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

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2
   3 #ifndef _LINUX_SIX_H
   4 #define _LINUX_SIX_H
   5
   6 /*
   7  * Shared/intent/exclusive locks: sleepable read/write locks, much like rw
   8  * semaphores, except with a third intermediate state, intent. Basic operations
   9  * are:
  10  *
  11  * six_lock_read(&foo->lock);
  12  * six_unlock_read(&foo->lock);
  13  *
  14  * six_lock_intent(&foo->lock);
  15  * six_unlock_intent(&foo->lock);
  16  *
  17  * six_lock_write(&foo->lock);
  18  * six_unlock_write(&foo->lock);
  19  *
  20  * Intent locks block other intent locks, but do not block read locks, and you
  21  * must have an intent lock held before taking a write lock, like so:
  22  *
  23  * six_lock_intent(&foo->lock);
  24  * six_lock_write(&foo->lock);
  25  * six_unlock_write(&foo->lock);
  26  * six_unlock_intent(&foo->lock);
  27  *
  28  * Other operations:
  29  *
  30  *   six_trylock_read()
  31  *   six_trylock_intent()
  32  *   six_trylock_write()
  33  *
  34  *   six_lock_downgrade():      convert from intent to read
  35  *   six_lock_tryupgrade():     attempt to convert from read to intent
  36  *
  37  * Locks also embed a sequence number, which is incremented when the lock is
  38  * locked or unlocked for write. The current sequence number can be grabbed
  39  * while a lock is held from lock->state.seq; then, if you drop the lock you can
  40  * use six_relock_(read|intent_write)(lock, seq) to attempt to retake the lock
  41  * iff it hasn't been locked for write in the meantime.
  42  *
  43  * There are also operations that take the lock type as a parameter, where the
  44  * type is one of SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write:
  45  *
  46  *   six_lock_type(lock, type)
  47  *   six_unlock_type(lock, type)
  48  *   six_relock(lock, type, seq)
  49  *   six_trylock_type(lock, type)
  50  *   six_trylock_convert(lock, from, to)
  51  *
  52  * A lock may be held multiple types by the same thread (for read or intent,
  53  * not write). However, the six locks code does _not_ implement the actual
  54  * recursive checks itself though - rather, if your code (e.g. btree iterator
  55  * code) knows that the current thread already has a lock held, and for the
  56  * correct type, six_lock_increment() may be used to bump up the counter for
  57  * that type - the only effect is that one more call to unlock will be required
  58  * before the lock is unlocked.
  59  */
  60
  61 #include <linux/lockdep.h>
  62 #include <linux/osq_lock.h>
  63 #include <linux/sched.h>
  64 #include <linux/types.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:28;
  84                 unsigned        intent_lock:1;
  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 enum six_lock_type {
 100         SIX_LOCK_read,
 101         SIX_LOCK_intent,
 102         SIX_LOCK_write,
 103 };
 104
 105 struct six_lock {
 106         union six_lock_state    state;
 107         unsigned                intent_lock_recurse;
 108         struct task_struct      *owner;
 109         struct optimistic_spin_queue osq;
 110
 111         raw_spinlock_t          wait_lock;
 112         struct list_head        wait_list[2];
 113 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 114         struct lockdep_map      dep_map;
 115 #endif
 116 };
 117
 118 typedef int (*six_lock_should_sleep_fn)(struct six_lock *lock, void *);
 119
 120 static __always_inline void __six_lock_init(struct six_lock *lock,
 121                                             const char *name,
 122                                             struct lock_class_key *key)
 123 {
 124         atomic64_set(&lock->state.counter, 0);
 125         raw_spin_lock_init(&lock->wait_lock);
 126         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_read]);
 127         INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_intent]);
 128 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 129         debug_check_no_locks_freed((void *) lock, sizeof(*lock));
 130         lockdep_init_map(&lock->dep_map, name, key, 0);
 131 #endif
 132 }
 133
 134 #define six_lock_init(lock)                                             \
 135 do {                                                                    \
 136         static struct lock_class_key __key;                             \
 137                                                                         \
 138         __six_lock_init((lock), #lock, &__key);                         \
 139 } while (0)
 140
 141 #define __SIX_VAL(field, _v)    (((union six_lock_state) { .field = _v }).v)
 142
 143 #define __SIX_LOCK(type)                                                \
 144 bool six_trylock_##type(struct six_lock *);                             \
 145 bool six_relock_##type(struct six_lock *, u32);                         \
 146 int six_lock_##type(struct six_lock *, six_lock_should_sleep_fn, void *);\
 147 void six_unlock_##type(struct six_lock *);
 148
 149 __SIX_LOCK(read)
 150 __SIX_LOCK(intent)
 151 __SIX_LOCK(write)
 152 #undef __SIX_LOCK
 153
 154 #define SIX_LOCK_DISPATCH(type, fn, ...)                        \
 155         switch (type) {                                         \
 156         case SIX_LOCK_read:                                     \
 157                 return fn##_read(__VA_ARGS__);                  \
 158         case SIX_LOCK_intent:                                   \
 159                 return fn##_intent(__VA_ARGS__);                \
 160         case SIX_LOCK_write:                                    \
 161                 return fn##_write(__VA_ARGS__);                 \
 162         default:                                                \
 163                 BUG();                                          \
 164         }
 165
 166 static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type)
 167 {
 168         SIX_LOCK_DISPATCH(type, six_trylock, lock);
 169 }
 170
 171 static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type,
 172                                    unsigned seq)
 173 {
 174         SIX_LOCK_DISPATCH(type, six_relock, lock, seq);
 175 }
 176
 177 static inline int six_lock_type(struct six_lock *lock, enum six_lock_type type,
 178                                 six_lock_should_sleep_fn should_sleep_fn, void *p)
 179 {
 180         SIX_LOCK_DISPATCH(type, six_lock, lock, should_sleep_fn, p);
 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 void six_lock_downgrade(struct six_lock *);
 189 bool six_lock_tryupgrade(struct six_lock *);
 190 bool six_trylock_convert(struct six_lock *, enum six_lock_type,
 191                          enum six_lock_type);
 192
 193 void six_lock_increment(struct six_lock *, enum six_lock_type);
 194
 195 void six_lock_wakeup_all(struct six_lock *);
 196
 197 #endif /* _LINUX_SIX_H */