include/sys/mutex.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_MUTEX_H
  26 #define _SPL_MUTEX_H
  27
  28 #include <sys/types.h>
  29 #include <linux/mutex.h>
  30 #include <linux/compiler_compat.h>
  31
  32 typedef enum {
  33         MUTEX_DEFAULT   = 0,
  34         MUTEX_SPIN      = 1,
  35         MUTEX_ADAPTIVE  = 2
  36 } kmutex_type_t;
  37
  38 typedef struct {
  39         struct mutex            m_mutex;
  40         spinlock_t              m_lock; /* used for serializing mutex_exit */
  41         kthread_t               *m_owner;
  42 } kmutex_t;
  43
  44 #define MUTEX(mp)               (&((mp)->m_mutex))
  45
  46 static inline void
  47 spl_mutex_set_owner(kmutex_t *mp)
  48 {
  49         mp->m_owner = current;
  50 }
  51
  52 static inline void
  53 spl_mutex_clear_owner(kmutex_t *mp)
  54 {
  55         mp->m_owner = NULL;
  56 }
  57
  58 #define mutex_owner(mp)         (ACCESS_ONCE((mp)->m_owner))
  59 #define mutex_owned(mp)         (mutex_owner(mp) == current)
  60 #define MUTEX_HELD(mp)          mutex_owned(mp)
  61 #define MUTEX_NOT_HELD(mp)      (!MUTEX_HELD(mp))
  62
  63 /*
  64  * The following functions must be a #define and not static inline.
  65  * This ensures that the native linux mutex functions (lock/unlock)
  66  * will be correctly located in the users code which is important
  67  * for the built in kernel lock analysis tools
  68  */
  69 #undef mutex_init
  70 #define mutex_init(mp, name, type, ibc)                         \
  71 {                                                               \
  72         static struct lock_class_key __key;                     \
  73         ASSERT(type == MUTEX_DEFAULT);                          \
  74                                                                 \
  75         __mutex_init(MUTEX(mp), #mp, &__key);                   \
  76         spin_lock_init(&(mp)->m_lock);                          \
  77         spl_mutex_clear_owner(mp);                              \
  78 }
  79
  80 #undef mutex_destroy
  81 #define mutex_destroy(mp)                                       \
  82 {                                                               \
  83         VERIFY3P(mutex_owner(mp), ==, NULL);                    \
  84 }
  85
  86 #define mutex_tryenter(mp)                                      \
  87 ({                                                              \
  88         int _rc_;                                               \
  89                                                                 \
  90         if ((_rc_ = mutex_trylock(MUTEX(mp))) == 1)             \
  91                 spl_mutex_set_owner(mp);                        \
  92                                                                 \
  93         _rc_;                                                   \
  94 })
  95
  96 #define mutex_enter(mp)                                         \
  97 {                                                               \
  98         ASSERT3P(mutex_owner(mp), !=, current);                 \
  99         mutex_lock(MUTEX(mp));                                  \
 100         spl_mutex_set_owner(mp);                                \
 101 }
 102
 103 /*
 104  * The reason for the spinlock:
 105  *
 106  * The Linux mutex is designed with a fast-path/slow-path design such that it
 107  * does not guarantee serialization upon itself, allowing a race where latter
 108  * acquirers finish mutex_unlock before former ones.
 109  *
 110  * The race renders it unsafe to be used for serializing the freeing of an
 111  * object in which the mutex is embedded, where the latter acquirer could go
 112  * on to free the object while the former one is still doing mutex_unlock and
 113  * causing memory corruption.
 114  *
 115  * However, there are many places in ZFS where the mutex is used for
 116  * serializing object freeing, and the code is shared among other OSes without
 117  * this issue. Thus, we need the spinlock to force the serialization on
 118  * mutex_exit().
 119  *
 120  * See http://lwn.net/Articles/575477/ for the information about the race.
 121  */
 122 #define mutex_exit(mp)                                          \
 123 {                                                               \
 124         spin_lock(&(mp)->m_lock);                               \
 125         spl_mutex_clear_owner(mp);                              \
 126         mutex_unlock(MUTEX(mp));                                \
 127         spin_unlock(&(mp)->m_lock);                             \
 128 }
 129
 130 int spl_mutex_init(void);
 131 void spl_mutex_fini(void);
 132
 133 #endif /* _SPL_MUTEX_H */