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/sched.h>
  63 #include <linux/types.h>
  64
  65 #define SIX_LOCK_SEPARATE_LOCKFNS
  66
  67 union six_lock_state {
  68         struct {
  69                 atomic64_t      counter;
  70         };
  71
  72         struct {
  73                 u64             v;
  74         };
  75
  76         struct {
  77                 /* for waitlist_bitnr() */
  78                 unsigned long   l;
  79         };
  80
  81         struct {
  82                 unsigned        read_lock:27;
  83                 unsigned        write_locking:1;
  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         struct task_struct      *owner;
 108         unsigned __percpu       *readers;
 109         unsigned                intent_lock_recurse;
 110         unsigned long           ip;
 111         raw_spinlock_t          wait_lock;
 112         struct list_head        wait_list;
 113 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 114         struct lockdep_map      dep_map;
 115 #endif
 116 };
 117
 118 struct six_lock_waiter {
 119         struct list_head        list;
 120         struct task_struct      *task;
 121         enum six_lock_type      lock_want;
 122         bool                    lock_acquired;
 123         u64                     start_time;
 124 };
 125
 126 typedef int (*six_lock_should_sleep_fn)(struct six_lock *lock, void *);
 127
 128 static __always_inline void __six_lock_init(struct six_lock *lock,
 129                                             const char *name,
 130                                             struct lock_class_key *key)
 131 {
 132         atomic64_set(&lock->state.counter, 0);
 133         raw_spin_lock_init(&lock->wait_lock);
 134         INIT_LIST_HEAD(&lock->wait_list);
 135 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 136         debug_check_no_locks_freed((void *) lock, sizeof(*lock));
 137         lockdep_init_map(&lock->dep_map, name, key, 0);
 138 #endif
 139 }
 140
 141 #define six_lock_init(lock)                                             \
 142 do {                                                                    \
 143         static struct lock_class_key __key;                             \
 144                                                                         \
 145         __six_lock_init((lock), #lock, &__key);                         \
 146 } while (0)
 147
 148 #define __SIX_VAL(field, _v)    (((union six_lock_state) { .field = _v }).v)
 149
 150 #define __SIX_LOCK(type)                                                \
 151 bool six_trylock_##type(struct six_lock *);                             \
 152 bool six_relock_##type(struct six_lock *, u32);                         \
 153 int six_lock_##type(struct six_lock *, six_lock_should_sleep_fn, void *);\
 154 int six_lock_waiter_##type(struct six_lock *, struct six_lock_waiter *, \
 155                            six_lock_should_sleep_fn, void *);           \
 156 void six_unlock_##type(struct six_lock *);
 157
 158 __SIX_LOCK(read)
 159 __SIX_LOCK(intent)
 160 __SIX_LOCK(write)
 161 #undef __SIX_LOCK
 162
 163 #define SIX_LOCK_DISPATCH(type, fn, ...)                        \
 164         switch (type) {                                         \
 165         case SIX_LOCK_read:                                     \
 166                 return fn##_read(__VA_ARGS__);                  \
 167         case SIX_LOCK_intent:                                   \
 168                 return fn##_intent(__VA_ARGS__);                \
 169         case SIX_LOCK_write:                                    \
 170                 return fn##_write(__VA_ARGS__);                 \
 171         default:                                                \
 172                 BUG();                                          \
 173         }
 174
 175 static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type)
 176 {
 177         SIX_LOCK_DISPATCH(type, six_trylock, lock);
 178 }
 179
 180 static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type,
 181                                    unsigned seq)
 182 {
 183         SIX_LOCK_DISPATCH(type, six_relock, lock, seq);
 184 }
 185
 186 static inline int six_lock_type(struct six_lock *lock, enum six_lock_type type,
 187                                 six_lock_should_sleep_fn should_sleep_fn, void *p)
 188 {
 189         SIX_LOCK_DISPATCH(type, six_lock, lock, should_sleep_fn, p);
 190 }
 191
 192 static inline int six_lock_type_waiter(struct six_lock *lock, enum six_lock_type type,
 193                                 struct six_lock_waiter *wait,
 194                                 six_lock_should_sleep_fn should_sleep_fn, void *p)
 195 {
 196         SIX_LOCK_DISPATCH(type, six_lock_waiter, lock, wait, should_sleep_fn, p);
 197 }
 198
 199 static inline void six_unlock_type(struct six_lock *lock, enum six_lock_type type)
 200 {
 201         SIX_LOCK_DISPATCH(type, six_unlock, lock);
 202 }
 203
 204 void six_lock_downgrade(struct six_lock *);
 205 bool six_lock_tryupgrade(struct six_lock *);
 206 bool six_trylock_convert(struct six_lock *, enum six_lock_type,
 207                          enum six_lock_type);
 208
 209 void six_lock_increment(struct six_lock *, enum six_lock_type);
 210
 211 void six_lock_wakeup_all(struct six_lock *);
 212
 213 void six_lock_pcpu_free(struct six_lock *);
 214 void six_lock_pcpu_alloc(struct six_lock *);
 215
 216 struct six_lock_count {
 217         unsigned n[3];
 218 };
 219
 220 struct six_lock_count six_lock_counts(struct six_lock *);
 221
 222 #endif /* _LINUX_SIX_H */