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/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_SIX_H
#define _LINUX_SIX_H
/*
* Shared/intent/exclusive locks: sleepable read/write locks, much like rw
* semaphores, except with a third intermediate state, intent. Basic operations
* are:
*
* six_lock_read(&foo->lock);
* six_unlock_read(&foo->lock);
*
* six_lock_intent(&foo->lock);
* six_unlock_intent(&foo->lock);
*
* six_lock_write(&foo->lock);
* six_unlock_write(&foo->lock);
*
* Intent locks block other intent locks, but do not block read locks, and you
* must have an intent lock held before taking a write lock, like so:
*
* six_lock_intent(&foo->lock);
* six_lock_write(&foo->lock);
* six_unlock_write(&foo->lock);
* six_unlock_intent(&foo->lock);
*
* Other operations:
*
* six_trylock_read()
* six_trylock_intent()
* six_trylock_write()
*
* six_lock_downgrade(): convert from intent to read
* six_lock_tryupgrade(): attempt to convert from read to intent
*
* Locks also embed a sequence number, which is incremented when the lock is
* locked or unlocked for write. The current sequence number can be grabbed
* while a lock is held from lock->state.seq; then, if you drop the lock you can
* use six_relock_(read|intent_write)(lock, seq) to attempt to retake the lock
* iff it hasn't been locked for write in the meantime.
*
* There are also operations that take the lock type as a parameter, where the
* type is one of SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write:
*
* six_lock_type(lock, type)
* six_unlock_type(lock, type)
* six_relock(lock, type, seq)
* six_trylock_type(lock, type)
* six_trylock_convert(lock, from, to)
*
* A lock may be held multiple types by the same thread (for read or intent,
* not write). However, the six locks code does _not_ implement the actual
* recursive checks itself though - rather, if your code (e.g. btree iterator
* code) knows that the current thread already has a lock held, and for the
* correct type, six_lock_increment() may be used to bump up the counter for
* that type - the only effect is that one more call to unlock will be required
* before the lock is unlocked.
*/
#include <linux/lockdep.h>
#include <linux/osq_lock.h>
#include <linux/sched.h>
#include <linux/types.h>
#define SIX_LOCK_SEPARATE_LOCKFNS
union six_lock_state {
struct {
atomic64_t counter;
};
struct {
u64 v;
};
struct {
/* for waitlist_bitnr() */
unsigned long l;
};
struct {
unsigned read_lock:28;
unsigned intent_lock:1;
unsigned waiters:3;
/*
* seq works much like in seqlocks: it's incremented every time
* we lock and unlock for write.
*
* If it's odd write lock is held, even unlocked.
*
* Thus readers can unlock, and then lock again later iff it
* hasn't been modified in the meantime.
*/
u32 seq;
};
};
enum six_lock_type {
SIX_LOCK_read,
SIX_LOCK_intent,
SIX_LOCK_write,
};
struct six_lock {
union six_lock_state state;
unsigned intent_lock_recurse;
struct task_struct *owner;
struct optimistic_spin_queue osq;
raw_spinlock_t wait_lock;
struct list_head wait_list[2];
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
};
typedef int (*six_lock_should_sleep_fn)(struct six_lock *lock, void *);
static __always_inline void __six_lock_init(struct six_lock *lock,
const char *name,
struct lock_class_key *key)
{
atomic64_set(&lock->state.counter, 0);
raw_spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_read]);
INIT_LIST_HEAD(&lock->wait_list[SIX_LOCK_intent]);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
debug_check_no_locks_freed((void *) lock, sizeof(*lock));
lockdep_init_map(&lock->dep_map, name, key, 0);
#endif
}
#define six_lock_init(lock) \
do { \
static struct lock_class_key __key; \
\
__six_lock_init((lock), #lock, &__key); \
} while (0)
#define __SIX_VAL(field, _v) (((union six_lock_state) { .field = _v }).v)
#define __SIX_LOCK(type) \
bool six_trylock_##type(struct six_lock *); \
bool six_relock_##type(struct six_lock *, u32); \
int six_lock_##type(struct six_lock *, six_lock_should_sleep_fn, void *);\
void six_unlock_##type(struct six_lock *);
__SIX_LOCK(read)
__SIX_LOCK(intent)
__SIX_LOCK(write)
#undef __SIX_LOCK
#define SIX_LOCK_DISPATCH(type, fn, ...) \
switch (type) { \
case SIX_LOCK_read: \
return fn##_read(__VA_ARGS__); \
case SIX_LOCK_intent: \
return fn##_intent(__VA_ARGS__); \
case SIX_LOCK_write: \
return fn##_write(__VA_ARGS__); \
default: \
BUG(); \
}
static inline bool six_trylock_type(struct six_lock *lock, enum six_lock_type type)
{
SIX_LOCK_DISPATCH(type, six_trylock, lock);
}
static inline bool six_relock_type(struct six_lock *lock, enum six_lock_type type,
unsigned seq)
{
SIX_LOCK_DISPATCH(type, six_relock, lock, seq);
}
static inline int six_lock_type(struct six_lock *lock, enum six_lock_type type,
six_lock_should_sleep_fn should_sleep_fn, void *p)
{
SIX_LOCK_DISPATCH(type, six_lock, lock, should_sleep_fn, p);
}
static inline void six_unlock_type(struct six_lock *lock, enum six_lock_type type)
{
SIX_LOCK_DISPATCH(type, six_unlock, lock);
}
void six_lock_downgrade(struct six_lock *);
bool six_lock_tryupgrade(struct six_lock *);
bool six_trylock_convert(struct six_lock *, enum six_lock_type,
enum six_lock_type);
void six_lock_increment(struct six_lock *, enum six_lock_type);
void six_lock_wakeup_all(struct six_lock *);
#endif /* _LINUX_SIX_H */
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