linux/fs/bcachefs/six.c

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// SPDX-License-Identifier: GPL-2.0
#include <linux/export.h>
#include <linux/log2.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/rcupdate.h>
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/sched/rt.h>
#include <linux/slab.h>
#include "six.h"
#ifdef DEBUG
#define EBUG_ON(cond) BUG_ON(cond)
#else
#define EBUG_ON(cond) do {} while (0)
#endif
#define six_acquire(l, t, r, ip) lock_acquire(l, 0, t, r, 1, NULL, ip)
#define six_release(l, ip) lock_release(l, ip)
static void do_six_unlock_type(struct six_lock *lock, enum six_lock_type type);
struct six_lock_vals {
/* Value we add to the lock in order to take the lock: */
u64 lock_val;
/* If the lock has this value (used as a mask), taking the lock fails: */
u64 lock_fail;
/* Value we add to the lock in order to release the lock: */
u64 unlock_val;
/* Mask that indicates lock is held for this type: */
u64 held_mask;
/* Waitlist we wakeup when releasing the lock: */
enum six_lock_type unlock_wakeup;
};
#define __SIX_LOCK_HELD_read __SIX_VAL(read_lock, ~0)
#define __SIX_LOCK_HELD_intent __SIX_VAL(intent_lock, ~0)
#define __SIX_LOCK_HELD_write __SIX_VAL(seq, 1)
#define LOCK_VALS { \
[SIX_LOCK_read] = { \
.lock_val = __SIX_VAL(read_lock, 1), \
.lock_fail = __SIX_LOCK_HELD_write + __SIX_VAL(write_locking, 1),\
.unlock_val = -__SIX_VAL(read_lock, 1), \
.held_mask = __SIX_LOCK_HELD_read, \
.unlock_wakeup = SIX_LOCK_write, \
}, \
[SIX_LOCK_intent] = { \
.lock_val = __SIX_VAL(intent_lock, 1), \
.lock_fail = __SIX_LOCK_HELD_intent, \
.unlock_val = -__SIX_VAL(intent_lock, 1), \
.held_mask = __SIX_LOCK_HELD_intent, \
.unlock_wakeup = SIX_LOCK_intent, \
}, \
[SIX_LOCK_write] = { \
.lock_val = __SIX_VAL(seq, 1), \
.lock_fail = __SIX_LOCK_HELD_read, \
.unlock_val = __SIX_VAL(seq, 1), \
.held_mask = __SIX_LOCK_HELD_write, \
.unlock_wakeup = SIX_LOCK_read, \
}, \
}
static inline void six_set_owner(struct six_lock *lock, enum six_lock_type type,
union six_lock_state old,
struct task_struct *owner)
{
if (type != SIX_LOCK_intent)
return;
if (!old.intent_lock) {
EBUG_ON(lock->owner);
lock->owner = owner;
} else {
EBUG_ON(lock->owner != current);
}
}
static inline unsigned pcpu_read_count(struct six_lock *lock)
{
unsigned read_count = 0;
int cpu;
for_each_possible_cpu(cpu)
read_count += *per_cpu_ptr(lock->readers, cpu);
return read_count;
}
/* This is probably up there with the more evil things I've done */
#define waitlist_bitnr(id) ilog2((((union six_lock_state) { .waiters = 1 << (id) }).l))
static int __do_six_trylock_type(struct six_lock *lock,
enum six_lock_type type,
struct task_struct *task,
bool try)
{
const struct six_lock_vals l[] = LOCK_VALS;
union six_lock_state old, new;
int ret;
u64 v;
EBUG_ON(type == SIX_LOCK_write && lock->owner != task);
EBUG_ON(type == SIX_LOCK_write && (lock->state.seq & 1));
EBUG_ON(type == SIX_LOCK_write && (try != !(lock->state.write_locking)));
/*
* Percpu reader mode:
*
* The basic idea behind this algorithm is that you can implement a lock
* between two threads without any atomics, just memory barriers:
*
* For two threads you'll need two variables, one variable for "thread a
* has the lock" and another for "thread b has the lock".
*
* To take the lock, a thread sets its variable indicating that it holds
* the lock, then issues a full memory barrier, then reads from the
* other thread's variable to check if the other thread thinks it has
* the lock. If we raced, we backoff and retry/sleep.
*/
if (type == SIX_LOCK_read && lock->readers) {
preempt_disable();
this_cpu_inc(*lock->readers); /* signal that we own lock */
smp_mb();
old.v = READ_ONCE(lock->state.v);
ret = !(old.v & l[type].lock_fail);
this_cpu_sub(*lock->readers, !ret);
preempt_enable();
/*
* If we failed because a writer was trying to take the
* lock, issue a wakeup because we might have caused a
* spurious trylock failure:
*/
if (old.write_locking)
ret = -1 - SIX_LOCK_write;
} else if (type == SIX_LOCK_write && lock->readers) {
if (try) {
atomic64_add(__SIX_VAL(write_locking, 1),
&lock->state.counter);
smp_mb__after_atomic();
} else if (!(lock->state.waiters & (1 << SIX_LOCK_write))) {
atomic64_add(__SIX_VAL(waiters, 1 << SIX_LOCK_write),
&lock->state.counter);
/*
* pairs with barrier after unlock and before checking
* for readers in unlock path
*/
smp_mb__after_atomic();
}
ret = !pcpu_read_count(lock);
/*
* On success, we increment lock->seq; also we clear
* write_locking unless we failed from the lock path:
*/
v = 0;
if (ret)
v += __SIX_VAL(seq, 1);
if (ret || try)
v -= __SIX_VAL(write_locking, 1);
if (try && !ret) {
old.v = atomic64_add_return(v, &lock->state.counter);
if (old.waiters & (1 << SIX_LOCK_read))
ret = -1 - SIX_LOCK_read;
} else {
atomic64_add(v, &lock->state.counter);
}
} else {
v = READ_ONCE(lock->state.v);
do {
new.v = old.v = v;
if (!(old.v & l[type].lock_fail)) {
new.v += l[type].lock_val;
if (type == SIX_LOCK_write)
new.write_locking = 0;
} else if (!try && !(new.waiters & (1 << type)))
new.waiters |= 1 << type;
else
break; /* waiting bit already set */
} while ((v = atomic64_cmpxchg_acquire(&lock->state.counter,
old.v, new.v)) != old.v);
ret = !(old.v & l[type].lock_fail);
EBUG_ON(ret && !(lock->state.v & l[type].held_mask));
}
if (ret > 0)
six_set_owner(lock, type, old, task);
EBUG_ON(type == SIX_LOCK_write && (try || ret > 0) && (lock->state.write_locking));
return ret;
}
static inline void __six_lock_wakeup(struct six_lock *lock, enum six_lock_type lock_type)
{
struct six_lock_waiter *w, *next;
struct task_struct *task;
bool saw_one;
int ret;
again:
ret = 0;
saw_one = false;
raw_spin_lock(&lock->wait_lock);
list_for_each_entry_safe(w, next, &lock->wait_list, list) {
if (w->lock_want != lock_type)
continue;
if (saw_one && lock_type != SIX_LOCK_read)
goto unlock;
saw_one = true;
ret = __do_six_trylock_type(lock, lock_type, w->task, false);
if (ret <= 0)
goto unlock;
__list_del(w->list.prev, w->list.next);
task = w->task;
/*
* Do no writes to @w besides setting lock_acquired - otherwise
* we would need a memory barrier:
*/
barrier();
w->lock_acquired = true;
wake_up_process(task);
}
clear_bit(waitlist_bitnr(lock_type), (unsigned long *) &lock->state.v);
unlock:
raw_spin_unlock(&lock->wait_lock);
if (ret < 0) {
lock_type = -ret - 1;
goto again;
}
}
static inline void six_lock_wakeup(struct six_lock *lock,
union six_lock_state state,
enum six_lock_type lock_type)
{
if (lock_type == SIX_LOCK_write && state.read_lock)
return;
if (!(state.waiters & (1 << lock_type)))
return;
__six_lock_wakeup(lock, lock_type);
}
static bool do_six_trylock_type(struct six_lock *lock,
enum six_lock_type type,
bool try)
{
int ret;
ret = __do_six_trylock_type(lock, type, current, try);
if (ret < 0)
__six_lock_wakeup(lock, -ret - 1);
return ret > 0;
}
__always_inline __flatten
static bool __six_trylock_type(struct six_lock *lock, enum six_lock_type type,
unsigned long ip)
{
if (!do_six_trylock_type(lock, type, true))
return false;
if (type != SIX_LOCK_write)
six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read, ip);
return true;
}
__always_inline __flatten
static bool __six_relock_type(struct six_lock *lock, enum six_lock_type type,
unsigned seq, unsigned long ip)
{
const struct six_lock_vals l[] = LOCK_VALS;
union six_lock_state old;
u64 v;
EBUG_ON(type == SIX_LOCK_write);
if (type == SIX_LOCK_read &&
lock->readers) {
bool ret;
preempt_disable();
this_cpu_inc(*lock->readers);
smp_mb();
old.v = READ_ONCE(lock->state.v);
ret = !(old.v & l[type].lock_fail) && old.seq == seq;
this_cpu_sub(*lock->readers, !ret);
preempt_enable();
/*
* Similar to the lock path, we may have caused a spurious write
* lock fail and need to issue a wakeup:
*/
if (old.write_locking)
six_lock_wakeup(lock, old, SIX_LOCK_write);
if (ret)
six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read, ip);
return ret;
}
v = READ_ONCE(lock->state.v);
do {
old.v = v;
if (old.seq != seq || old.v & l[type].lock_fail)
return false;
} while ((v = atomic64_cmpxchg_acquire(&lock->state.counter,
old.v,
old.v + l[type].lock_val)) != old.v);
six_set_owner(lock, type, old, current);
if (type != SIX_LOCK_write)
six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read, ip);
return true;
}
#ifdef CONFIG_SIX_LOCK_SPIN_ON_OWNER
static inline bool six_can_spin_on_owner(struct six_lock *lock)
{
struct task_struct *owner;
bool ret;
if (need_resched())
return false;
rcu_read_lock();
owner = READ_ONCE(lock->owner);
ret = !owner || owner_on_cpu(owner);
rcu_read_unlock();
return ret;
}
static inline void six_set_nospin(struct six_lock *lock)
{
union six_lock_state old, new;
u64 v = READ_ONCE(lock->state.v);
do {
new.v = old.v = v;
new.nospin = true;
} while ((v = atomic64_cmpxchg(&lock->state.counter, old.v, new.v)) != old.v);
}
static inline bool six_spin_on_owner(struct six_lock *lock,
struct task_struct *owner,
u64 end_time)
{
bool ret = true;
unsigned loop = 0;
rcu_read_lock();
while (lock->owner == owner) {
/*
* Ensure we emit the owner->on_cpu, dereference _after_
* checking lock->owner still matches owner. If that fails,
* owner might point to freed memory. If it still matches,
* the rcu_read_lock() ensures the memory stays valid.
*/
barrier();
if (!owner_on_cpu(owner) || need_resched()) {
ret = false;
break;
}
if (!(++loop & 0xf) && (time_after64(sched_clock(), end_time))) {
six_set_nospin(lock);
ret = false;
break;
}
cpu_relax();
}
rcu_read_unlock();
return ret;
}
static inline bool six_optimistic_spin(struct six_lock *lock, enum six_lock_type type)
{
struct task_struct *task = current;
u64 end_time;
if (type == SIX_LOCK_write)
return false;
preempt_disable();
if (!six_can_spin_on_owner(lock))
goto fail;
if (!osq_lock(&lock->osq))
goto fail;
end_time = sched_clock() + 10 * NSEC_PER_USEC;
while (1) {
struct task_struct *owner;
/*
* If there's an owner, wait for it to either
* release the lock or go to sleep.
*/
owner = READ_ONCE(lock->owner);
if (owner && !six_spin_on_owner(lock, owner, end_time))
break;
if (do_six_trylock_type(lock, type, false)) {
osq_unlock(&lock->osq);
preempt_enable();
return true;
}
/*
* When there's no owner, we might have preempted between the
* owner acquiring the lock and setting the owner field. If
* we're an RT task that will live-lock because we won't let
* the owner complete.
*/
if (!owner && (need_resched() || rt_task(task)))
break;
/*
* The cpu_relax() call is a compiler barrier which forces
* everything in this loop to be re-loaded. We don't need
* memory barriers as we'll eventually observe the right
* values at the cost of a few extra spins.
*/
cpu_relax();
}
osq_unlock(&lock->osq);
fail:
preempt_enable();
/*
* If we fell out of the spin path because of need_resched(),
* reschedule now, before we try-lock again. This avoids getting
* scheduled out right after we obtained the lock.
*/
if (need_resched())
schedule();
return false;
}
#else /* CONFIG_SIX_LOCK_SPIN_ON_OWNER */
static inline bool six_optimistic_spin(struct six_lock *lock, enum six_lock_type type)
{
return false;
}
#endif
noinline
static int __six_lock_type_slowpath(struct six_lock *lock, enum six_lock_type type,
struct six_lock_waiter *wait,
six_lock_should_sleep_fn should_sleep_fn, void *p,
unsigned long ip)
{
union six_lock_state old;
int ret = 0;
if (type == SIX_LOCK_write) {
EBUG_ON(lock->state.write_locking);
atomic64_add(__SIX_VAL(write_locking, 1), &lock->state.counter);
smp_mb__after_atomic();
}
if (six_optimistic_spin(lock, type))
goto out;
lock_contended(&lock->dep_map, ip);
wait->task = current;
wait->lock_want = type;
wait->lock_acquired = false;
raw_spin_lock(&lock->wait_lock);
if (!(lock->state.waiters & (1 << type)))
set_bit(waitlist_bitnr(type), (unsigned long *) &lock->state.v);
/*
* Retry taking the lock after taking waitlist lock, have raced with an
* unlock:
*/
ret = __do_six_trylock_type(lock, type, current, false);
if (ret <= 0) {
wait->start_time = local_clock();
if (!list_empty(&lock->wait_list)) {
struct six_lock_waiter *last =
list_last_entry(&lock->wait_list,
struct six_lock_waiter, list);
if (time_before_eq64(wait->start_time, last->start_time))
wait->start_time = last->start_time + 1;
}
list_add_tail(&wait->list, &lock->wait_list);
}
raw_spin_unlock(&lock->wait_lock);
if (unlikely(ret > 0)) {
ret = 0;
goto out;
}
if (unlikely(ret < 0)) {
__six_lock_wakeup(lock, -ret - 1);
ret = 0;
}
while (1) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (wait->lock_acquired)
break;
ret = should_sleep_fn ? should_sleep_fn(lock, p) : 0;
if (unlikely(ret)) {
raw_spin_lock(&lock->wait_lock);
if (!wait->lock_acquired)
list_del(&wait->list);
raw_spin_unlock(&lock->wait_lock);
if (wait->lock_acquired)
do_six_unlock_type(lock, type);
break;
}
schedule();
}
__set_current_state(TASK_RUNNING);
out:
if (ret && type == SIX_LOCK_write && lock->state.write_locking) {
old.v = atomic64_sub_return(__SIX_VAL(write_locking, 1),
&lock->state.counter);
six_lock_wakeup(lock, old, SIX_LOCK_read);
}
return ret;
}
__always_inline __flatten
static int __six_lock_type_waiter(struct six_lock *lock, enum six_lock_type type,
struct six_lock_waiter *wait,
six_lock_should_sleep_fn should_sleep_fn, void *p,
unsigned long ip)
{
int ret;
wait->start_time = 0;
if (type != SIX_LOCK_write)
six_acquire(&lock->dep_map, 0, type == SIX_LOCK_read, ip);
ret = do_six_trylock_type(lock, type, true) ? 0
: __six_lock_type_slowpath(lock, type, wait, should_sleep_fn, p, ip);
if (ret && type != SIX_LOCK_write)
six_release(&lock->dep_map, ip);
if (!ret)
lock_acquired(&lock->dep_map, ip);
return ret;
}
__always_inline
static int __six_lock_type(struct six_lock *lock, enum six_lock_type type,
six_lock_should_sleep_fn should_sleep_fn, void *p,
unsigned long ip)
{
struct six_lock_waiter wait;
return __six_lock_type_waiter(lock, type, &wait, should_sleep_fn, p, ip);
}
__always_inline __flatten
static void do_six_unlock_type(struct six_lock *lock, enum six_lock_type type)
{
const struct six_lock_vals l[] = LOCK_VALS;
union six_lock_state state;
if (type == SIX_LOCK_intent)
lock->owner = NULL;
if (type == SIX_LOCK_read &&
lock->readers) {
smp_mb(); /* unlock barrier */
this_cpu_dec(*lock->readers);
smp_mb(); /* between unlocking and checking for waiters */
state.v = READ_ONCE(lock->state.v);
} else {
u64 v = l[type].unlock_val;
if (type != SIX_LOCK_read)
v -= lock->state.v & __SIX_VAL(nospin, 1);
EBUG_ON(!(lock->state.v & l[type].held_mask));
state.v = atomic64_add_return_release(v, &lock->state.counter);
}
six_lock_wakeup(lock, state, l[type].unlock_wakeup);
}
__always_inline __flatten
static void __six_unlock_type(struct six_lock *lock, enum six_lock_type type,
unsigned long ip)
{
EBUG_ON(type == SIX_LOCK_write &&
!(lock->state.v & __SIX_LOCK_HELD_intent));
EBUG_ON((type == SIX_LOCK_write ||
type == SIX_LOCK_intent) &&
lock->owner != current);
if (type != SIX_LOCK_write)
six_release(&lock->dep_map, ip);
if (type == SIX_LOCK_intent &&
lock->intent_lock_recurse) {
--lock->intent_lock_recurse;
return;
}
do_six_unlock_type(lock, type);
}
#define __SIX_LOCK(type) \
bool six_trylock_ip_##type(struct six_lock *lock, unsigned long ip) \
{ \
return __six_trylock_type(lock, SIX_LOCK_##type, ip); \
} \
EXPORT_SYMBOL_GPL(six_trylock_ip_##type); \
\
bool six_relock_ip_##type(struct six_lock *lock, u32 seq, unsigned long ip)\
{ \
return __six_relock_type(lock, SIX_LOCK_##type, seq, ip); \
} \
EXPORT_SYMBOL_GPL(six_relock_ip_##type); \
\
int six_lock_ip_##type(struct six_lock *lock, \
six_lock_should_sleep_fn should_sleep_fn, void *p, \
unsigned long ip) \
{ \
return __six_lock_type(lock, SIX_LOCK_##type, should_sleep_fn, p, ip);\
} \
EXPORT_SYMBOL_GPL(six_lock_ip_##type); \
\
int six_lock_ip_waiter_##type(struct six_lock *lock, \
struct six_lock_waiter *wait, \
six_lock_should_sleep_fn should_sleep_fn, void *p,\
unsigned long ip) \
{ \
return __six_lock_type_waiter(lock, SIX_LOCK_##type, wait, should_sleep_fn, p, ip);\
} \
EXPORT_SYMBOL_GPL(six_lock_ip_waiter_##type); \
\
void six_unlock_ip_##type(struct six_lock *lock, unsigned long ip) \
{ \
__six_unlock_type(lock, SIX_LOCK_##type, ip); \
} \
EXPORT_SYMBOL_GPL(six_unlock_ip_##type);
__SIX_LOCK(read)
__SIX_LOCK(intent)
__SIX_LOCK(write)
#undef __SIX_LOCK
/* Convert from intent to read: */
void six_lock_downgrade(struct six_lock *lock)
{
six_lock_increment(lock, SIX_LOCK_read);
six_unlock_intent(lock);
}
EXPORT_SYMBOL_GPL(six_lock_downgrade);
bool six_lock_tryupgrade(struct six_lock *lock)
{
union six_lock_state old, new;
u64 v = READ_ONCE(lock->state.v);
do {
new.v = old.v = v;
if (new.intent_lock)
return false;
if (!lock->readers) {
EBUG_ON(!new.read_lock);
new.read_lock--;
}
new.intent_lock = 1;
} while ((v = atomic64_cmpxchg_acquire(&lock->state.counter,
old.v, new.v)) != old.v);
if (lock->readers)
this_cpu_dec(*lock->readers);
six_set_owner(lock, SIX_LOCK_intent, old, current);
return true;
}
EXPORT_SYMBOL_GPL(six_lock_tryupgrade);
bool six_trylock_convert(struct six_lock *lock,
enum six_lock_type from,
enum six_lock_type to)
{
EBUG_ON(to == SIX_LOCK_write || from == SIX_LOCK_write);
if (to == from)
return true;
if (to == SIX_LOCK_read) {
six_lock_downgrade(lock);
return true;
} else {
return six_lock_tryupgrade(lock);
}
}
EXPORT_SYMBOL_GPL(six_trylock_convert);
/*
* Increment read/intent lock count, assuming we already have it read or intent
* locked:
*/
void six_lock_increment(struct six_lock *lock, enum six_lock_type type)
{
const struct six_lock_vals l[] = LOCK_VALS;
six_acquire(&lock->dep_map, 0, type == SIX_LOCK_read, _RET_IP_);
/* XXX: assert already locked, and that we don't overflow: */
switch (type) {
case SIX_LOCK_read:
if (lock->readers) {
this_cpu_inc(*lock->readers);
} else {
EBUG_ON(!lock->state.read_lock &&
!lock->state.intent_lock);
atomic64_add(l[type].lock_val, &lock->state.counter);
}
break;
case SIX_LOCK_intent:
EBUG_ON(!lock->state.intent_lock);
lock->intent_lock_recurse++;
break;
case SIX_LOCK_write:
BUG();
break;
}
}
EXPORT_SYMBOL_GPL(six_lock_increment);
void six_lock_wakeup_all(struct six_lock *lock)
{
union six_lock_state state = lock->state;
struct six_lock_waiter *w;
six_lock_wakeup(lock, state, SIX_LOCK_read);
six_lock_wakeup(lock, state, SIX_LOCK_intent);
six_lock_wakeup(lock, state, SIX_LOCK_write);
raw_spin_lock(&lock->wait_lock);
list_for_each_entry(w, &lock->wait_list, list)
wake_up_process(w->task);
raw_spin_unlock(&lock->wait_lock);
}
EXPORT_SYMBOL_GPL(six_lock_wakeup_all);
void six_lock_pcpu_free(struct six_lock *lock)
{
BUG_ON(lock->readers && pcpu_read_count(lock));
BUG_ON(lock->state.read_lock);
free_percpu(lock->readers);
lock->readers = NULL;
}
EXPORT_SYMBOL_GPL(six_lock_pcpu_free);
void six_lock_pcpu_alloc(struct six_lock *lock)
{
#ifdef __KERNEL__
if (!lock->readers)
lock->readers = alloc_percpu(unsigned);
#endif
}
EXPORT_SYMBOL_GPL(six_lock_pcpu_alloc);
/*
* Returns lock held counts, for both read and intent
*/
struct six_lock_count six_lock_counts(struct six_lock *lock)
{
struct six_lock_count ret;
ret.n[SIX_LOCK_read] = !lock->readers
? lock->state.read_lock
: pcpu_read_count(lock);
ret.n[SIX_LOCK_intent] = lock->state.intent_lock + lock->intent_lock_recurse;
ret.n[SIX_LOCK_write] = lock->state.seq & 1;
return ret;
}
EXPORT_SYMBOL_GPL(six_lock_counts);