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         /*
  87          * Linux 4.8 will set owner to 1 when read held instead of leave it
  88          * NULL. So we check whether owner <= 1.
  89          */
  90         return (spl_rwsem_is_locked(SEM(rwp)) &&
  91             (unsigned long)rw_owner(rwp) <= 1);
  92 }
  93
  94 static inline int
  95 RW_WRITE_HELD(krwlock_t *rwp)
  96 {
  97         return (spl_rwsem_is_locked(SEM(rwp)) && rw_owner(rwp) == current);
  98 }
  99
 100 static inline int
 101 RW_LOCK_HELD(krwlock_t *rwp)
 102 {
 103         return spl_rwsem_is_locked(SEM(rwp));
 104 }
 105
 106 /*
 107  * The following functions must be a #define and not static inline.
 108  * This ensures that the native linux semaphore functions (down/up)
 109  * will be correctly located in the users code which is important
 110  * for the built in kernel lock analysis tools
 111  */
 112 #define rw_init(rwp, name, type, arg)                                   \
 113 ({                                                                      \
 114         static struct lock_class_key __key;                             \
 115                                                                         \
 116         __init_rwsem(SEM(rwp), #rwp, &__key);                           \
 117         spl_rw_clear_owner(rwp);                                        \
 118 })
 119
 120 #define rw_destroy(rwp)                                                 \
 121 ({                                                                      \
 122         VERIFY(!RW_LOCK_HELD(rwp));                                     \
 123 })
 124
 125 #define rw_tryenter(rwp, rw)                                            \
 126 ({                                                                      \
 127         int _rc_ = 0;                                                   \
 128                                                                         \
 129         switch (rw) {                                                   \
 130         case RW_READER:                                                 \
 131                 _rc_ = down_read_trylock(SEM(rwp));                     \
 132                 break;                                                  \
 133         case RW_WRITER:                                                 \
 134                 if ((_rc_ = down_write_trylock(SEM(rwp))))              \
 135                         spl_rw_set_owner(rwp);                          \
 136                 break;                                                  \
 137         default:                                                        \
 138                 VERIFY(0);                                              \
 139         }                                                               \
 140         _rc_;                                                           \
 141 })
 142
 143 #define rw_enter(rwp, rw)                                               \
 144 ({                                                                      \
 145         switch (rw) {                                                   \
 146         case RW_READER:                                                 \
 147                 down_read(SEM(rwp));                                    \
 148                 break;                                                  \
 149         case RW_WRITER:                                                 \
 150                 down_write(SEM(rwp));                                   \
 151                 spl_rw_set_owner(rwp);                                  \
 152                 break;                                                  \
 153         default:                                                        \
 154                 VERIFY(0);                                              \
 155         }                                                               \
 156 })
 157
 158 #define rw_exit(rwp)                                                    \
 159 ({                                                                      \
 160         if (RW_WRITE_HELD(rwp)) {                                       \
 161                 spl_rw_clear_owner(rwp);                                \
 162                 up_write(SEM(rwp));                                     \
 163         } else {                                                        \
 164                 ASSERT(RW_READ_HELD(rwp));                              \
 165                 up_read(SEM(rwp));                                      \
 166         }                                                               \
 167 })
 168
 169 #define rw_downgrade(rwp)                                               \
 170 ({                                                                      \
 171         spl_rw_clear_owner(rwp);                                        \
 172         downgrade_write(SEM(rwp));                                      \
 173 })
 174
 175 /*
 176  * This implementation of rw_tryupgrade() behaves slightly differently
 177  * from its counterparts on other platforms.  It drops the RW_READER lock
 178  * and then acquires the RW_WRITER lock leaving a small window where no
 179  * lock is held.  On other platforms the lock is never released during
 180  * the upgrade process.  This is necessary under Linux because the kernel
 181  * does not provide an upgrade function.
 182  */
 183 #define rw_tryupgrade(rwp)                                              \
 184 ({                                                                      \
 185         int _rc_ = 0;                                                   \
 186                                                                         \
 187         if (RW_WRITE_HELD(rwp)) {                                       \
 188                 _rc_ = 1;                                               \
 189         } else {                                                        \
 190                 if ((_rc_ = rwsem_tryupgrade(SEM(rwp))))                \
 191                         spl_rw_set_owner(rwp);                          \
 192         }                                                               \
 193         _rc_;                                                           \
 194 })
 195
 196 int spl_rw_init(void);
 197 void spl_rw_fini(void);
 198
 199 #endif /* _SPL_RWLOCK_H */