six locks: Wakeup now takes lock on behalf of waiter
This brings back an important optimization, to avoid touching the wait lists an extra time, while preserving the property that a thread is on a lock waitlist iff it is waiting - it is never removed from the waitlist until it has the lock. Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet
parent
e4b7254c75
commit
84a37cbf62
@ -21,6 +21,8 @@
|
||||
#define six_acquire(l, t, r) lock_acquire(l, 0, t, r, 1, NULL, _RET_IP_)
|
||||
#define six_release(l) lock_release(l, _RET_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;
|
||||
@ -67,14 +69,15 @@ struct six_lock_vals {
|
||||
}
|
||||
|
||||
static inline void six_set_owner(struct six_lock *lock, enum six_lock_type type,
|
||||
union six_lock_state old)
|
||||
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 = current;
|
||||
lock->owner = owner;
|
||||
} else {
|
||||
EBUG_ON(lock->owner != current);
|
||||
}
|
||||
@ -93,47 +96,17 @@ static inline unsigned pcpu_read_count(struct six_lock *lock)
|
||||
/* 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 inline void six_lock_wakeup(struct six_lock *lock,
|
||||
union six_lock_state state,
|
||||
enum six_lock_type lock_type)
|
||||
{
|
||||
struct six_lock_waiter *w;
|
||||
bool found = false;
|
||||
|
||||
if (lock_type == SIX_LOCK_write && state.read_lock)
|
||||
return;
|
||||
|
||||
if (!(state.waiters & (1 << lock_type)))
|
||||
return;
|
||||
|
||||
raw_spin_lock(&lock->wait_lock);
|
||||
|
||||
list_for_each_entry(w, &lock->wait_list, list) {
|
||||
if (w->lock_want != lock_type)
|
||||
continue;
|
||||
|
||||
found = true;
|
||||
wake_up_process(w->task);
|
||||
if (lock_type != SIX_LOCK_read)
|
||||
break;
|
||||
}
|
||||
|
||||
if (!found)
|
||||
clear_bit(waitlist_bitnr(lock_type), (unsigned long *) &lock->state.v);
|
||||
|
||||
raw_spin_unlock(&lock->wait_lock);
|
||||
}
|
||||
|
||||
static __always_inline bool do_six_trylock_type(struct six_lock *lock,
|
||||
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;
|
||||
bool ret;
|
||||
int ret;
|
||||
u64 v;
|
||||
|
||||
EBUG_ON(type == SIX_LOCK_write && lock->owner != current);
|
||||
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)));
|
||||
|
||||
@ -153,7 +126,6 @@ static __always_inline bool do_six_trylock_type(struct six_lock *lock,
|
||||
*/
|
||||
|
||||
if (type == SIX_LOCK_read && lock->readers) {
|
||||
retry:
|
||||
preempt_disable();
|
||||
this_cpu_inc(*lock->readers); /* signal that we own lock */
|
||||
|
||||
@ -171,28 +143,7 @@ retry:
|
||||
* spurious trylock failure:
|
||||
*/
|
||||
if (old.write_locking)
|
||||
six_lock_wakeup(lock, old, SIX_LOCK_write);
|
||||
|
||||
/*
|
||||
* If we failed from the lock path and the waiting bit wasn't
|
||||
* set, set it:
|
||||
*/
|
||||
if (!try && !ret) {
|
||||
v = old.v;
|
||||
|
||||
do {
|
||||
new.v = old.v = v;
|
||||
|
||||
if (!(old.v & l[type].lock_fail))
|
||||
goto retry;
|
||||
|
||||
if (new.waiters & (1 << type))
|
||||
break;
|
||||
|
||||
new.waiters |= 1 << type;
|
||||
} while ((v = atomic64_cmpxchg(&lock->state.counter,
|
||||
old.v, new.v)) != old.v);
|
||||
}
|
||||
ret = -1 - SIX_LOCK_write;
|
||||
} else if (type == SIX_LOCK_write && lock->readers) {
|
||||
if (try) {
|
||||
atomic64_add(__SIX_VAL(write_locking, 1),
|
||||
@ -222,7 +173,8 @@ retry:
|
||||
|
||||
if (try && !ret) {
|
||||
old.v = atomic64_add_return(v, &lock->state.counter);
|
||||
six_lock_wakeup(lock, old, SIX_LOCK_read);
|
||||
if (old.waiters & (1 << SIX_LOCK_read))
|
||||
ret = -1 - SIX_LOCK_read;
|
||||
} else {
|
||||
atomic64_add(v, &lock->state.counter);
|
||||
}
|
||||
@ -248,14 +200,84 @@ retry:
|
||||
EBUG_ON(ret && !(lock->state.v & l[type].held_mask));
|
||||
}
|
||||
|
||||
if (ret)
|
||||
six_set_owner(lock, type, old);
|
||||
if (ret > 0)
|
||||
six_set_owner(lock, type, old, task);
|
||||
|
||||
EBUG_ON(type == SIX_LOCK_write && (try || ret) && (lock->state.write_locking));
|
||||
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)
|
||||
{
|
||||
@ -315,7 +337,7 @@ static bool __six_relock_type(struct six_lock *lock, enum six_lock_type type,
|
||||
old.v,
|
||||
old.v + l[type].lock_val)) != old.v);
|
||||
|
||||
six_set_owner(lock, type, old);
|
||||
six_set_owner(lock, type, old, current);
|
||||
if (type != SIX_LOCK_write)
|
||||
six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read);
|
||||
return true;
|
||||
@ -457,21 +479,24 @@ static int __six_lock_type_slowpath(struct six_lock *lock, enum six_lock_type ty
|
||||
smp_mb__after_atomic();
|
||||
}
|
||||
|
||||
ret = should_sleep_fn ? should_sleep_fn(lock, p) : 0;
|
||||
if (ret)
|
||||
goto out_before_sleep;
|
||||
|
||||
if (six_optimistic_spin(lock, type))
|
||||
goto out_before_sleep;
|
||||
goto out;
|
||||
|
||||
lock_contended(&lock->dep_map, _RET_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)) {
|
||||
@ -484,27 +509,43 @@ static int __six_lock_type_slowpath(struct six_lock *lock, enum six_lock_type ty
|
||||
}
|
||||
|
||||
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 (do_six_trylock_type(lock, type, false))
|
||||
|
||||
if (wait->lock_acquired)
|
||||
break;
|
||||
|
||||
ret = should_sleep_fn ? should_sleep_fn(lock, p) : 0;
|
||||
if (ret)
|
||||
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);
|
||||
|
||||
raw_spin_lock(&lock->wait_lock);
|
||||
list_del(&wait->list);
|
||||
raw_spin_unlock(&lock->wait_lock);
|
||||
out_before_sleep:
|
||||
if (ret && type == SIX_LOCK_write) {
|
||||
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);
|
||||
@ -546,27 +587,13 @@ static int __six_lock_type(struct six_lock *lock, enum six_lock_type type,
|
||||
}
|
||||
|
||||
__always_inline __flatten
|
||||
static void __six_unlock_type(struct six_lock *lock, enum six_lock_type type)
|
||||
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;
|
||||
|
||||
EBUG_ON(type == SIX_LOCK_write &&
|
||||
!(lock->state.v & __SIX_LOCK_HELD_intent));
|
||||
|
||||
if (type != SIX_LOCK_write)
|
||||
six_release(&lock->dep_map);
|
||||
|
||||
if (type == SIX_LOCK_intent) {
|
||||
EBUG_ON(lock->owner != current);
|
||||
|
||||
if (lock->intent_lock_recurse) {
|
||||
--lock->intent_lock_recurse;
|
||||
return;
|
||||
}
|
||||
|
||||
if (type == SIX_LOCK_intent)
|
||||
lock->owner = NULL;
|
||||
}
|
||||
|
||||
if (type == SIX_LOCK_read &&
|
||||
lock->readers) {
|
||||
@ -583,6 +610,27 @@ static void __six_unlock_type(struct six_lock *lock, enum six_lock_type type)
|
||||
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)
|
||||
{
|
||||
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);
|
||||
|
||||
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_##type(struct six_lock *lock) \
|
||||
{ \
|
||||
@ -654,7 +702,7 @@ bool six_lock_tryupgrade(struct six_lock *lock)
|
||||
if (lock->readers)
|
||||
this_cpu_dec(*lock->readers);
|
||||
|
||||
six_set_owner(lock, SIX_LOCK_intent, old);
|
||||
six_set_owner(lock, SIX_LOCK_intent, old, current);
|
||||
|
||||
return true;
|
||||
}
|
||||
@ -713,8 +761,13 @@ 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);
|
||||
|
||||
@ -110,11 +110,10 @@ struct six_lock {
|
||||
union six_lock_state state;
|
||||
unsigned intent_lock_recurse;
|
||||
struct task_struct *owner;
|
||||
unsigned __percpu *readers;
|
||||
#ifdef CONFIG_SIX_LOCK_SPIN_ON_OWNER
|
||||
struct optimistic_spin_queue osq;
|
||||
#endif
|
||||
unsigned __percpu *readers;
|
||||
|
||||
raw_spinlock_t wait_lock;
|
||||
struct list_head wait_list;
|
||||
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
||||
@ -126,6 +125,7 @@ struct six_lock_waiter {
|
||||
struct list_head list;
|
||||
struct task_struct *task;
|
||||
enum six_lock_type lock_want;
|
||||
bool lock_acquired;
|
||||
u64 start_time;
|
||||
};
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user