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

   1 #ifndef _BCACHEFS_SIX_H
   2 #define _BCACHEFS_SIX_H
   3
   4 #include <linux/lockdep.h>
   5 #include <linux/osq_lock.h>
   6 #include <linux/sched.h>
   7 #include <linux/types.h>
   8
   9 #include "util.h"
  10
  11 /*
  12  * LOCK STATES:
  13  *
  14  * read, intent, write (i.e. shared/intent/exclusive, hence the name)
  15  *
  16  * read and write work as with normal read/write locks - a lock can have
  17  * multiple readers, but write excludes reads and other write locks.
  18  *
  19  * Intent does not block read, but it does block other intent locks. The idea is
  20  * by taking an intent lock, you can then later upgrade to a write lock without
  21  * dropping your read lock and without deadlocking - because no other thread has
  22  * the intent lock and thus no other thread could be trying to take the write
  23  * lock.
  24  */
  25
  26 union six_lock_state {
  27         struct {
  28                 atomic64_t      counter;
  29         };
  30
  31         struct {
  32                 u64             v;
  33         };
  34
  35         struct {
  36                 /* for waitlist_bitnr() */
  37                 unsigned long   l;
  38         };
  39
  40         struct {
  41                 unsigned        read_lock:26;
  42                 unsigned        intent_lock:3;
  43                 unsigned        waiters:3;
  44                 /*
  45                  * seq works much like in seqlocks: it's incremented every time
  46                  * we lock and unlock for write.
  47                  *
  48                  * If it's odd write lock is held, even unlocked.
  49                  *
  50                  * Thus readers can unlock, and then lock again later iff it
  51                  * hasn't been modified in the meantime.
  52                  */
  53                 u32             seq;
  54         };
  55 };
  56
  57 #define SIX_LOCK_MAX_RECURSE    ((1 << 3) - 1)
  58
  59 enum six_lock_type {
  60         SIX_LOCK_read,
  61         SIX_LOCK_intent,
  62         SIX_LOCK_write,
  63 };
  64
  65 struct six_lock {
  66         union six_lock_state    state;
  67         struct task_struct      *owner;
  68         struct optimistic_spin_queue osq;
  69
  70         raw_spinlock_t          wait_lock;
  71         struct list_head        wait_list[3];
  72 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  73         struct lockdep_map      dep_map;
  74 #endif
  75 };
  76
  77 static __always_inline void __six_lock_init(struct six_lock *lock,
  78                                             const char *name,
  79                                             struct lock_class_key *key)
  80 {
  81         atomic64_set(&lock->state.counter, 0);
  82         raw_spin_lock_init(&lock->wait_lock);
  83         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_read]);
  84         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_intent]);
  85         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_write]);
  86 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  87         debug_check_no_locks_freed((void *) lock, sizeof(*lock));
  88         lockdep_init_map(&lock->dep_map, name, key, 0);
  89 #endif
  90 }
  91
  92 #define six_lock_init(lock)                                             \
  93 do {                                                                    \
  94         static struct lock_class_key __key;                             \
  95                                                                         \
  96         __six_lock_init((lock), #lock, &__key);                         \
  97 } while (0)
  98
  99 bool six_trylock_type(struct six_lock *, enum six_lock_type);
 100 bool six_relock_type(struct six_lock *, enum six_lock_type, unsigned);
 101 void six_lock_type(struct six_lock *, enum six_lock_type);
 102 void six_unlock_type(struct six_lock *, enum six_lock_type);
 103 bool six_trylock_convert(struct six_lock *, enum six_lock_type,
 104                          enum six_lock_type);
 105 void six_lock_increment(struct six_lock *, enum six_lock_type);
 106 void six_lock_downgrade(struct six_lock *);
 107
 108 #define __SIX_VAL(field, _v)    (((union six_lock_state) { .field = _v }).v)
 109
 110 #define __SIX_LOCK(type)                                                \
 111 static __always_inline bool six_trylock_##type(struct six_lock *lock)   \
 112 {                                                                       \
 113         return six_trylock_type(lock, SIX_LOCK_##type);                 \
 114 }                                                                       \
 115                                                                         \
 116 static __always_inline bool six_relock_##type(struct six_lock *lock, u32 seq)\
 117 {                                                                       \
 118         return six_relock_type(lock, SIX_LOCK_##type, seq);             \
 119 }                                                                       \
 120                                                                         \
 121 static __always_inline void six_lock_##type(struct six_lock *lock)      \
 122 {                                                                       \
 123         six_lock_type(lock, SIX_LOCK_##type);                           \
 124 }                                                                       \
 125                                                                         \
 126 static __always_inline void six_unlock_##type(struct six_lock *lock)    \
 127 {                                                                       \
 128         six_unlock_type(lock, SIX_LOCK_##type);                         \
 129 }
 130
 131 __SIX_LOCK(read)
 132 __SIX_LOCK(intent)
 133 __SIX_LOCK(write)
 134
 135 #endif /* _BCACHEFS_SIX_H */