git.sesse.net Git - bcachefs-tools-debian/blob - libbcachefs/six.h

   1 #ifndef _BCACHEFS_SIX_H
   2 #define _BCACHEFS_SIX_H
   3
   4 /*
   5  * Shared/intent/exclusive locks: sleepable read/write locks, much like rw
   6  * semaphores, except with a third intermediate state, intent. Basic operations
   7  * are:
   8  *
   9  * six_lock_read(&foo->lock);
  10  * six_unlock_read(&foo->lock);
  11  *
  12  * six_lock_intent(&foo->lock);
  13  * six_unlock_intent(&foo->lock);
  14  *
  15  * six_lock_write(&foo->lock);
  16  * six_unlock_write(&foo->lock);
  17  *
  18  * Intent locks block other intent locks, but do not block read locks, and you
  19  * must have an intent lock held before taking a write lock, like so:
  20  *
  21  * six_lock_intent(&foo->lock);
  22  * six_lock_write(&foo->lock);
  23  * six_unlock_write(&foo->lock);
  24  * six_unlock_intent(&foo->lock);
  25  *
  26  * Other operations:
  27  *
  28  *   six_trylock_read()
  29  *   six_trylock_intent()
  30  *   six_trylock_write()
  31  *
  32  *   six_lock_downgrade():      convert from intent to read
  33  *   six_lock_tryupgrade():     attempt to convert from read to intent
  34  *
  35  * Locks also embed a sequence number, which is incremented when the lock is
  36  * locked or unlocked for write. The current sequence number can be grabbed
  37  * while a lock is held from lock->state.seq; then, if you drop the lock you can
  38  * use six_relock_(read|intent_write)(lock, seq) to attempt to retake the lock
  39  * iff it hasn't been locked for write in the meantime.
  40  *
  41  * There are also operations that take the lock type as a parameter, where the
  42  * type is one of SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write:
  43  *
  44  *   six_lock_type(lock, type)
  45  *   six_unlock_type(lock, type)
  46  *   six_relock(lock, type, seq)
  47  *   six_trylock_type(lock, type)
  48  *   six_trylock_convert(lock, from, to)
  49  *
  50  * A lock may be held multiple types by the same thread (for read or intent,
  51  * not write) - up to SIX_LOCK_MAX_RECURSE. However, the six locks code does
  52  * _not_ implement the actual recursive checks itself though - rather, if your
  53  * code (e.g. btree iterator code) knows that the current thread already has a
  54  * lock held, and for the correct type, six_lock_increment() may be used to
  55  * bump up the counter for that type - the only effect is that one more call to
  56  * unlock will be required before the lock is unlocked.
  57  */
  58
  59 #include <linux/lockdep.h>
  60 #include <linux/osq_lock.h>
  61 #include <linux/sched.h>
  62 #include <linux/types.h>
  63
  64 #include "util.h"
  65
  66 #define SIX_LOCK_SEPARATE_LOCKFNS
  67
  68 union six_lock_state {
  69         struct {
  70                 atomic64_t      counter;
  71         };
  72
  73         struct {
  74                 u64             v;
  75         };
  76
  77         struct {
  78                 /* for waitlist_bitnr() */
  79                 unsigned long   l;
  80         };
  81
  82         struct {
  83                 unsigned        read_lock:26;
  84                 unsigned        intent_lock:3;
  85                 unsigned        waiters:3;
  86                 /*
  87                  * seq works much like in seqlocks: it's incremented every time
  88                  * we lock and unlock for write.
  89                  *
  90                  * If it's odd write lock is held, even unlocked.
  91                  *
  92                  * Thus readers can unlock, and then lock again later iff it
  93                  * hasn't been modified in the meantime.
  94                  */
  95                 u32             seq;
  96         };
  97 };
  98
  99 #define SIX_LOCK_MAX_RECURSE    ((1 << 3) - 1)
 100
 101 enum six_lock_type {
 102         SIX_LOCK_read,
 103         SIX_LOCK_intent,
 104         SIX_LOCK_write,
 105 };
 106
 107 struct six_lock {
 108         union six_lock_state    state;
 109         struct task_struct      *owner;
 110         struct optimistic_spin_queue osq;
 111
 112         raw_spinlock_t          wait_lock;
 113         struct list_head        wait_list[2];
 114 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 115         struct lockdep_map      dep_map;
 116 #endif
 117 };
 118
 119 static __always_inline void __six_lock_init(struct six_lock *lock,
 120                                             const char *name,
 121                                             struct lock_class_key *key)
 122 {
 123         atomic64_set(&lock->state.counter, 0);
 124         raw_spin_lock_init(&lock->wait_lock);
 125         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_read]);
 126         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_intent]);
 127 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 128         debug_check_no_locks_freed((void *) lock, sizeof(*lock));
 129         lockdep_init_map(&lock->dep_map, name, key, 0);
 130 #endif
 131 }
 132
 133 #define six_lock_init(lock)                                             \
 134 do {                                                                    \
 135         static struct lock_class_key __key;                             \
 136                                                                         \
 137         __six_lock_init((lock), #lock, &__key);                         \
 138 } while (0)
 139
 140 #define __SIX_VAL(field, _v)    (((union six_lock_state) { .field = _v }).v)
 141
 142 #ifdef SIX_LOCK_SEPARATE_LOCKFNS
 143
 144 #define __SIX_LOCK(type)                                                \
 145 bool six_trylock_##type(struct six_lock *);                             \
 146 bool six_relock_##type(struct six_lock *, u32);                         \
 147 void six_lock_##type(struct six_lock *);                                \
 148 void six_unlock_##type(struct six_lock *);
 149
 150 __SIX_LOCK(read)
 151 __SIX_LOCK(intent)
 152 __SIX_LOCK(write)
 153 #undef __SIX_LOCK
 154
 155 #define SIX_LOCK_DISPATCH(type, fn, ...)                        \
 156         switch (type) {                                         \
 157         case SIX_LOCK_read:                                     \
 158                 return fn##_read(__VA_ARGS__);                  \
 159         case SIX_LOCK_intent:                                   \
 160                 return fn##_intent(__VA_ARGS__);                \
 161         case SIX_LOCK_write:                                    \
 162                 return fn##_write(__VA_ARGS__);                 \
 163         default:                                                \
 164                 BUG();                                          \
 165         }
 166
 167 static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type)
 168 {
 169         SIX_LOCK_DISPATCH(type, six_trylock, lock);
 170 }
 171
 172 static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type,
 173                      unsigned seq)
 174 {
 175         SIX_LOCK_DISPATCH(type, six_relock, lock, seq);
 176 }
 177
 178 static inline void six_lock_type(struct six_lock *lock, enum six_lock_type type)
 179 {
 180         SIX_LOCK_DISPATCH(type, six_lock, lock);
 181 }
 182
 183 static inline void six_unlock_type(struct six_lock *lock, enum six_lock_type type)
 184 {
 185         SIX_LOCK_DISPATCH(type, six_unlock, lock);
 186 }
 187
 188 #else
 189
 190 bool six_trylock_type(struct six_lock *, enum six_lock_type);
 191 bool six_relock_type(struct six_lock *, enum six_lock_type, unsigned);
 192 void six_lock_type(struct six_lock *, enum six_lock_type);
 193 void six_unlock_type(struct six_lock *, enum six_lock_type);
 194
 195 #define __SIX_LOCK(type)                                                \
 196 static __always_inline bool six_trylock_##type(struct six_lock *lock)   \
 197 {                                                                       \
 198         return six_trylock_type(lock, SIX_LOCK_##type);                 \
 199 }                                                                       \
 200                                                                         \
 201 static __always_inline bool six_relock_##type(struct six_lock *lock, u32 seq)\
 202 {                                                                       \
 203         return six_relock_type(lock, SIX_LOCK_##type, seq);             \
 204 }                                                                       \
 205                                                                         \
 206 static __always_inline void six_lock_##type(struct six_lock *lock)      \
 207 {                                                                       \
 208         six_lock_type(lock, SIX_LOCK_##type);                           \
 209 }                                                                       \
 210                                                                         \
 211 static __always_inline void six_unlock_##type(struct six_lock *lock)    \
 212 {                                                                       \
 213         six_unlock_type(lock, SIX_LOCK_##type);                         \
 214 }
 215
 216 __SIX_LOCK(read)
 217 __SIX_LOCK(intent)
 218 __SIX_LOCK(write)
 219 #undef __SIX_LOCK
 220
 221 #endif
 222
 223 void six_lock_downgrade(struct six_lock *);
 224 bool six_lock_tryupgrade(struct six_lock *);
 225 bool six_trylock_convert(struct six_lock *, enum six_lock_type,
 226                          enum six_lock_type);
 227
 228 void six_lock_increment(struct six_lock *, enum six_lock_type);
 229
 230 #endif /* _BCACHEFS_SIX_H */