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 #ifndef HAVE_MUTEX_OWNER
  42         /* only when kernel doesn't have owner */
  43         kthread_t               *m_owner;
  44 #endif
  45 } kmutex_t;
  46
  47 #define MUTEX(mp)               (&((mp)->m_mutex))
  48
  49 static inline void
  50 spl_mutex_set_owner(kmutex_t *mp)
  51 {
  52         /*
  53          * kernel will handle its owner, so we don't need to do anything if it
  54          * is defined.
  55          */
  56 #ifndef HAVE_MUTEX_OWNER
  57         mp->m_owner = current;
  58 #endif
  59 }
  60
  61 static inline void
  62 spl_mutex_clear_owner(kmutex_t *mp)
  63 {
  64 #ifndef HAVE_MUTEX_OWNER
  65         mp->m_owner = NULL;
  66 #endif
  67 }
  68
  69 #ifdef HAVE_MUTEX_OWNER
  70 #define mutex_owner(mp)         (ACCESS_ONCE(MUTEX(mp)->owner))
  71 #else
  72 #define mutex_owner(mp)         (ACCESS_ONCE((mp)->m_owner))
  73 #endif
  74 #define mutex_owned(mp)         (mutex_owner(mp) == current)
  75 #define MUTEX_HELD(mp)          mutex_owned(mp)
  76 #define MUTEX_NOT_HELD(mp)      (!MUTEX_HELD(mp))
  77
  78 /*
  79  * The following functions must be a #define and not static inline.
  80  * This ensures that the native linux mutex functions (lock/unlock)
  81  * will be correctly located in the users code which is important
  82  * for the built in kernel lock analysis tools
  83  */
  84 #undef mutex_init
  85 #define mutex_init(mp, name, type, ibc)                         \
  86 {                                                               \
  87         static struct lock_class_key __key;                     \
  88         ASSERT(type == MUTEX_DEFAULT);                          \
  89                                                                 \
  90         __mutex_init(MUTEX(mp), (name) ? (#name) : (#mp), &__key); \
  91         spin_lock_init(&(mp)->m_lock);                          \
  92         spl_mutex_clear_owner(mp);                              \
  93 }
  94
  95 #undef mutex_destroy
  96 #define mutex_destroy(mp)                                       \
  97 {                                                               \
  98         VERIFY3P(mutex_owner(mp), ==, NULL);                    \
  99 }
 100
 101 #define mutex_tryenter(mp)                                      \
 102 ({                                                              \
 103         int _rc_;                                               \
 104                                                                 \
 105         if ((_rc_ = mutex_trylock(MUTEX(mp))) == 1)             \
 106                 spl_mutex_set_owner(mp);                        \
 107                                                                 \
 108         _rc_;                                                   \
 109 })
 110
 111 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 112 #define mutex_enter_nested(mp, subclass)                        \
 113 {                                                               \
 114         ASSERT3P(mutex_owner(mp), !=, current);                 \
 115         mutex_lock_nested(MUTEX(mp), (subclass));               \
 116         spl_mutex_set_owner(mp);                                \
 117 }
 118 #else /* CONFIG_DEBUG_LOCK_ALLOC */
 119 #define mutex_enter_nested(mp, subclass)                        \
 120 {                                                               \
 121         ASSERT3P(mutex_owner(mp), !=, current);                 \
 122         mutex_lock(MUTEX(mp));                                  \
 123         spl_mutex_set_owner(mp);                                \
 124 }
 125 #endif /*  CONFIG_DEBUG_LOCK_ALLOC */
 126
 127 #define mutex_enter(mp) mutex_enter_nested((mp), 0)
 128
 129 /*
 130  * The reason for the spinlock:
 131  *
 132  * The Linux mutex is designed with a fast-path/slow-path design such that it
 133  * does not guarantee serialization upon itself, allowing a race where latter
 134  * acquirers finish mutex_unlock before former ones.
 135  *
 136  * The race renders it unsafe to be used for serializing the freeing of an
 137  * object in which the mutex is embedded, where the latter acquirer could go
 138  * on to free the object while the former one is still doing mutex_unlock and
 139  * causing memory corruption.
 140  *
 141  * However, there are many places in ZFS where the mutex is used for
 142  * serializing object freeing, and the code is shared among other OSes without
 143  * this issue. Thus, we need the spinlock to force the serialization on
 144  * mutex_exit().
 145  *
 146  * See http://lwn.net/Articles/575477/ for the information about the race.
 147  */
 148 #define mutex_exit(mp)                                          \
 149 {                                                               \
 150         spin_lock(&(mp)->m_lock);                               \
 151         spl_mutex_clear_owner(mp);                              \
 152         mutex_unlock(MUTEX(mp));                                \
 153         spin_unlock(&(mp)->m_lock);                             \
 154 }
 155
 156 int spl_mutex_init(void);
 157 void spl_mutex_fini(void);
 158
 159 #endif /* _SPL_MUTEX_H */