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 times 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:26;
  84                 unsigned        write_locking:1;
  85                 unsigned        intent_lock:1;
  86                 unsigned        nospin:1;
  87                 unsigned        waiters:3;
  88                 /*
  89                  * seq works much like in seqlocks: it's incremented every time
  90                  * we lock and unlock for write.
  91                  *
  92                  * If it's odd write lock is held, even unlocked.
  93                  *
  94                  * Thus readers can unlock, and then lock again later iff it
  95                  * hasn't been modified in the meantime.
  96                  */
  97                 u32             seq;
  98         };
  99 };
 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         unsigned                intent_lock_recurse;
 110         struct task_struct      *owner;
 111         unsigned __percpu       *readers;
 112         struct optimistic_spin_queue osq;
 113         raw_spinlock_t          wait_lock;
 114         struct list_head        wait_list;
 115 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 116         struct lockdep_map      dep_map;
 117 #endif
 118 };
 119
 120 struct six_lock_waiter {
 121         struct list_head        list;
 122         struct task_struct      *task;
 123         enum six_lock_type      lock_want;
 124         bool                    lock_acquired;
 125         u64                     start_time;
 126 };
 127
 128 typedef int (*six_lock_should_sleep_fn)(struct six_lock *lock, void *);
 129
 130 static __always_inline void __six_lock_init(struct six_lock *lock,
 131                                             const char *name,
 132                                             struct lock_class_key *key)
 133 {
 134         atomic64_set(&lock->state.counter, 0);
 135         raw_spin_lock_init(&lock->wait_lock);
 136         INIT_LIST_HEAD(&lock->wait_list);
 137 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 138         debug_check_no_locks_freed((void *) lock, sizeof(*lock));
 139         lockdep_init_map(&lock->dep_map, name, key, 0);
 140 #endif
 141 }
 142
 143 #define six_lock_init(lock)                                             \
 144 do {                                                                    \
 145         static struct lock_class_key __key;                             \
 146                                                                         \
 147         __six_lock_init((lock), #lock, &__key);                         \
 148 } while (0)
 149
 150 #define __SIX_VAL(field, _v)    (((union six_lock_state) { .field = _v }).v)
 151
 152 #define __SIX_LOCK(type)                                                \
 153 bool six_trylock_ip_##type(struct six_lock *, unsigned long);           \
 154 bool six_relock_ip_##type(struct six_lock *, u32, unsigned long);       \
 155 int six_lock_ip_##type(struct six_lock *, six_lock_should_sleep_fn,     \
 156                        void *, unsigned long);                          \
 157 int six_lock_ip_waiter_##type(struct six_lock *, struct six_lock_waiter *,\
 158                         six_lock_should_sleep_fn, void *, unsigned long);\
 159 void six_unlock_ip_##type(struct six_lock *, unsigned long);            \
 160                                                                         \
 161 static inline bool six_trylock_##type(struct six_lock *lock)            \
 162 {                                                                       \
 163         return six_trylock_ip_##type(lock, _THIS_IP_);                  \
 164 }                                                                       \
 165 static inline bool six_relock_##type(struct six_lock *lock, u32 seq)    \
 166 {                                                                       \
 167         return six_relock_ip_##type(lock, seq, _THIS_IP_);              \
 168 }                                                                       \
 169 static inline int six_lock_##type(struct six_lock *lock,                \
 170                                   six_lock_should_sleep_fn fn, void *p)\
 171 {                                                                       \
 172         return six_lock_ip_##type(lock, fn, p, _THIS_IP_);              \
 173 }                                                                       \
 174 static inline int six_lock_waiter_##type(struct six_lock *lock,         \
 175                         struct six_lock_waiter *wait,                   \
 176                         six_lock_should_sleep_fn fn, void *p)           \
 177 {                                                                       \
 178         return six_lock_ip_waiter_##type(lock, wait, fn, p, _THIS_IP_); \
 179 }                                                                       \
 180 static inline void six_unlock_##type(struct six_lock *lock)             \
 181 {                                                                       \
 182         return six_unlock_ip_##type(lock, _THIS_IP_);                   \
 183 }
 184
 185 __SIX_LOCK(read)
 186 __SIX_LOCK(intent)
 187 __SIX_LOCK(write)
 188 #undef __SIX_LOCK
 189
 190 #define SIX_LOCK_DISPATCH(type, fn, ...)                        \
 191         switch (type) {                                         \
 192         case SIX_LOCK_read:                                     \
 193                 return fn##_read(__VA_ARGS__);                  \
 194         case SIX_LOCK_intent:                                   \
 195                 return fn##_intent(__VA_ARGS__);                \
 196         case SIX_LOCK_write:                                    \
 197                 return fn##_write(__VA_ARGS__);                 \
 198         default:                                                \
 199                 BUG();                                          \
 200         }
 201
 202 static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type)
 203 {
 204         SIX_LOCK_DISPATCH(type, six_trylock, lock);
 205 }
 206
 207 static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type,
 208                                    unsigned seq)
 209 {
 210         SIX_LOCK_DISPATCH(type, six_relock, lock, seq);
 211 }
 212
 213 static inline int six_lock_type(struct six_lock *lock, enum six_lock_type type,
 214                                 six_lock_should_sleep_fn should_sleep_fn, void *p)
 215 {
 216         SIX_LOCK_DISPATCH(type, six_lock, lock, should_sleep_fn, p);
 217 }
 218
 219 static inline int six_lock_type_ip_waiter(struct six_lock *lock, enum six_lock_type type,
 220                                 struct six_lock_waiter *wait,
 221                                 six_lock_should_sleep_fn should_sleep_fn, void *p,
 222                                 unsigned long ip)
 223 {
 224         SIX_LOCK_DISPATCH(type, six_lock_ip_waiter, lock, wait, should_sleep_fn, p, ip);
 225 }
 226
 227 static inline int six_lock_type_waiter(struct six_lock *lock, enum six_lock_type type,
 228                                 struct six_lock_waiter *wait,
 229                                 six_lock_should_sleep_fn should_sleep_fn, void *p)
 230 {
 231         SIX_LOCK_DISPATCH(type, six_lock_waiter, lock, wait, should_sleep_fn, p);
 232 }
 233
 234 static inline void six_unlock_type(struct six_lock *lock, enum six_lock_type type)
 235 {
 236         SIX_LOCK_DISPATCH(type, six_unlock, lock);
 237 }
 238
 239 void six_lock_downgrade(struct six_lock *);
 240 bool six_lock_tryupgrade(struct six_lock *);
 241 bool six_trylock_convert(struct six_lock *, enum six_lock_type,
 242                          enum six_lock_type);
 243
 244 void six_lock_increment(struct six_lock *, enum six_lock_type);
 245
 246 void six_lock_wakeup_all(struct six_lock *);
 247
 248 void six_lock_pcpu_free(struct six_lock *);
 249 void six_lock_pcpu_alloc(struct six_lock *);
 250
 251 struct six_lock_count {
 252         unsigned n[3];
 253 };
 254
 255 struct six_lock_count six_lock_counts(struct six_lock *);
 256
 257 #endif /* _LINUX_SIX_H */