// 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/sched/task.h>
#include <linux/slab.h>
#include <trace/events/lock.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);
#define SIX_LOCK_HELD_read_OFFSET 0
#define SIX_LOCK_HELD_read ~(~0U << 26)
#define SIX_LOCK_HELD_intent (1U << 26)
#define SIX_LOCK_HELD_write (1U << 27)
#define SIX_LOCK_WAITING_read (1U << (28 + SIX_LOCK_read))
#define SIX_LOCK_WAITING_write (1U << (28 + SIX_LOCK_write))
#define SIX_LOCK_NOSPIN (1U << 31)
struct six_lock_vals {
/* Value we add to the lock in order to take the lock: */
u32 lock_val;
/* If the lock has this value (used as a mask), taking the lock fails: */
u32 lock_fail;
/* Mask that indicates lock is held for this type: */
u32 held_mask;
/* Waitlist we wakeup when releasing the lock: */
enum six_lock_type unlock_wakeup;
};
static const struct six_lock_vals l[] = {
[SIX_LOCK_read] = {
.lock_val = 1U << SIX_LOCK_HELD_read_OFFSET,
.lock_fail = SIX_LOCK_HELD_write,
.held_mask = SIX_LOCK_HELD_read,
.unlock_wakeup = SIX_LOCK_write,
},
[SIX_LOCK_intent] = {
.lock_val = SIX_LOCK_HELD_intent,
.lock_fail = SIX_LOCK_HELD_intent,
.held_mask = SIX_LOCK_HELD_intent,
.unlock_wakeup = SIX_LOCK_intent,
},
[SIX_LOCK_write] = {
.lock_val = SIX_LOCK_HELD_write,
.lock_fail = SIX_LOCK_HELD_read,
.held_mask = SIX_LOCK_HELD_write,
.unlock_wakeup = SIX_LOCK_read,
},
};
static inline void six_set_bitmask(struct six_lock *lock, u32 mask)
{
if ((atomic_read(&lock->state) & mask) != mask)
atomic_or(mask, &lock->state);
}
static inline void six_clear_bitmask(struct six_lock *lock, u32 mask)
{
if (atomic_read(&lock->state) & mask)
atomic_and(~mask, &lock->state);
}
static inline void six_set_owner(struct six_lock *lock, enum six_lock_type type,
u32 old, struct task_struct *owner)
{
if (type != SIX_LOCK_intent)
return;
if (!(old & SIX_LOCK_HELD_intent)) {
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;
}
/*
* __do_six_trylock() - main trylock routine
*
* Returns 1 on success, 0 on failure
*
* In percpu reader mode, a failed trylock may cause a spurious trylock failure
* for anoter thread taking the competing lock type, and we may havve to do a
* wakeup: when a wakeup is required, we return -1 - wakeup_type.
*/
static int __do_six_trylock(struct six_lock *lock, enum six_lock_type type,
struct task_struct *task, bool try)
{
int ret;
u32 old;
EBUG_ON(type == SIX_LOCK_write && lock->owner != task);
EBUG_ON(type == SIX_LOCK_write &&
(try != !(atomic_read(&lock->state) & SIX_LOCK_HELD_write)));
/*
* 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.
*
* Failure to take the lock may cause a spurious trylock failure in
* another thread, because we temporarily set the lock to indicate that
* we held it. This would be a problem for a thread in six_lock(), when
* they are calling trylock after adding themself to the waitlist and
* prior to sleeping.
*
* Therefore, if we fail to get the lock, and there were waiters of the
* type we conflict with, we will have to issue a wakeup.
*
* Since we may be called under wait_lock (and by the wakeup code
* itself), we return that the wakeup has to be done instead of doing it
* here.
*/
if (type == SIX_LOCK_read && lock->readers) {
preempt_disable();
this_cpu_inc(*lock->readers); /* signal that we own lock */
smp_mb();
old = atomic_read(&lock->state);
ret = !(old & l[type].lock_fail);
this_cpu_sub(*lock->readers, !ret);
preempt_enable();
if (!ret) {
smp_mb();
if (atomic_read(&lock->state) & SIX_LOCK_WAITING_write)
ret = -1 - SIX_LOCK_write;
}
} else if (type == SIX_LOCK_write && lock->readers) {
if (try)
atomic_add(SIX_LOCK_HELD_write, &lock->state);
/*
* Make sure atomic_add happens before pcpu_read_count and
* six_set_bitmask in slow path happens before pcpu_read_count.
*
* Paired with the smp_mb() in read lock fast path (per-cpu mode)
* and the one before atomic_read in read unlock path.
*/
smp_mb();
ret = !pcpu_read_count(lock);
if (try && !ret) {
old = atomic_sub_return(SIX_LOCK_HELD_write, &lock->state);
if (old & SIX_LOCK_WAITING_read)
ret = -1 - SIX_LOCK_read;
}
} else {
old = atomic_read(&lock->state);
do {
ret = !(old & l[type].lock_fail);
if (!ret || (type == SIX_LOCK_write && !try)) {
smp_mb();
break;
}
} while (!atomic_try_cmpxchg_acquire(&lock->state, &old, old + l[type].lock_val));
EBUG_ON(ret && !(atomic_read(&lock->state) & l[type].held_mask));
}
if (ret > 0)
six_set_owner(lock, type, old, task);
EBUG_ON(type == SIX_LOCK_write && try && ret <= 0 &&
(atomic_read(&lock->state) & SIX_LOCK_HELD_write));
return ret;
}
static 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(lock, lock_type, w->task, false);
if (ret <= 0)
goto unlock;
/*
* Similar to percpu_rwsem_wake_function(), we need to guard
* against the wakee noticing w->lock_acquired, returning, and
* then exiting before we do the wakeup:
*/
task = get_task_struct(w->task);
__list_del(w->list.prev, w->list.next);
/*
* The release barrier here ensures the ordering of the
* __list_del before setting w->lock_acquired; @w is on the
* stack of the thread doing the waiting and will be reused
* after it sees w->lock_acquired with no other locking:
* pairs with smp_load_acquire() in six_lock_slowpath()
*/
smp_store_release(&w->lock_acquired, true);
wake_up_process(task);
put_task_struct(task);
}
six_clear_bitmask(lock, SIX_LOCK_WAITING_read << lock_type);
unlock:
raw_spin_unlock(&lock->wait_lock);
if (ret < 0) {
lock_type = -ret - 1;
goto again;
}
}
__always_inline
static void six_lock_wakeup(struct six_lock *lock, u32 state,
enum six_lock_type lock_type)
{
if (lock_type == SIX_LOCK_write && (state & SIX_LOCK_HELD_read))
return;
if (!(state & (SIX_LOCK_WAITING_read << lock_type)))
return;
__six_lock_wakeup(lock, lock_type);
}
__always_inline
static bool do_six_trylock(struct six_lock *lock, enum six_lock_type type, bool try)
{
int ret;
ret = __do_six_trylock(lock, type, current, try);
if (ret < 0)
__six_lock_wakeup(lock, -ret - 1);
return ret > 0;
}
/**
* six_trylock_ip - attempt to take a six lock without blocking
* @lock: lock to take
* @type: SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write
* @ip: ip parameter for lockdep/lockstat, i.e. _THIS_IP_
*
* Return: true on success, false on failure.
*/
bool six_trylock_ip(struct six_lock *lock, enum six_lock_type type, unsigned long ip)
{
if (!do_six_trylock(lock, type, true))
return false;
if (type != SIX_LOCK_write)
six_acquire(&lock->dep_map, 1, type == SIX_LOCK_read, ip);
return true;
}
EXPORT_SYMBOL_GPL(six_trylock_ip);
/**
* six_relock_ip - attempt to re-take a lock that was held previously
* @lock: lock to take
* @type: SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write
* @seq: lock sequence number obtained from six_lock_seq() while lock was
* held previously
* @ip: ip parameter for lockdep/lockstat, i.e. _THIS_IP_
*
* Return: true on success, false on failure.
*/
bool six_relock_ip(struct six_lock *lock, enum six_lock_type type,
unsigned seq, unsigned long ip)
{
if (six_lock_seq(lock) != seq || !six_trylock_ip(lock, type, ip))
return false;
if (six_lock_seq(lock) != seq) {
six_unlock_ip(lock, type, ip);
return false;
}
return true;
}
EXPORT_SYMBOL_GPL(six_relock_ip);
#ifdef CONFIG_BCACHEFS_SIX_OPTIMISTIC_SPIN
static inline bool six_owner_running(struct six_lock *lock)
{
/*
* 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.
*/
rcu_read_lock();
struct task_struct *owner = READ_ONCE(lock->owner);
bool ret = owner ? owner_on_cpu(owner) : !rt_or_dl_task(current);
rcu_read_unlock();
return ret;
}
static inline bool six_optimistic_spin(struct six_lock *lock,
struct six_lock_waiter *wait,
enum six_lock_type type)
{
unsigned loop = 0;
u64 end_time;
if (type == SIX_LOCK_write)
return false;
if (lock->wait_list.next != &wait->list)
return false;
if (atomic_read(&lock->state) & SIX_LOCK_NOSPIN)
return false;
preempt_disable();
end_time = sched_clock() + 10 * NSEC_PER_USEC;
while (!need_resched() && six_owner_running(lock)) {
/*
* Ensures that writes to the waitlist entry happen after we see
* wait->lock_acquired: pairs with the smp_store_release in
* __six_lock_wakeup
*/
if (smp_load_acquire(&wait->lock_acquired)) {
preempt_enable();
return true;
}
if (!(++loop & 0xf) && (time_after64(sched_clock(), end_time))) {
six_set_bitmask(lock, SIX_LOCK_NOSPIN);
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();
}
preempt_enable();
return false;
}
#else /* CONFIG_LOCK_SPIN_ON_OWNER */
static inline bool six_optimistic_spin(struct six_lock *lock,
struct six_lock_waiter *wait,
enum six_lock_type type)
{
return false;
}
#endif
noinline
static int six_lock_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)
{
int ret = 0;
if (type == SIX_LOCK_write) {
EBUG_ON(atomic_read(&lock->state) & SIX_LOCK_HELD_write);
atomic_add(SIX_LOCK_HELD_write, &lock->state);
smp_mb__after_atomic();
}
trace_contention_begin(lock, 0);
lock_contended(&lock->dep_map, ip);
wait->task = current;
wait->lock_want = type;
wait->lock_acquired = false;
raw_spin_lock(&lock->wait_lock);
six_set_bitmask(lock, SIX_LOCK_WAITING_read << type);
/*
* Retry taking the lock after taking waitlist lock, in case we raced
* with an unlock:
*/
ret = __do_six_trylock(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;
}
if (six_optimistic_spin(lock, wait, type))
goto out;
while (1) {
set_current_state(TASK_UNINTERRUPTIBLE);
/*
* Ensures that writes to the waitlist entry happen after we see
* wait->lock_acquired: pairs with the smp_store_release in
* __six_lock_wakeup
*/
if (smp_load_acquire(&wait->lock_acquired))
break;
ret = should_sleep_fn ? should_sleep_fn(lock, p) : 0;
if (unlikely(ret)) {
bool acquired;
/*
* If should_sleep_fn() returns an error, we are
* required to return that error even if we already
* acquired the lock - should_sleep_fn() might have
* modified external state (e.g. when the deadlock cycle
* detector in bcachefs issued a transaction restart)
*/
raw_spin_lock(&lock->wait_lock);
acquired = wait->lock_acquired;
if (!acquired)
list_del(&wait->list);
raw_spin_unlock(&lock->wait_lock);
if (unlikely(acquired))
do_six_unlock_type(lock, type);
break;
}
schedule();
}
__set_current_state(TASK_RUNNING);
out:
if (ret && type == SIX_LOCK_write) {
six_clear_bitmask(lock, SIX_LOCK_HELD_write);
six_lock_wakeup(lock, atomic_read(&lock->state), SIX_LOCK_read);
}
trace_contention_end(lock, 0);
return ret;
}
/**
* six_lock_ip_waiter - take a lock, with full waitlist interface
* @lock: lock to take
* @type: SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write
* @wait: pointer to wait object, which will be added to lock's waitlist
* @should_sleep_fn: callback run after adding to waitlist, immediately prior
* to scheduling
* @p: passed through to @should_sleep_fn
* @ip: ip parameter for lockdep/lockstat, i.e. _THIS_IP_
*
* This is the most general six_lock() variant, with parameters to support full
* cycle detection for deadlock avoidance.
*
* The code calling this function must implement tracking of held locks, and the
* @wait object should be embedded into the struct that tracks held locks -
* which must also be accessible in a thread-safe way.
*
* @should_sleep_fn should invoke the cycle detector; it should walk each
* lock's waiters, and for each waiter recursively walk their held locks.
*
* When this function must block, @wait will be added to @lock's waitlist before
* calling trylock, and before calling @should_sleep_fn, and @wait will not be
* removed from the lock waitlist until the lock has been successfully acquired,
* or we abort.
*
* @wait.start_time will be monotonically increasing for any given waitlist, and
* thus may be used as a loop cursor.
*
* Return: 0 on success, or the return code from @should_sleep_fn on failure.
*/
int six_lock_ip_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(lock, type, true) ? 0
: six_lock_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;
}
EXPORT_SYMBOL_GPL(six_lock_ip_waiter);
__always_inline
static void do_six_unlock_type(struct six_lock *lock, enum six_lock_type type)
{
u32 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 = atomic_read(&lock->state);
} else {
u32 v = l[type].lock_val;
if (type != SIX_LOCK_read)
v += atomic_read(&lock->state) & SIX_LOCK_NOSPIN;
EBUG_ON(!(atomic_read(&lock->state) & l[type].held_mask));
state = atomic_sub_return_release(v, &lock->state);
}
six_lock_wakeup(lock, state, l[type].unlock_wakeup);
}
/**
* six_unlock_ip - drop a six lock
* @lock: lock to unlock
* @type: SIX_LOCK_read, SIX_LOCK_intent, or SIX_LOCK_write
* @ip: ip parameter for lockdep/lockstat, i.e. _THIS_IP_
*
* When a lock is held multiple times (because six_lock_incement()) was used),
* this decrements the 'lock held' counter by one.
*
* For example:
* six_lock_read(&foo->lock); read count 1
* six_lock_increment(&foo->lock, SIX_LOCK_read); read count 2
* six_lock_unlock(&foo->lock, SIX_LOCK_read); read count 1
* six_lock_unlock(&foo->lock, SIX_LOCK_read); read count 0
*/
void six_unlock_ip(struct six_lock *lock, enum six_lock_type type, unsigned long ip)
{
EBUG_ON(type == SIX_LOCK_write &&
!(atomic_read(&lock->state) & 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);
else
lock->seq++;
if (type == SIX_LOCK_intent &&
lock->intent_lock_recurse) {
--lock->intent_lock_recurse;
return;
}
do_six_unlock_type(lock, type);
}
EXPORT_SYMBOL_GPL(six_unlock_ip);
/**
* six_lock_downgrade - convert an intent lock to a read lock
* @lock: lock to dowgrade
*
* @lock will have read count incremented and intent count decremented
*/
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);
/**
* six_lock_tryupgrade - attempt to convert read lock to an intent lock
* @lock: lock to upgrade
*
* On success, @lock will have intent count incremented and read count
* decremented
*
* Return: true on success, false on failure
*/
bool six_lock_tryupgrade(struct six_lock *lock)
{
u32 old = atomic_read(&lock->state), new;
do {
new = old;
if (new & SIX_LOCK_HELD_intent)
return false;
if (!lock->readers) {
EBUG_ON(!(new & SIX_LOCK_HELD_read));
new -= l[SIX_LOCK_read].lock_val;
}
new |= SIX_LOCK_HELD_intent;
} while (!atomic_try_cmpxchg_acquire(&lock->state, &old, new));
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);
/**
* six_trylock_convert - attempt to convert a held lock from one type to another
* @lock: lock to upgrade
* @from: SIX_LOCK_read or SIX_LOCK_intent
* @to: SIX_LOCK_read or SIX_LOCK_intent
*
* On success, @lock will have intent count incremented and read count
* decremented
*
* Return: true on success, false on failure
*/
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);
/**
* six_lock_increment - increase held lock count on a lock that is already held
* @lock: lock to increment
* @type: SIX_LOCK_read or SIX_LOCK_intent
*
* @lock must already be held, with a lock type that is greater than or equal to
* @type
*
* A corresponding six_unlock_type() call will be required for @lock to be fully
* unlocked.
*/
void six_lock_increment(struct six_lock *lock, enum six_lock_type type)
{
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(!(atomic_read(&lock->state) &
(SIX_LOCK_HELD_read|
SIX_LOCK_HELD_intent)));
atomic_add(l[type].lock_val, &lock->state);
}
break;
case SIX_LOCK_intent:
EBUG_ON(!(atomic_read(&lock->state) & SIX_LOCK_HELD_intent));
lock->intent_lock_recurse++;
break;
case SIX_LOCK_write:
BUG();
break;
}
}
EXPORT_SYMBOL_GPL(six_lock_increment);
/**
* six_lock_wakeup_all - wake up all waiters on @lock
* @lock: lock to wake up waiters for
*
* Wakeing up waiters will cause them to re-run should_sleep_fn, which may then
* abort the lock operation.
*
* This function is never needed in a bug-free program; it's only useful in
* debug code, e.g. to determine if a cycle detector is at fault.
*/
void six_lock_wakeup_all(struct six_lock *lock)
{
u32 state = atomic_read(&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);
/**
* six_lock_counts - return held lock counts, for each lock type
* @lock: lock to return counters for
*
* Return: the number of times a lock is held for read, intent and write.
*/
struct six_lock_count six_lock_counts(struct six_lock *lock)
{
struct six_lock_count ret;
ret.n[SIX_LOCK_read] = !lock->readers
? atomic_read(&lock->state) & SIX_LOCK_HELD_read
: pcpu_read_count(lock);
ret.n[SIX_LOCK_intent] = !!(atomic_read(&lock->state) & SIX_LOCK_HELD_intent) +
lock->intent_lock_recurse;
ret.n[SIX_LOCK_write] = !!(atomic_read(&lock->state) & SIX_LOCK_HELD_write);
return ret;
}
EXPORT_SYMBOL_GPL(six_lock_counts);
/**
* six_lock_readers_add - directly manipulate reader count of a lock
* @lock: lock to add/subtract readers for
* @nr: reader count to add/subtract
*
* When an upper layer is implementing lock reentrency, we may have both read
* and intent locks on the same lock.
*
* When we need to take a write lock, the read locks will cause self-deadlock,
* because six locks themselves do not track which read locks are held by the
* current thread and which are held by a different thread - it does no
* per-thread tracking of held locks.
*
* The upper layer that is tracking held locks may however, if trylock() has
* failed, count up its own read locks, subtract them, take the write lock, and
* then re-add them.
*
* As in any other situation when taking a write lock, @lock must be held for
* intent one (or more) times, so @lock will never be left unlocked.
*/
void six_lock_readers_add(struct six_lock *lock, int nr)
{
if (lock->readers) {
this_cpu_add(*lock->readers, nr);
} else {
EBUG_ON((int) (atomic_read(&lock->state) & SIX_LOCK_HELD_read) + nr < 0);
/* reader count starts at bit 0 */
atomic_add(nr, &lock->state);
}
}
EXPORT_SYMBOL_GPL(six_lock_readers_add);
/**
* six_lock_exit - release resources held by a lock prior to freeing
* @lock: lock to exit
*
* When a lock was initialized in percpu mode (SIX_OLCK_INIT_PCPU), this is
* required to free the percpu read counts.
*/
void six_lock_exit(struct six_lock *lock)
{
WARN_ON(lock->readers && pcpu_read_count(lock));
WARN_ON(atomic_read(&lock->state) & SIX_LOCK_HELD_read);
free_percpu(lock->readers);
lock->readers = NULL;
}
EXPORT_SYMBOL_GPL(six_lock_exit);
void __six_lock_init(struct six_lock *lock, const char *name,
struct lock_class_key *key, enum six_lock_init_flags flags)
{
atomic_set(&lock->state, 0);
raw_spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
debug_check_no_locks_freed((void *) lock, sizeof(*lock));
lockdep_init_map(&lock->dep_map, name, key, 0);
#endif
/*
* Don't assume that we have real percpu variables available in
* userspace:
*/
#ifdef __KERNEL__
if (flags & SIX_LOCK_INIT_PCPU) {
/*
* We don't return an error here on memory allocation failure
* since percpu is an optimization, and locks will work with the
* same semantics in non-percpu mode: callers can check for
* failure if they wish by checking lock->readers, but generally
* will not want to treat it as an error.
*/
lock->readers = alloc_percpu(unsigned);
}
#endif
}
EXPORT_SYMBOL_GPL(__six_lock_init);
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