void
lock_set_spl_spin(lock_t *lp, int new_pil, ushort_t *old_pil_addr, int old_pil)
{
int spin_count = 1;
int backoff; /* current backoff */
int backctr; /* ctr for backoff */
if (panicstr)
return;
if (ncpus == 1)
panic("lock_set_spl: %p lock held and only one CPU", lp);
ASSERT(new_pil > LOCK_LEVEL);
if (&plat_lock_delay) {
backoff = 0;
} else {
backoff = BACKOFF_BASE;
}
do {
splx(old_pil);
while (LOCK_HELD(lp)) {
if (panicstr) {
*old_pil_addr = (ushort_t)splr(new_pil);
return;
}
spin_count++;
/*
* Add an exponential backoff delay before trying again
* to touch the mutex data structure.
* spin_count test and call to nulldev are to prevent
* compiler optimizer from eliminating the delay loop.
*/
if (&plat_lock_delay) {
plat_lock_delay(&backoff);
} else {
for (backctr = backoff; backctr; backctr--) {
if (!spin_count) (void) nulldev();
}
backoff = backoff << 1; /* double it */
if (backoff > BACKOFF_CAP) {
backoff = BACKOFF_CAP;
}
SMT_PAUSE();
}
}
old_pil = splr(new_pil);
} while (!lock_spin_try(lp));
*old_pil_addr = (ushort_t)old_pil;
if (spin_count) {
LOCKSTAT_RECORD(LS_LOCK_SET_SPL_SPIN, lp, spin_count);
}
LOCKSTAT_RECORD(LS_LOCK_SET_SPL_ACQUIRE, lp, spin_count);
}
/*
* Routine: lck_mtx_lock_spinwait
*
* Invoked trying to acquire a mutex when there is contention but
* the holder is running on another processor. We spin for up to a maximum
* time waiting for the lock to be released.
*
* Called with the interlock unlocked.
*/
void
lck_mtx_lock_spinwait(
lck_mtx_t *lck)
{
thread_t holder;
volatile lck_mtx_t *mutex;
uint64_t deadline;
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT)
mutex = lck;
else
mutex = &lck->lck_mtx_ptr->lck_mtx;
KERNEL_DEBUG(
MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_SPIN) | DBG_FUNC_NONE,
(int)lck, (int)mutex->lck_mtx_locked, 0, 0, 0);
deadline = mach_absolute_time() + MutexSpin;
/*
* Spin while:
* - mutex is locked, and
* - its locked as a spin lock, or
* - owner is running on another processor, and
* - owner (processor) is not idling, and
* - we haven't spun for long enough.
*/
while ((holder = (thread_t) mutex->lck_mtx_locked) != NULL) {
if ((holder == (thread_t)MUTEX_LOCKED_AS_SPIN) ||
((holder->machine.specFlags & OnProc) != 0 &&
(holder->state & TH_IDLE) == 0 &&
mach_absolute_time() < deadline)) {
cpu_pause();
continue;
}
break;
}
#if CONFIG_DTRACE
/*
* We've already kept a count via deadline of how long we spun.
* If dtrace is active, then we compute backwards to decide how
* long we spun.
*
* Note that we record a different probe id depending on whether
* this is a direct or indirect mutex. This allows us to
* penalize only lock groups that have debug/stats enabled
* with dtrace processing if desired.
*/
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT) {
LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_SPIN, lck,
mach_absolute_time() - (deadline - MutexSpin));
} else {
LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_SPIN, lck,
mach_absolute_time() - (deadline - MutexSpin));
}
/* The lockstat acquire event is recorded by the assembly code beneath us. */
#endif
}
/*
* Routine: lck_mtx_lock_acquire
*
* Invoked on acquiring the mutex when there is
* contention.
*
* Returns the current number of waiters.
*
* Called with the interlock locked.
*/
int
lck_mtx_lock_acquire(
lck_mtx_t *lck)
{
thread_t thread = current_thread();
lck_mtx_t *mutex;
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT)
mutex = lck;
else
mutex = &lck->lck_mtx_ptr->lck_mtx;
if (thread->pending_promoter[thread->pending_promoter_index] == mutex) {
thread->pending_promoter[thread->pending_promoter_index] = NULL;
if (thread->pending_promoter_index > 0)
thread->pending_promoter_index--;
mutex->lck_mtx_waiters--;
}
if (mutex->lck_mtx_waiters > 0) {
integer_t priority = mutex->lck_mtx_pri;
spl_t s = splsched();
thread_lock(thread);
thread->promotions++;
thread->sched_flags |= TH_SFLAG_PROMOTED;
if (thread->sched_pri < priority) {
KERNEL_DEBUG_CONSTANT(
MACHDBG_CODE(DBG_MACH_SCHED,MACH_PROMOTE) | DBG_FUNC_NONE,
thread->sched_pri, priority, 0, lck, 0);
/* Do not promote past promotion ceiling */
assert(priority <= MAXPRI_PROMOTE);
set_sched_pri(thread, priority);
}
thread_unlock(thread);
splx(s);
}
else
mutex->lck_mtx_pri = 0;
#if CONFIG_DTRACE
if (lockstat_probemap[LS_LCK_MTX_LOCK_ACQUIRE] || lockstat_probemap[LS_LCK_MTX_EXT_LOCK_ACQUIRE]) {
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT) {
LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_ACQUIRE, lck, 0);
} else {
LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_ACQUIRE, lck, 0);
}
}
#endif
return (mutex->lck_mtx_waiters);
}
/*
* Routine: hw_lock_lock
*
* Acquire lock, spinning until it becomes available,
* return with preemption disabled.
*/
void
hw_lock_lock(hw_lock_t lock)
{
thread_t thread;
uintptr_t state;
thread = current_thread();
disable_preemption_for_thread(thread);
state = LCK_MTX_THREAD_TO_STATE(thread) | PLATFORM_LCK_ILOCK;
#if __SMP__
#if LOCK_PRETEST
if (ordered_load_hw(lock))
goto contended;
#endif // LOCK_PRETEST
if (atomic_compare_exchange(&lock->lock_data, 0, state,
memory_order_acquire_smp, TRUE)) {
goto end;
}
#if LOCK_PRETEST
contended:
#endif // LOCK_PRETEST
hw_lock_lock_contended(lock, state, 0, TRUE);
end:
#else // __SMP__
if (lock->lock_data)
panic("Spinlock held %p", lock);
lock->lock_data = state;
#endif // __SMP__
#if CONFIG_DTRACE
LOCKSTAT_RECORD(LS_LCK_SPIN_LOCK_ACQUIRE, lock, 0);
#endif
return;
}
boolean_t
lck_rw_try_lock_exclusive(
lck_rw_t *lck)
{
boolean_t istate;
istate = lck_interlock_lock(lck);
if (lck->lck_rw_want_write || lck->lck_rw_want_upgrade || lck->lck_rw_shared_count) {
/*
* Can't get lock.
*/
lck_interlock_unlock(lck, istate);
return(FALSE);
}
/*
* Have lock.
*/
lck->lck_rw_want_write = TRUE;
lck_interlock_unlock(lck, istate);
#if CONFIG_DTRACE
LOCKSTAT_RECORD(LS_LCK_RW_TRY_LOCK_EXCL_ACQUIRE, lck, 1);
#endif
return(TRUE);
}
/*
* Routine: lck_rw_done_gen
*/
lck_rw_type_t
lck_rw_done_gen(
lck_rw_t *lck)
{
boolean_t wakeup_readers = FALSE;
boolean_t wakeup_writers = FALSE;
lck_rw_type_t lck_rw_type;
boolean_t istate;
istate = lck_interlock_lock(lck);
if (lck->lck_rw_shared_count != 0) {
lck_rw_type = LCK_RW_TYPE_SHARED;
lck->lck_rw_shared_count--;
}
else {
lck_rw_type = LCK_RW_TYPE_EXCLUSIVE;
if (lck->lck_rw_want_upgrade)
lck->lck_rw_want_upgrade = FALSE;
else
lck->lck_rw_want_write = FALSE;
}
/*
* There is no reason to wakeup a waiting thread
* if the read-count is non-zero. Consider:
* we must be dropping a read lock
* threads are waiting only if one wants a write lock
* if there are still readers, they can't proceed
*/
if (lck->lck_rw_shared_count == 0) {
if (lck->lck_w_waiting) {
lck->lck_w_waiting = FALSE;
wakeup_writers = TRUE;
}
if (!(lck->lck_rw_priv_excl && wakeup_writers == TRUE) &&
lck->lck_r_waiting) {
lck->lck_r_waiting = FALSE;
wakeup_readers = TRUE;
}
}
lck_interlock_unlock(lck, istate);
if (wakeup_readers)
thread_wakeup(RW_LOCK_READER_EVENT(lck));
if (wakeup_writers)
thread_wakeup(RW_LOCK_WRITER_EVENT(lck));
#if CONFIG_DTRACE
LOCKSTAT_RECORD(LS_LCK_RW_DONE_RELEASE, lck, (lck_rw_type == LCK_RW_TYPE_EXCLUSIVE ? 1 : 0));
#endif
return(lck_rw_type);
}
/*
* Routine: hw_lock_unlock
*
* Unconditionally release lock, release preemption level.
*/
void
hw_lock_unlock(hw_lock_t lock)
{
__c11_atomic_store((_Atomic uintptr_t *)&lock->lock_data, 0, memory_order_release_smp);
#if __arm__ || __arm64__
// ARM tests are only for open-source exclusion
set_event();
#endif // __arm__ || __arm64__
#if CONFIG_DTRACE
LOCKSTAT_RECORD(LS_LCK_SPIN_UNLOCK_RELEASE, lock, 0);
#endif /* CONFIG_DTRACE */
enable_preemption();
}
/*
* Simple C support for the cases where spin locks miss on the first try.
*/
void
lock_set_spin(lock_t *lp)
{
int spin_count = 1;
int backoff; /* current backoff */
int backctr; /* ctr for backoff */
if (panicstr)
return;
if (ncpus == 1)
panic("lock_set: %p lock held and only one CPU", lp);
if (&plat_lock_delay) {
backoff = 0;
} else {
backoff = BACKOFF_BASE;
}
while (LOCK_HELD(lp) || !lock_spin_try(lp)) {
if (panicstr)
return;
spin_count++;
/*
* Add an exponential backoff delay before trying again
* to touch the mutex data structure.
* the spin_count test and call to nulldev are to prevent
* the compiler optimizer from eliminating the delay loop.
*/
if (&plat_lock_delay) {
plat_lock_delay(&backoff);
} else {
/* delay */
for (backctr = backoff; backctr; backctr--) {
if (!spin_count) (void) nulldev();
}
backoff = backoff << 1; /* double it */
if (backoff > BACKOFF_CAP) {
backoff = BACKOFF_CAP;
}
SMT_PAUSE();
}
}
if (spin_count) {
LOCKSTAT_RECORD(LS_LOCK_SET_SPIN, lp, spin_count);
}
LOCKSTAT_RECORD0(LS_LOCK_SET_ACQUIRE, lp);
}
void
lck_mtx_unlockspin_wakeup (
lck_mtx_t *lck)
{
assert(lck->lck_mtx_waiters > 0);
thread_wakeup_one(LCK_MTX_EVENT(lck));
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_UNLCK_WAKEUP_CODE) | DBG_FUNC_NONE, VM_KERNEL_UNSLIDE_OR_PERM(lck), 0, 0, 1, 0);
#if CONFIG_DTRACE
/*
* When there are waiters, we skip the hot-patch spot in the
* fastpath, so we record it here.
*/
LOCKSTAT_RECORD(LS_LCK_MTX_UNLOCK_RELEASE, lck, 0);
#endif
}
void
lck_mtx_unlockspin_wakeup (
lck_mtx_t *lck)
{
assert(lck->lck_mtx_waiters > 0);
thread_wakeup_one((event_t)(((unsigned int*)lck)+(sizeof(lck_mtx_t)-1)/sizeof(unsigned int)));
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_UNLCK_WAKEUP_CODE) | DBG_FUNC_NONE, (int)lck, 0, 0, 1, 0);
#if CONFIG_DTRACE
/*
* When there are waiters, we skip the hot-patch spot in the
* fastpath, so we record it here.
*/
LOCKSTAT_RECORD(LS_LCK_MTX_UNLOCK_RELEASE, lck, 0);
#endif
}
/*
* Routine: hw_lock_try
*
* returns with preemption disabled on success.
*/
unsigned int
hw_lock_try(hw_lock_t lock)
{
thread_t thread = current_thread();
int success = 0;
#if LOCK_TRY_DISABLE_INT
long intmask;
intmask = disable_interrupts();
#else
disable_preemption_for_thread(thread);
#endif // LOCK_TRY_DISABLE_INT
#if __SMP__
#if LOCK_PRETEST
if (ordered_load_hw(lock))
goto failed;
#endif // LOCK_PRETEST
success = atomic_compare_exchange(&lock->lock_data, 0, LCK_MTX_THREAD_TO_STATE(thread) | PLATFORM_LCK_ILOCK,
memory_order_acquire_smp, FALSE);
#else
if (lock->lock_data == 0) {
lock->lock_data = LCK_MTX_THREAD_TO_STATE(thread) | PLATFORM_LCK_ILOCK;
success = 1;
}
#endif // __SMP__
#if LOCK_TRY_DISABLE_INT
if (success)
disable_preemption_for_thread(thread);
#if LOCK_PRETEST
failed:
#endif // LOCK_PRETEST
restore_interrupts(intmask);
#else
#if LOCK_PRETEST
failed:
#endif // LOCK_PRETEST
if (!success)
enable_preemption();
#endif // LOCK_TRY_DISABLE_INT
#if CONFIG_DTRACE
if (success)
LOCKSTAT_RECORD(LS_LCK_SPIN_LOCK_ACQUIRE, lock, 0);
#endif
return success;
}
/*
* Routine: lck_rw_lock_exclusive_to_shared
*/
void
lck_rw_lock_exclusive_to_shared(
lck_rw_t *lck)
{
boolean_t wakeup_readers = FALSE;
boolean_t wakeup_writers = FALSE;
boolean_t istate;
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_TO_SH_CODE) | DBG_FUNC_START,
(int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, 0, 0);
istate = lck_interlock_lock(lck);
lck->lck_rw_shared_count++;
if (lck->lck_rw_want_upgrade)
lck->lck_rw_want_upgrade = FALSE;
else
lck->lck_rw_want_write = FALSE;
if (lck->lck_w_waiting) {
lck->lck_w_waiting = FALSE;
wakeup_writers = TRUE;
}
if (!(lck->lck_rw_priv_excl && wakeup_writers == TRUE) &&
lck->lck_r_waiting) {
lck->lck_r_waiting = FALSE;
wakeup_readers = TRUE;
}
lck_interlock_unlock(lck, istate);
if (wakeup_readers)
thread_wakeup(RW_LOCK_READER_EVENT(lck));
if (wakeup_writers)
thread_wakeup(RW_LOCK_WRITER_EVENT(lck));
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_TO_SH_CODE) | DBG_FUNC_END,
(int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, lck->lck_rw_shared_count, 0);
#if CONFIG_DTRACE
LOCKSTAT_RECORD(LS_LCK_RW_LOCK_EXCL_TO_SHARED_DOWNGRADE, lck, 0);
#endif
}
/*
* Routine: hw_lock_to
*
* Acquire lock, spinning until it becomes available or timeout.
* Timeout is in mach_absolute_time ticks, return with
* preemption disabled.
*/
unsigned int
hw_lock_to(hw_lock_t lock, uint64_t timeout)
{
thread_t thread;
uintptr_t state;
unsigned int success = 0;
thread = current_thread();
disable_preemption_for_thread(thread);
state = LCK_MTX_THREAD_TO_STATE(thread) | PLATFORM_LCK_ILOCK;
#if __SMP__
#if LOCK_PRETEST
if (ordered_load_hw(lock))
goto contended;
#endif // LOCK_PRETEST
if (atomic_compare_exchange(&lock->lock_data, 0, state,
memory_order_acquire_smp, TRUE)) {
success = 1;
goto end;
}
#if LOCK_PRETEST
contended:
#endif // LOCK_PRETEST
success = hw_lock_lock_contended(lock, state, timeout, FALSE);
end:
#else // __SMP__
(void)timeout;
if (ordered_load_hw(lock) == 0) {
ordered_store_hw(lock, state);
success = 1;
}
#endif // __SMP__
#if CONFIG_DTRACE
if (success)
LOCKSTAT_RECORD(LS_LCK_SPIN_LOCK_ACQUIRE, lock, 0);
#endif
return success;
}
boolean_t
lck_rw_try_lock_shared(
lck_rw_t *lck)
{
boolean_t istate;
istate = lck_interlock_lock(lck);
/* No reader priority check here... */
if (lck->lck_rw_want_write || lck->lck_rw_want_upgrade) {
lck_interlock_unlock(lck, istate);
return(FALSE);
}
lck->lck_rw_shared_count++;
lck_interlock_unlock(lck, istate);
#if CONFIG_DTRACE
LOCKSTAT_RECORD(LS_LCK_RW_TRY_LOCK_SHARED_ACQUIRE, lck, 0);
#endif
return(TRUE);
}
/*
* Routine: lck_mtx_lock_wait
*
* Invoked in order to wait on contention.
*
* Called with the interlock locked and
* returns it unlocked.
*/
void
lck_mtx_lock_wait (
lck_mtx_t *lck,
thread_t holder)
{
thread_t self = current_thread();
lck_mtx_t *mutex;
__kdebug_only uintptr_t trace_lck = VM_KERNEL_UNSLIDE_OR_PERM(lck);
__kdebug_only uintptr_t trace_holder = VM_KERNEL_UNSLIDE_OR_PERM(holder);
integer_t priority;
spl_t s = splsched();
#if CONFIG_DTRACE
uint64_t sleep_start = 0;
if (lockstat_probemap[LS_LCK_MTX_LOCK_BLOCK] || lockstat_probemap[LS_LCK_MTX_EXT_LOCK_BLOCK]) {
sleep_start = mach_absolute_time();
}
#endif
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT)
mutex = lck;
else
mutex = &lck->lck_mtx_ptr->lck_mtx;
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAIT_CODE) | DBG_FUNC_START, trace_lck, trace_holder, 0, 0, 0);
priority = self->sched_pri;
if (priority < self->base_pri)
priority = self->base_pri;
if (priority < BASEPRI_DEFAULT)
priority = BASEPRI_DEFAULT;
/* Do not promote past promotion ceiling */
priority = MIN(priority, MAXPRI_PROMOTE);
thread_lock(holder);
if (mutex->lck_mtx_pri == 0)
holder->promotions++;
holder->sched_flags |= TH_SFLAG_PROMOTED;
if (mutex->lck_mtx_pri < priority && holder->sched_pri < priority) {
KERNEL_DEBUG_CONSTANT(
MACHDBG_CODE(DBG_MACH_SCHED,MACH_PROMOTE) | DBG_FUNC_NONE,
holder->sched_pri, priority, trace_holder, trace_lck, 0);
set_sched_pri(holder, priority);
}
thread_unlock(holder);
splx(s);
if (mutex->lck_mtx_pri < priority)
mutex->lck_mtx_pri = priority;
if (self->pending_promoter[self->pending_promoter_index] == NULL) {
self->pending_promoter[self->pending_promoter_index] = mutex;
mutex->lck_mtx_waiters++;
}
else
if (self->pending_promoter[self->pending_promoter_index] != mutex) {
self->pending_promoter[++self->pending_promoter_index] = mutex;
mutex->lck_mtx_waiters++;
}
assert_wait(LCK_MTX_EVENT(mutex), THREAD_UNINT);
lck_mtx_ilk_unlock(mutex);
thread_block(THREAD_CONTINUE_NULL);
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAIT_CODE) | DBG_FUNC_END, 0, 0, 0, 0, 0);
#if CONFIG_DTRACE
/*
* Record the Dtrace lockstat probe for blocking, block time
* measured from when we were entered.
*/
if (sleep_start) {
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT) {
LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_BLOCK, lck,
mach_absolute_time() - sleep_start);
} else {
LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_BLOCK, lck,
mach_absolute_time() - sleep_start);
}
}
#endif
}
/*
* Routine: lck_rw_lock_shared_gen
*/
void
lck_rw_lock_shared_gen(
lck_rw_t *lck)
{
int i;
wait_result_t res;
#if MACH_LDEBUG
int decrementer;
#endif /* MACH_LDEBUG */
boolean_t istate;
#if CONFIG_DTRACE
uint64_t wait_interval = 0;
int slept = 0;
int readers_at_sleep;
#endif
istate = lck_interlock_lock(lck);
#if CONFIG_DTRACE
readers_at_sleep = lck->lck_rw_shared_count;
#endif
#if MACH_LDEBUG
decrementer = DECREMENTER_TIMEOUT;
#endif /* MACH_LDEBUG */
while ((lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl)) {
i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_CODE) | DBG_FUNC_START,
(int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, i, 0);
#if CONFIG_DTRACE
if ((lockstat_probemap[LS_LCK_RW_LOCK_SHARED_SPIN] || lockstat_probemap[LS_LCK_RW_LOCK_SHARED_BLOCK]) && wait_interval == 0) {
wait_interval = mach_absolute_time();
} else {
wait_interval = -1;
}
#endif
if (i != 0) {
lck_interlock_unlock(lck, istate);
#if MACH_LDEBUG
if (!--decrementer)
Debugger("timeout - wait no writers");
#endif /* MACH_LDEBUG */
while (--i != 0 &&
(lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl))
lck_rw_lock_pause(istate);
istate = lck_interlock_lock(lck);
}
if (lck->lck_rw_can_sleep &&
(lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl)) {
lck->lck_r_waiting = TRUE;
res = assert_wait(RW_LOCK_READER_EVENT(lck), THREAD_UNINT);
if (res == THREAD_WAITING) {
lck_interlock_unlock(lck, istate);
res = thread_block(THREAD_CONTINUE_NULL);
#if CONFIG_DTRACE
slept = 1;
#endif
istate = lck_interlock_lock(lck);
}
}
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_CODE) | DBG_FUNC_END,
(int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, res, 0);
}
lck->lck_rw_shared_count++;
lck_interlock_unlock(lck, istate);
#if CONFIG_DTRACE
if (wait_interval != 0 && wait_interval != (unsigned) -1) {
if (slept == 0) {
LOCKSTAT_RECORD2(LS_LCK_RW_LOCK_SHARED_SPIN, lck, mach_absolute_time() - wait_interval, 0);
} else {
LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_SHARED_BLOCK, lck,
mach_absolute_time() - wait_interval, 0,
(readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
}
}
LOCKSTAT_RECORD(LS_LCK_RW_LOCK_SHARED_ACQUIRE, lck, 0);
#endif
}
/*
* Routine: lck_mtx_lock_wait
*
* Invoked in order to wait on contention.
*
* Called with the interlock locked and
* returns it unlocked.
*/
void
lck_mtx_lock_wait (
lck_mtx_t *lck,
thread_t holder)
{
thread_t self = current_thread();
lck_mtx_t *mutex;
integer_t priority;
spl_t s = splsched();
#if CONFIG_DTRACE
uint64_t sleep_start = 0;
if (lockstat_probemap[LS_LCK_MTX_LOCK_BLOCK] || lockstat_probemap[LS_LCK_MTX_EXT_LOCK_BLOCK]) {
sleep_start = mach_absolute_time();
}
#endif
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT)
mutex = lck;
else
mutex = &lck->lck_mtx_ptr->lck_mtx;
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAIT_CODE) | DBG_FUNC_START, (int)lck, (int)holder, 0, 0, 0);
priority = self->sched_pri;
if (priority < self->priority)
priority = self->priority;
if (priority < BASEPRI_DEFAULT)
priority = BASEPRI_DEFAULT;
thread_lock(holder);
if (mutex->lck_mtx_pri == 0)
holder->promotions++;
holder->sched_mode |= TH_MODE_PROMOTED;
if ( mutex->lck_mtx_pri < priority &&
holder->sched_pri < priority ) {
KERNEL_DEBUG_CONSTANT(
MACHDBG_CODE(DBG_MACH_SCHED,MACH_PROMOTE) | DBG_FUNC_NONE,
holder->sched_pri, priority, (int)holder, (int)lck, 0);
set_sched_pri(holder, priority);
}
thread_unlock(holder);
splx(s);
if (mutex->lck_mtx_pri < priority)
mutex->lck_mtx_pri = priority;
if (self->pending_promoter[self->pending_promoter_index] == NULL) {
self->pending_promoter[self->pending_promoter_index] = mutex;
mutex->lck_mtx_waiters++;
}
else
if (self->pending_promoter[self->pending_promoter_index] != mutex) {
self->pending_promoter[++self->pending_promoter_index] = mutex;
mutex->lck_mtx_waiters++;
}
assert_wait((event_t)(((unsigned int*)lck)+((sizeof(lck_mtx_t)-1)/sizeof(unsigned int))), THREAD_UNINT);
lck_mtx_ilk_unlock(mutex);
thread_block(THREAD_CONTINUE_NULL);
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAIT_CODE) | DBG_FUNC_END, 0, 0, 0, 0, 0);
#if CONFIG_DTRACE
/*
* Record the Dtrace lockstat probe for blocking, block time
* measured from when we were entered.
*/
if (sleep_start) {
if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT) {
LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_BLOCK, lck,
mach_absolute_time() - sleep_start);
} else {
LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_BLOCK, lck,
mach_absolute_time() - sleep_start);
}
}
#endif
}
boolean_t
lck_rw_lock_shared_to_exclusive(
lck_rw_t *lck)
{
int i;
boolean_t do_wakeup = FALSE;
wait_result_t res;
#if MACH_LDEBUG
int decrementer;
#endif /* MACH_LDEBUG */
boolean_t istate;
#if CONFIG_DTRACE
uint64_t wait_interval = 0;
int slept = 0;
int readers_at_sleep = 0;
#endif
istate = lck_interlock_lock(lck);
lck->lck_rw_shared_count--;
if (lck->lck_rw_want_upgrade) {
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_CODE) | DBG_FUNC_START,
(int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, 0, 0);
/*
* Someone else has requested upgrade.
* Since we've released a read lock, wake
* him up.
*/
if (lck->lck_w_waiting && (lck->lck_rw_shared_count == 0)) {
lck->lck_w_waiting = FALSE;
do_wakeup = TRUE;
}
lck_interlock_unlock(lck, istate);
if (do_wakeup)
thread_wakeup(RW_LOCK_WRITER_EVENT(lck));
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_CODE) | DBG_FUNC_END,
(int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, 0, 0);
return (FALSE);
}
lck->lck_rw_want_upgrade = TRUE;
#if MACH_LDEBUG
decrementer = DECREMENTER_TIMEOUT;
#endif /* MACH_LDEBUG */
while (lck->lck_rw_shared_count != 0) {
#if CONFIG_DTRACE
if (lockstat_probemap[LS_LCK_RW_LOCK_SHARED_TO_EXCL_SPIN] && wait_interval == 0) {
wait_interval = mach_absolute_time();
readers_at_sleep = lck->lck_rw_shared_count;
} else {
wait_interval = -1;
}
#endif
i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX1_CODE) | DBG_FUNC_START,
(int)lck, lck->lck_rw_shared_count, i, 0, 0);
if (i != 0) {
lck_interlock_unlock(lck, istate);
#if MACH_LDEBUG
if (!--decrementer)
Debugger("timeout - lck_rw_shared_count");
#endif /* MACH_LDEBUG */
while (--i != 0 && lck->lck_rw_shared_count != 0)
lck_rw_lock_pause(istate);
istate = lck_interlock_lock(lck);
}
if (lck->lck_rw_can_sleep && lck->lck_rw_shared_count != 0) {
lck->lck_w_waiting = TRUE;
res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
if (res == THREAD_WAITING) {
lck_interlock_unlock(lck, istate);
res = thread_block(THREAD_CONTINUE_NULL);
#if CONFIG_DTRACE
slept = 1;
#endif
istate = lck_interlock_lock(lck);
}
}
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX1_CODE) | DBG_FUNC_END,
(int)lck, lck->lck_rw_shared_count, 0, 0, 0);
}
lck_interlock_unlock(lck, istate);
#if CONFIG_DTRACE
/*
* We infer whether we took the sleep/spin path above by checking readers_at_sleep.
*/
if (wait_interval != 0 && wait_interval != (unsigned) -1 && readers_at_sleep) {
if (slept == 0) {
LOCKSTAT_RECORD2(LS_LCK_RW_LOCK_SHARED_TO_EXCL_SPIN, lck, mach_absolute_time() - wait_interval, 0);
} else {
LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_SHARED_TO_EXCL_BLOCK, lck,
mach_absolute_time() - wait_interval, 1,
(readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
}
}
LOCKSTAT_RECORD(LS_LCK_RW_LOCK_SHARED_TO_EXCL_UPGRADE, lck, 1);
#endif
return (TRUE);
}
/*
* Routine: lck_rw_lock_exclusive
*/
void
lck_rw_lock_exclusive(
lck_rw_t *lck)
{
int i;
wait_result_t res;
#if MACH_LDEBUG
int decrementer;
#endif /* MACH_LDEBUG */
boolean_t istate;
#if CONFIG_DTRACE
uint64_t wait_interval = 0;
int slept = 0;
int readers_at_sleep;
#endif
istate = lck_interlock_lock(lck);
#if CONFIG_DTRACE
readers_at_sleep = lck->lck_rw_shared_count;
#endif
#if MACH_LDEBUG
decrementer = DECREMENTER_TIMEOUT;
#endif /* MACH_LDEBUG */
/*
* Try to acquire the lck_rw_want_write bit.
*/
while (lck->lck_rw_want_write) {
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE_CODE) | DBG_FUNC_START, (int)lck, 0, 0, 0, 0);
/*
* Either sleeping or spinning is happening, start
* a timing of our delay interval now.
*/
#if CONFIG_DTRACE
if ((lockstat_probemap[LS_LCK_RW_LOCK_EXCL_SPIN] || lockstat_probemap[LS_LCK_RW_LOCK_EXCL_BLOCK]) && wait_interval == 0) {
wait_interval = mach_absolute_time();
} else {
wait_interval = -1;
}
#endif
i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];
if (i != 0) {
lck_interlock_unlock(lck, istate);
#if MACH_LDEBUG
if (!--decrementer)
Debugger("timeout - lck_rw_want_write");
#endif /* MACH_LDEBUG */
while (--i != 0 && lck->lck_rw_want_write)
lck_rw_lock_pause(istate);
istate = lck_interlock_lock(lck);
}
if (lck->lck_rw_can_sleep && lck->lck_rw_want_write) {
lck->lck_w_waiting = TRUE;
res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
if (res == THREAD_WAITING) {
lck_interlock_unlock(lck, istate);
res = thread_block(THREAD_CONTINUE_NULL);
#if CONFIG_DTRACE
slept = 1;
#endif
istate = lck_interlock_lock(lck);
}
}
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE_CODE) | DBG_FUNC_END, (int)lck, res, 0, 0, 0);
}
lck->lck_rw_want_write = TRUE;
/* Wait for readers (and upgrades) to finish */
#if MACH_LDEBUG
decrementer = DECREMENTER_TIMEOUT;
#endif /* MACH_LDEBUG */
while ((lck->lck_rw_shared_count != 0) || lck->lck_rw_want_upgrade) {
i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE1_CODE) | DBG_FUNC_START,
(int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, i, 0);
#if CONFIG_DTRACE
/*
* Either sleeping or spinning is happening, start
* a timing of our delay interval now. If we set it
* to -1 we don't have accurate data so we cannot later
* decide to record a dtrace spin or sleep event.
*/
if ((lockstat_probemap[LS_LCK_RW_LOCK_EXCL_SPIN] || lockstat_probemap[LS_LCK_RW_LOCK_EXCL_BLOCK]) && wait_interval == 0) {
wait_interval = mach_absolute_time();
} else {
wait_interval = (unsigned) -1;
}
#endif
if (i != 0) {
lck_interlock_unlock(lck, istate);
#if MACH_LDEBUG
if (!--decrementer)
Debugger("timeout - wait for readers");
#endif /* MACH_LDEBUG */
while (--i != 0 && (lck->lck_rw_shared_count != 0 ||
lck->lck_rw_want_upgrade))
lck_rw_lock_pause(istate);
istate = lck_interlock_lock(lck);
}
if (lck->lck_rw_can_sleep && (lck->lck_rw_shared_count != 0 || lck->lck_rw_want_upgrade)) {
lck->lck_w_waiting = TRUE;
res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
if (res == THREAD_WAITING) {
lck_interlock_unlock(lck, istate);
res = thread_block(THREAD_CONTINUE_NULL);
#if CONFIG_DTRACE
slept = 1;
#endif
istate = lck_interlock_lock(lck);
}
}
KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE1_CODE) | DBG_FUNC_END,
(int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, res, 0);
}
lck_interlock_unlock(lck, istate);
#if CONFIG_DTRACE
/*
* Decide what latencies we suffered that are Dtrace events.
* If we have set wait_interval, then we either spun or slept.
* At least we get out from under the interlock before we record
* which is the best we can do here to minimize the impact
* of the tracing.
* If we have set wait_interval to -1, then dtrace was not enabled when we
* started sleeping/spinning so we don't record this event.
*/
if (wait_interval != 0 && wait_interval != (unsigned) -1) {
if (slept == 0) {
LOCKSTAT_RECORD2(LS_LCK_RW_LOCK_EXCL_SPIN, lck,
mach_absolute_time() - wait_interval, 1);
} else {
/*
* For the blocking case, we also record if when we blocked
* it was held for read or write, and how many readers.
* Notice that above we recorded this before we dropped
* the interlock so the count is accurate.
*/
LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_EXCL_BLOCK, lck,
mach_absolute_time() - wait_interval, 1,
(readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
}
}
LOCKSTAT_RECORD(LS_LCK_RW_LOCK_EXCL_ACQUIRE, lck, 1);
#endif
}
/*
* mutex_vector_enter() is called from the assembly mutex_enter() routine
* if the lock is held or is not of type MUTEX_ADAPTIVE.
*/
void
mutex_vector_enter(mutex_impl_t *lp)
{
kthread_id_t owner;
hrtime_t sleep_time = 0; /* how long we slept */
uint_t spin_count = 0; /* how many times we spun */
cpu_t *cpup, *last_cpu;
extern cpu_t *cpu_list;
turnstile_t *ts;
volatile mutex_impl_t *vlp = (volatile mutex_impl_t *)lp;
int backoff; /* current backoff */
int backctr; /* ctr for backoff */
int sleep_count = 0;
ASSERT_STACK_ALIGNED();
if (MUTEX_TYPE_SPIN(lp)) {
lock_set_spl(&lp->m_spin.m_spinlock, lp->m_spin.m_minspl,
&lp->m_spin.m_oldspl);
return;
}
if (!MUTEX_TYPE_ADAPTIVE(lp)) {
mutex_panic("mutex_enter: bad mutex", lp);
return;
}
/*
* Adaptive mutexes must not be acquired from above LOCK_LEVEL.
* We can migrate after loading CPU but before checking CPU_ON_INTR,
* so we must verify by disabling preemption and loading CPU again.
*/
cpup = CPU;
if (CPU_ON_INTR(cpup) && !panicstr) {
kpreempt_disable();
if (CPU_ON_INTR(CPU))
mutex_panic("mutex_enter: adaptive at high PIL", lp);
kpreempt_enable();
}
CPU_STATS_ADDQ(cpup, sys, mutex_adenters, 1);
if (&plat_lock_delay) {
backoff = 0;
} else {
backoff = BACKOFF_BASE;
}
for (;;) {
spin:
spin_count++;
/*
* Add an exponential backoff delay before trying again
* to touch the mutex data structure.
* the spin_count test and call to nulldev are to prevent
* the compiler optimizer from eliminating the delay loop.
*/
if (&plat_lock_delay) {
plat_lock_delay(&backoff);
} else {
for (backctr = backoff; backctr; backctr--) {
if (!spin_count) (void) nulldev();
}; /* delay */
backoff = backoff << 1; /* double it */
if (backoff > BACKOFF_CAP) {
backoff = BACKOFF_CAP;
}
SMT_PAUSE();
}
if (panicstr)
return;
if ((owner = MUTEX_OWNER(vlp)) == NULL) {
if (mutex_adaptive_tryenter(lp))
break;
continue;
}
if (owner == curthread)
mutex_panic("recursive mutex_enter", lp);
/*
* If lock is held but owner is not yet set, spin.
* (Only relevant for platforms that don't have cas.)
*/
if (owner == MUTEX_NO_OWNER)
continue;
/*
* When searching the other CPUs, start with the one where
* we last saw the owner thread. If owner is running, spin.
*
* We must disable preemption at this point to guarantee
* that the list doesn't change while we traverse it
* without the cpu_lock mutex. While preemption is
* disabled, we must revalidate our cached cpu pointer.
*/
kpreempt_disable();
if (cpup->cpu_next == NULL)
cpup = cpu_list;
last_cpu = cpup; /* mark end of search */
do {
if (cpup->cpu_thread == owner) {
kpreempt_enable();
goto spin;
}
} while ((cpup = cpup->cpu_next) != last_cpu);
kpreempt_enable();
/*
* The owner appears not to be running, so block.
* See the Big Theory Statement for memory ordering issues.
*/
ts = turnstile_lookup(lp);
MUTEX_SET_WAITERS(lp);
membar_enter();
/*
* Recheck whether owner is running after waiters bit hits
* global visibility (above). If owner is running, spin.
*
* Since we are at ipl DISP_LEVEL, kernel preemption is
* disabled, however we still need to revalidate our cached
* cpu pointer to make sure the cpu hasn't been deleted.
*/
if (cpup->cpu_next == NULL)
last_cpu = cpup = cpu_list;
do {
if (cpup->cpu_thread == owner) {
turnstile_exit(lp);
goto spin;
}
} while ((cpup = cpup->cpu_next) != last_cpu);
membar_consumer();
/*
* If owner and waiters bit are unchanged, block.
*/
if (MUTEX_OWNER(vlp) == owner && MUTEX_HAS_WAITERS(vlp)) {
sleep_time -= gethrtime();
(void) turnstile_block(ts, TS_WRITER_Q, lp,
&mutex_sobj_ops, NULL, NULL);
sleep_time += gethrtime();
sleep_count++;
} else {
turnstile_exit(lp);
}
}
ASSERT(MUTEX_OWNER(lp) == curthread);
if (sleep_time != 0) {
/*
* Note, sleep time is the sum of all the sleeping we
* did.
*/
LOCKSTAT_RECORD(LS_MUTEX_ENTER_BLOCK, lp, sleep_time);
}
/*
* We do not count a sleep as a spin.
*/
if (spin_count > sleep_count)
LOCKSTAT_RECORD(LS_MUTEX_ENTER_SPIN, lp,
spin_count - sleep_count);
LOCKSTAT_RECORD0(LS_MUTEX_ENTER_ACQUIRE, lp);
}