forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
640 lines
18 KiB
640 lines
18 KiB
/* rwsem.c: R/W semaphores: contention handling functions |
|
* |
|
* Written by David Howells ([email protected]). |
|
* Derived from arch/i386/kernel/semaphore.c |
|
* |
|
* Writer lock-stealing by Alex Shi <[email protected]> |
|
* and Michel Lespinasse <[email protected]> |
|
* |
|
* Optimistic spinning by Tim Chen <[email protected]> |
|
* and Davidlohr Bueso <[email protected]>. Based on mutexes. |
|
*/ |
|
#include <linux/rwsem.h> |
|
#include <linux/sched.h> |
|
#include <linux/init.h> |
|
#include <linux/export.h> |
|
#include <linux/sched/rt.h> |
|
#include <linux/osq_lock.h> |
|
|
|
#include "rwsem.h" |
|
|
|
/* |
|
* Guide to the rw_semaphore's count field for common values. |
|
* (32-bit case illustrated, similar for 64-bit) |
|
* |
|
* 0x0000000X (1) X readers active or attempting lock, no writer waiting |
|
* X = #active_readers + #readers attempting to lock |
|
* (X*ACTIVE_BIAS) |
|
* |
|
* 0x00000000 rwsem is unlocked, and no one is waiting for the lock or |
|
* attempting to read lock or write lock. |
|
* |
|
* 0xffff000X (1) X readers active or attempting lock, with waiters for lock |
|
* X = #active readers + # readers attempting lock |
|
* (X*ACTIVE_BIAS + WAITING_BIAS) |
|
* (2) 1 writer attempting lock, no waiters for lock |
|
* X-1 = #active readers + #readers attempting lock |
|
* ((X-1)*ACTIVE_BIAS + ACTIVE_WRITE_BIAS) |
|
* (3) 1 writer active, no waiters for lock |
|
* X-1 = #active readers + #readers attempting lock |
|
* ((X-1)*ACTIVE_BIAS + ACTIVE_WRITE_BIAS) |
|
* |
|
* 0xffff0001 (1) 1 reader active or attempting lock, waiters for lock |
|
* (WAITING_BIAS + ACTIVE_BIAS) |
|
* (2) 1 writer active or attempting lock, no waiters for lock |
|
* (ACTIVE_WRITE_BIAS) |
|
* |
|
* 0xffff0000 (1) There are writers or readers queued but none active |
|
* or in the process of attempting lock. |
|
* (WAITING_BIAS) |
|
* Note: writer can attempt to steal lock for this count by adding |
|
* ACTIVE_WRITE_BIAS in cmpxchg and checking the old count |
|
* |
|
* 0xfffe0001 (1) 1 writer active, or attempting lock. Waiters on queue. |
|
* (ACTIVE_WRITE_BIAS + WAITING_BIAS) |
|
* |
|
* Note: Readers attempt to lock by adding ACTIVE_BIAS in down_read and checking |
|
* the count becomes more than 0 for successful lock acquisition, |
|
* i.e. the case where there are only readers or nobody has lock. |
|
* (1st and 2nd case above). |
|
* |
|
* Writers attempt to lock by adding ACTIVE_WRITE_BIAS in down_write and |
|
* checking the count becomes ACTIVE_WRITE_BIAS for successful lock |
|
* acquisition (i.e. nobody else has lock or attempts lock). If |
|
* unsuccessful, in rwsem_down_write_failed, we'll check to see if there |
|
* are only waiters but none active (5th case above), and attempt to |
|
* steal the lock. |
|
* |
|
*/ |
|
|
|
/* |
|
* Initialize an rwsem: |
|
*/ |
|
void __init_rwsem(struct rw_semaphore *sem, const char *name, |
|
struct lock_class_key *key) |
|
{ |
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC |
|
/* |
|
* Make sure we are not reinitializing a held semaphore: |
|
*/ |
|
debug_check_no_locks_freed((void *)sem, sizeof(*sem)); |
|
lockdep_init_map(&sem->dep_map, name, key, 0); |
|
#endif |
|
atomic_long_set(&sem->count, RWSEM_UNLOCKED_VALUE); |
|
raw_spin_lock_init(&sem->wait_lock); |
|
INIT_LIST_HEAD(&sem->wait_list); |
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
|
sem->owner = NULL; |
|
osq_lock_init(&sem->osq); |
|
#endif |
|
} |
|
|
|
EXPORT_SYMBOL(__init_rwsem); |
|
|
|
enum rwsem_waiter_type { |
|
RWSEM_WAITING_FOR_WRITE, |
|
RWSEM_WAITING_FOR_READ |
|
}; |
|
|
|
struct rwsem_waiter { |
|
struct list_head list; |
|
struct task_struct *task; |
|
enum rwsem_waiter_type type; |
|
}; |
|
|
|
enum rwsem_wake_type { |
|
RWSEM_WAKE_ANY, /* Wake whatever's at head of wait list */ |
|
RWSEM_WAKE_READERS, /* Wake readers only */ |
|
RWSEM_WAKE_READ_OWNED /* Waker thread holds the read lock */ |
|
}; |
|
|
|
/* |
|
* handle the lock release when processes blocked on it that can now run |
|
* - if we come here from up_xxxx(), then: |
|
* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed) |
|
* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so) |
|
* - there must be someone on the queue |
|
* - the wait_lock must be held by the caller |
|
* - tasks are marked for wakeup, the caller must later invoke wake_up_q() |
|
* to actually wakeup the blocked task(s) and drop the reference count, |
|
* preferably when the wait_lock is released |
|
* - woken process blocks are discarded from the list after having task zeroed |
|
* - writers are only marked woken if downgrading is false |
|
*/ |
|
static void __rwsem_mark_wake(struct rw_semaphore *sem, |
|
enum rwsem_wake_type wake_type, |
|
struct wake_q_head *wake_q) |
|
{ |
|
struct rwsem_waiter *waiter, *tmp; |
|
long oldcount, woken = 0, adjustment = 0; |
|
|
|
/* |
|
* Take a peek at the queue head waiter such that we can determine |
|
* the wakeup(s) to perform. |
|
*/ |
|
waiter = list_first_entry(&sem->wait_list, struct rwsem_waiter, list); |
|
|
|
if (waiter->type == RWSEM_WAITING_FOR_WRITE) { |
|
if (wake_type == RWSEM_WAKE_ANY) { |
|
/* |
|
* Mark writer at the front of the queue for wakeup. |
|
* Until the task is actually later awoken later by |
|
* the caller, other writers are able to steal it. |
|
* Readers, on the other hand, will block as they |
|
* will notice the queued writer. |
|
*/ |
|
wake_q_add(wake_q, waiter->task); |
|
} |
|
|
|
return; |
|
} |
|
|
|
/* |
|
* Writers might steal the lock before we grant it to the next reader. |
|
* We prefer to do the first reader grant before counting readers |
|
* so we can bail out early if a writer stole the lock. |
|
*/ |
|
if (wake_type != RWSEM_WAKE_READ_OWNED) { |
|
adjustment = RWSEM_ACTIVE_READ_BIAS; |
|
try_reader_grant: |
|
oldcount = atomic_long_fetch_add(adjustment, &sem->count); |
|
if (unlikely(oldcount < RWSEM_WAITING_BIAS)) { |
|
/* |
|
* If the count is still less than RWSEM_WAITING_BIAS |
|
* after removing the adjustment, it is assumed that |
|
* a writer has stolen the lock. We have to undo our |
|
* reader grant. |
|
*/ |
|
if (atomic_long_add_return(-adjustment, &sem->count) < |
|
RWSEM_WAITING_BIAS) |
|
return; |
|
|
|
/* Last active locker left. Retry waking readers. */ |
|
goto try_reader_grant; |
|
} |
|
/* |
|
* It is not really necessary to set it to reader-owned here, |
|
* but it gives the spinners an early indication that the |
|
* readers now have the lock. |
|
*/ |
|
rwsem_set_reader_owned(sem); |
|
} |
|
|
|
/* |
|
* Grant an infinite number of read locks to the readers at the front |
|
* of the queue. We know that woken will be at least 1 as we accounted |
|
* for above. Note we increment the 'active part' of the count by the |
|
* number of readers before waking any processes up. |
|
*/ |
|
list_for_each_entry_safe(waiter, tmp, &sem->wait_list, list) { |
|
struct task_struct *tsk; |
|
|
|
if (waiter->type == RWSEM_WAITING_FOR_WRITE) |
|
break; |
|
|
|
woken++; |
|
tsk = waiter->task; |
|
|
|
wake_q_add(wake_q, tsk); |
|
list_del(&waiter->list); |
|
/* |
|
* Ensure that the last operation is setting the reader |
|
* waiter to nil such that rwsem_down_read_failed() cannot |
|
* race with do_exit() by always holding a reference count |
|
* to the task to wakeup. |
|
*/ |
|
smp_store_release(&waiter->task, NULL); |
|
} |
|
|
|
adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment; |
|
if (list_empty(&sem->wait_list)) { |
|
/* hit end of list above */ |
|
adjustment -= RWSEM_WAITING_BIAS; |
|
} |
|
|
|
if (adjustment) |
|
atomic_long_add(adjustment, &sem->count); |
|
} |
|
|
|
/* |
|
* Wait for the read lock to be granted |
|
*/ |
|
__visible |
|
struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) |
|
{ |
|
long count, adjustment = -RWSEM_ACTIVE_READ_BIAS; |
|
struct rwsem_waiter waiter; |
|
struct task_struct *tsk = current; |
|
WAKE_Q(wake_q); |
|
|
|
waiter.task = tsk; |
|
waiter.type = RWSEM_WAITING_FOR_READ; |
|
|
|
raw_spin_lock_irq(&sem->wait_lock); |
|
if (list_empty(&sem->wait_list)) |
|
adjustment += RWSEM_WAITING_BIAS; |
|
list_add_tail(&waiter.list, &sem->wait_list); |
|
|
|
/* we're now waiting on the lock, but no longer actively locking */ |
|
count = atomic_long_add_return(adjustment, &sem->count); |
|
|
|
/* |
|
* If there are no active locks, wake the front queued process(es). |
|
* |
|
* If there are no writers and we are first in the queue, |
|
* wake our own waiter to join the existing active readers ! |
|
*/ |
|
if (count == RWSEM_WAITING_BIAS || |
|
(count > RWSEM_WAITING_BIAS && |
|
adjustment != -RWSEM_ACTIVE_READ_BIAS)) |
|
__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q); |
|
|
|
raw_spin_unlock_irq(&sem->wait_lock); |
|
wake_up_q(&wake_q); |
|
|
|
/* wait to be given the lock */ |
|
while (true) { |
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE); |
|
if (!waiter.task) |
|
break; |
|
schedule(); |
|
} |
|
|
|
__set_task_state(tsk, TASK_RUNNING); |
|
return sem; |
|
} |
|
EXPORT_SYMBOL(rwsem_down_read_failed); |
|
|
|
/* |
|
* This function must be called with the sem->wait_lock held to prevent |
|
* race conditions between checking the rwsem wait list and setting the |
|
* sem->count accordingly. |
|
*/ |
|
static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem) |
|
{ |
|
/* |
|
* Avoid trying to acquire write lock if count isn't RWSEM_WAITING_BIAS. |
|
*/ |
|
if (count != RWSEM_WAITING_BIAS) |
|
return false; |
|
|
|
/* |
|
* Acquire the lock by trying to set it to ACTIVE_WRITE_BIAS. If there |
|
* are other tasks on the wait list, we need to add on WAITING_BIAS. |
|
*/ |
|
count = list_is_singular(&sem->wait_list) ? |
|
RWSEM_ACTIVE_WRITE_BIAS : |
|
RWSEM_ACTIVE_WRITE_BIAS + RWSEM_WAITING_BIAS; |
|
|
|
if (atomic_long_cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, count) |
|
== RWSEM_WAITING_BIAS) { |
|
rwsem_set_owner(sem); |
|
return true; |
|
} |
|
|
|
return false; |
|
} |
|
|
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER |
|
/* |
|
* Try to acquire write lock before the writer has been put on wait queue. |
|
*/ |
|
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem) |
|
{ |
|
long old, count = atomic_long_read(&sem->count); |
|
|
|
while (true) { |
|
if (!(count == 0 || count == RWSEM_WAITING_BIAS)) |
|
return false; |
|
|
|
old = atomic_long_cmpxchg_acquire(&sem->count, count, |
|
count + RWSEM_ACTIVE_WRITE_BIAS); |
|
if (old == count) { |
|
rwsem_set_owner(sem); |
|
return true; |
|
} |
|
|
|
count = old; |
|
} |
|
} |
|
|
|
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem) |
|
{ |
|
struct task_struct *owner; |
|
bool ret = true; |
|
|
|
if (need_resched()) |
|
return false; |
|
|
|
rcu_read_lock(); |
|
owner = READ_ONCE(sem->owner); |
|
if (!rwsem_owner_is_writer(owner)) { |
|
/* |
|
* Don't spin if the rwsem is readers owned. |
|
*/ |
|
ret = !rwsem_owner_is_reader(owner); |
|
goto done; |
|
} |
|
|
|
ret = owner->on_cpu; |
|
done: |
|
rcu_read_unlock(); |
|
return ret; |
|
} |
|
|
|
/* |
|
* Return true only if we can still spin on the owner field of the rwsem. |
|
*/ |
|
static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem) |
|
{ |
|
struct task_struct *owner = READ_ONCE(sem->owner); |
|
|
|
if (!rwsem_owner_is_writer(owner)) |
|
goto out; |
|
|
|
rcu_read_lock(); |
|
while (sem->owner == owner) { |
|
/* |
|
* Ensure we emit the owner->on_cpu, dereference _after_ |
|
* checking sem->owner still matches owner, if that fails, |
|
* owner might point to free()d memory, if it still matches, |
|
* the rcu_read_lock() ensures the memory stays valid. |
|
*/ |
|
barrier(); |
|
|
|
/* abort spinning when need_resched or owner is not running */ |
|
if (!owner->on_cpu || need_resched()) { |
|
rcu_read_unlock(); |
|
return false; |
|
} |
|
|
|
cpu_relax_lowlatency(); |
|
} |
|
rcu_read_unlock(); |
|
out: |
|
/* |
|
* If there is a new owner or the owner is not set, we continue |
|
* spinning. |
|
*/ |
|
return !rwsem_owner_is_reader(READ_ONCE(sem->owner)); |
|
} |
|
|
|
static bool rwsem_optimistic_spin(struct rw_semaphore *sem) |
|
{ |
|
bool taken = false; |
|
|
|
preempt_disable(); |
|
|
|
/* sem->wait_lock should not be held when doing optimistic spinning */ |
|
if (!rwsem_can_spin_on_owner(sem)) |
|
goto done; |
|
|
|
if (!osq_lock(&sem->osq)) |
|
goto done; |
|
|
|
/* |
|
* Optimistically spin on the owner field and attempt to acquire the |
|
* lock whenever the owner changes. Spinning will be stopped when: |
|
* 1) the owning writer isn't running; or |
|
* 2) readers own the lock as we can't determine if they are |
|
* actively running or not. |
|
*/ |
|
while (rwsem_spin_on_owner(sem)) { |
|
/* |
|
* Try to acquire the lock |
|
*/ |
|
if (rwsem_try_write_lock_unqueued(sem)) { |
|
taken = true; |
|
break; |
|
} |
|
|
|
/* |
|
* 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 (!sem->owner && (need_resched() || rt_task(current))) |
|
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_lowlatency(); |
|
} |
|
osq_unlock(&sem->osq); |
|
done: |
|
preempt_enable(); |
|
return taken; |
|
} |
|
|
|
/* |
|
* Return true if the rwsem has active spinner |
|
*/ |
|
static inline bool rwsem_has_spinner(struct rw_semaphore *sem) |
|
{ |
|
return osq_is_locked(&sem->osq); |
|
} |
|
|
|
#else |
|
static bool rwsem_optimistic_spin(struct rw_semaphore *sem) |
|
{ |
|
return false; |
|
} |
|
|
|
static inline bool rwsem_has_spinner(struct rw_semaphore *sem) |
|
{ |
|
return false; |
|
} |
|
#endif |
|
|
|
/* |
|
* Wait until we successfully acquire the write lock |
|
*/ |
|
static inline struct rw_semaphore * |
|
__rwsem_down_write_failed_common(struct rw_semaphore *sem, int state) |
|
{ |
|
long count; |
|
bool waiting = true; /* any queued threads before us */ |
|
struct rwsem_waiter waiter; |
|
struct rw_semaphore *ret = sem; |
|
WAKE_Q(wake_q); |
|
|
|
/* undo write bias from down_write operation, stop active locking */ |
|
count = atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS, &sem->count); |
|
|
|
/* do optimistic spinning and steal lock if possible */ |
|
if (rwsem_optimistic_spin(sem)) |
|
return sem; |
|
|
|
/* |
|
* Optimistic spinning failed, proceed to the slowpath |
|
* and block until we can acquire the sem. |
|
*/ |
|
waiter.task = current; |
|
waiter.type = RWSEM_WAITING_FOR_WRITE; |
|
|
|
raw_spin_lock_irq(&sem->wait_lock); |
|
|
|
/* account for this before adding a new element to the list */ |
|
if (list_empty(&sem->wait_list)) |
|
waiting = false; |
|
|
|
list_add_tail(&waiter.list, &sem->wait_list); |
|
|
|
/* we're now waiting on the lock, but no longer actively locking */ |
|
if (waiting) { |
|
count = atomic_long_read(&sem->count); |
|
|
|
/* |
|
* If there were already threads queued before us and there are |
|
* no active writers, the lock must be read owned; so we try to |
|
* wake any read locks that were queued ahead of us. |
|
*/ |
|
if (count > RWSEM_WAITING_BIAS) { |
|
WAKE_Q(wake_q); |
|
|
|
__rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q); |
|
/* |
|
* The wakeup is normally called _after_ the wait_lock |
|
* is released, but given that we are proactively waking |
|
* readers we can deal with the wake_q overhead as it is |
|
* similar to releasing and taking the wait_lock again |
|
* for attempting rwsem_try_write_lock(). |
|
*/ |
|
wake_up_q(&wake_q); |
|
} |
|
|
|
} else |
|
count = atomic_long_add_return(RWSEM_WAITING_BIAS, &sem->count); |
|
|
|
/* wait until we successfully acquire the lock */ |
|
set_current_state(state); |
|
while (true) { |
|
if (rwsem_try_write_lock(count, sem)) |
|
break; |
|
raw_spin_unlock_irq(&sem->wait_lock); |
|
|
|
/* Block until there are no active lockers. */ |
|
do { |
|
if (signal_pending_state(state, current)) |
|
goto out_nolock; |
|
|
|
schedule(); |
|
set_current_state(state); |
|
} while ((count = atomic_long_read(&sem->count)) & RWSEM_ACTIVE_MASK); |
|
|
|
raw_spin_lock_irq(&sem->wait_lock); |
|
} |
|
__set_current_state(TASK_RUNNING); |
|
list_del(&waiter.list); |
|
raw_spin_unlock_irq(&sem->wait_lock); |
|
|
|
return ret; |
|
|
|
out_nolock: |
|
__set_current_state(TASK_RUNNING); |
|
raw_spin_lock_irq(&sem->wait_lock); |
|
list_del(&waiter.list); |
|
if (list_empty(&sem->wait_list)) |
|
atomic_long_add(-RWSEM_WAITING_BIAS, &sem->count); |
|
else |
|
__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q); |
|
raw_spin_unlock_irq(&sem->wait_lock); |
|
wake_up_q(&wake_q); |
|
|
|
return ERR_PTR(-EINTR); |
|
} |
|
|
|
__visible struct rw_semaphore * __sched |
|
rwsem_down_write_failed(struct rw_semaphore *sem) |
|
{ |
|
return __rwsem_down_write_failed_common(sem, TASK_UNINTERRUPTIBLE); |
|
} |
|
EXPORT_SYMBOL(rwsem_down_write_failed); |
|
|
|
__visible struct rw_semaphore * __sched |
|
rwsem_down_write_failed_killable(struct rw_semaphore *sem) |
|
{ |
|
return __rwsem_down_write_failed_common(sem, TASK_KILLABLE); |
|
} |
|
EXPORT_SYMBOL(rwsem_down_write_failed_killable); |
|
|
|
/* |
|
* handle waking up a waiter on the semaphore |
|
* - up_read/up_write has decremented the active part of count if we come here |
|
*/ |
|
__visible |
|
struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem) |
|
{ |
|
unsigned long flags; |
|
WAKE_Q(wake_q); |
|
|
|
/* |
|
* If a spinner is present, it is not necessary to do the wakeup. |
|
* Try to do wakeup only if the trylock succeeds to minimize |
|
* spinlock contention which may introduce too much delay in the |
|
* unlock operation. |
|
* |
|
* spinning writer up_write/up_read caller |
|
* --------------- ----------------------- |
|
* [S] osq_unlock() [L] osq |
|
* MB RMB |
|
* [RmW] rwsem_try_write_lock() [RmW] spin_trylock(wait_lock) |
|
* |
|
* Here, it is important to make sure that there won't be a missed |
|
* wakeup while the rwsem is free and the only spinning writer goes |
|
* to sleep without taking the rwsem. Even when the spinning writer |
|
* is just going to break out of the waiting loop, it will still do |
|
* a trylock in rwsem_down_write_failed() before sleeping. IOW, if |
|
* rwsem_has_spinner() is true, it will guarantee at least one |
|
* trylock attempt on the rwsem later on. |
|
*/ |
|
if (rwsem_has_spinner(sem)) { |
|
/* |
|
* The smp_rmb() here is to make sure that the spinner |
|
* state is consulted before reading the wait_lock. |
|
*/ |
|
smp_rmb(); |
|
if (!raw_spin_trylock_irqsave(&sem->wait_lock, flags)) |
|
return sem; |
|
goto locked; |
|
} |
|
raw_spin_lock_irqsave(&sem->wait_lock, flags); |
|
locked: |
|
|
|
if (!list_empty(&sem->wait_list)) |
|
__rwsem_mark_wake(sem, RWSEM_WAKE_ANY, &wake_q); |
|
|
|
raw_spin_unlock_irqrestore(&sem->wait_lock, flags); |
|
wake_up_q(&wake_q); |
|
|
|
return sem; |
|
} |
|
EXPORT_SYMBOL(rwsem_wake); |
|
|
|
/* |
|
* downgrade a write lock into a read lock |
|
* - caller incremented waiting part of count and discovered it still negative |
|
* - just wake up any readers at the front of the queue |
|
*/ |
|
__visible |
|
struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem) |
|
{ |
|
unsigned long flags; |
|
WAKE_Q(wake_q); |
|
|
|
raw_spin_lock_irqsave(&sem->wait_lock, flags); |
|
|
|
if (!list_empty(&sem->wait_list)) |
|
__rwsem_mark_wake(sem, RWSEM_WAKE_READ_OWNED, &wake_q); |
|
|
|
raw_spin_unlock_irqrestore(&sem->wait_lock, flags); |
|
wake_up_q(&wake_q); |
|
|
|
return sem; |
|
} |
|
EXPORT_SYMBOL(rwsem_downgrade_wake);
|
|
|