || type == RW_NOLOCKDEP);             \
 142                                                                         \
 143         __init_rwsem(SEM(rwp), #rwp, &__key);                           \
 144         spl_rw_clear_owner(rwp);                                        \
 145         spl_rw_set_type(rwp, type);                                     \
 146 })
 147
 148 #define rw_destroy(rwp)                                                 \
 149 ({                                                                      \
 150         VERIFY(!RW_LOCK_HELD(rwp));                                     \
 151 })
 152
 153 #define rw_tryenter(rwp, rw)                                            \
 154 ({                                                                      \
 155         int _rc_ = 0;                                                   \
 156                                                                         \
 157         spl_rw_lockdep_off_maybe(rwp);                                  \
 158         switch (rw) {                                                   \
 159         case RW_READER:                                                 \
 160                 _rc_ = down_read_trylock(SEM(rwp));                     \
 161                 break;                                                  \
 162         case RW_WRITER:                                                 \
 163                 if ((_rc_ = down_write_trylock(SEM(rwp))))              \
 164                         spl_rw_set_owner(rwp);                          \
 165                 break;                                                  \
 166         default:                                                        \
 167                 VERIFY(0);                                              \
 168         }                                                               \
 169         spl_rw_lockdep_on_maybe(rwp);                                   \
 170         _rc_;                                                           \
 171 })
 172
 173 #define rw_enter(rwp, rw)                                               \
 174 ({                                                                      \
 175         spl_rw_lockdep_off_maybe(rwp);                                  \
 176         switch (rw) {                                                   \
 177         case RW_READER:                                                 \
 178                 down_read(SEM(rwp));                                    \
 179                 break;                                                  \
 180         case RW_WRITER:                                                 \
 181                 down_write(SEM(rwp));                                   \
 182                 spl_rw_set_owner(rwp);                                  \
 183                 break;                                                  \
 184         default:                                                        \
 185                 VERIFY(0);                                              \
 186         }                                                               \
 187         spl_rw_lockdep_on_maybe(rwp);                                   \
 188 })
 189
 190 #define rw_exit(rwp)                                                    \
 191 ({                                                                      \
 192         spl_rw_lockdep_off_maybe(rwp);                                  \
 193         if (RW_WRITE_HELD(rwp)) {                                       \
 194                 spl_rw_clear_owner(rwp);                                \
 195                 up_write(SEM(rwp));                                     \
 196         } else {                                                        \
 197                 ASSERT(RW_READ_HELD(rwp));                              \
 198                 up_read(SEM(rwp));                                      \
 199         }                                                               \
 200         spl_rw_lockdep_on_maybe(rwp);                                   \
 201 })
 202
 203 #define rw_downgrade(rwp)                                               \
 204 ({                                                                      \
 205         spl_rw_lockdep_off_maybe(rwp);                                  \
 206         spl_rw_clear_owner(rwp);                                        \
 207         downgrade_write(SEM(rwp));                                      \
 208         spl_rw_lockdep_on_maybe(rwp);                                   \
 209 })
 210
 211 /*
 212  * This implementation of rw_tryupgrade() behaves slightly differently
 213  * from its counterparts on other platforms.  It drops the RW_READER lock
 214  * and then acquires the RW_WRITER lock leaving a small window where no
 215  * lock is held.  On other platforms the lock is never released during
 216  * the upgrade process.  This is necessary under Linux because the kernel
 217  * does not provide an upgrade function.
 218  */
 219 #define rw_tryupgrade(rwp)                                              \
 220 ({                                                                      \
 221         int _rc_ = 0;                                                   \
 222                                                                         \
 223         if (RW_WRITE_HELD(rwp)) {                                       \
 224                 _rc_ = 1;                                               \
 225         } else {                                                        \
 226                 spl_rw_lockdep_off_maybe(rwp);                          \
 227                 if ((_rc_ = rwsem_tryupgrade(SEM(rwp))))                \
 228                         spl_rw_set_owner(rwp);                          \
 229                 spl_rw_lockdep_on_maybe(rwp);                           \
 230         }                                                               \
 231         _rc_;                                                           \
 232 })
 233
 234 int spl_rw_init(void);
 235 void spl_rw_fini(void);
 236
 237 #endif /* _SPL_RWLOCK_H */