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authorKent Overstreet <kent.overstreet@linux.dev>2022-08-27 02:22:24 +0300
committerKent Overstreet <kent.overstreet@linux.dev>2023-10-23 00:09:41 +0300
commit84a37cbf62e04480607ddd1940e3d8ce65b3828d (patch)
tree1a06e51f22ac15df4105a65d20836aadeab8507d /fs/bcachefs/six.c
parente4b7254c754b676a6f4d607fd92cd71d221ff130 (diff)
downloadlinux-84a37cbf62e04480607ddd1940e3d8ce65b3828d.tar.xz
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>
Diffstat (limited to 'fs/bcachefs/six.c')
-rw-r--r--fs/bcachefs/six.c263
1 files changed, 158 insertions, 105 deletions
diff --git a/fs/bcachefs/six.c b/fs/bcachefs/six.c
index abdc2414f58b..3f9d4ff2edf4 100644
--- a/fs/bcachefs/six.c
+++ b/fs/bcachefs/six.c
@@ -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,
- enum six_lock_type type,
- bool try)
+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;
@@ -457,54 +479,73 @@ 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);
- wait->start_time = local_clock();
+ /*
+ * 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 (!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;
- }
+ 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);
+ 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);