Release 4.15 kernel/locking/rwsem-xadd.c
// SPDX-License-Identifier: GPL-2.0
/* rwsem.c: R/W semaphores: contention handling functions
*
* Written by David Howells (dhowells@redhat.com).
* Derived from arch/i386/kernel/semaphore.c
*
* Writer lock-stealing by Alex Shi <alex.shi@intel.com>
* and Michel Lespinasse <walken@google.com>
*
* Optimistic spinning by Tim Chen <tim.c.chen@intel.com>
* and Davidlohr Bueso <davidlohr@hp.com>. Based on mutexes.
*/
#include <linux/rwsem.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched/signal.h>
#include <linux/sched/rt.h>
#include <linux/sched/wake_q.h>
#include <linux/sched/debug.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
}
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| Thomas Gleixner | 1 | 1.00% | 1 | 12.50% |
| Total | 100 | 100.00% | 8 | 100.00% |
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);
}
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| Waiman Long | 11 | 4.40% | 2 | 10.53% |
| Jason Low | 10 | 4.00% | 1 | 5.26% |
| David Howells | 5 | 2.00% | 1 | 5.26% |
| Peter Zijlstra | 1 | 0.40% | 1 | 5.26% |
| Alex Shi | 1 | 0.40% | 1 | 5.26% |
| Total | 250 | 100.00% | 19 | 100.00% |
/*
* Wait for the read lock to be granted
*/
static inline struct rw_semaphore __sched *
__rwsem_down_read_failed_common(struct rw_semaphore *sem, int state)
{
long count, adjustment = -RWSEM_ACTIVE_READ_BIAS;
struct rwsem_waiter waiter;
DEFINE_WAKE_Q(wake_q);
waiter.task = current;
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_current_state(state);
if (!waiter.task)
break;
if (signal_pending_state(state, current)) {
raw_spin_lock_irq(&sem->wait_lock);
if (waiter.task)
goto out_nolock;
raw_spin_unlock_irq(&sem->wait_lock);
break;
}
schedule();
}
__set_current_state(TASK_RUNNING);
return sem;
out_nolock:
list_del(&waiter.list);
if (list_empty(&sem->wait_list))
atomic_long_add(-RWSEM_WAITING_BIAS, &sem->count);
raw_spin_unlock_irq(&sem->wait_lock);
__set_current_state(TASK_RUNNING);
return ERR_PTR(-EINTR);
}
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| Kirill Tkhai | 96 | 37.50% | 1 | 3.85% |
| Linus Torvalds | 68 | 26.56% | 5 | 19.23% |
| Michel Lespinasse | 62 | 24.22% | 9 | 34.62% |
| Davidlohr Bueso A | 22 | 8.59% | 6 | 23.08% |
| Jason Low | 4 | 1.56% | 1 | 3.85% |
| David Howells | 1 | 0.39% | 1 | 3.85% |
| Waiman Long | 1 | 0.39% | 1 | 3.85% |
| Livio Soares | 1 | 0.39% | 1 | 3.85% |
| Thomas Gleixner | 1 | 0.39% | 1 | 3.85% |
| Total | 256 | 100.00% | 26 | 100.00% |
__visible struct rw_semaphore * __sched
rwsem_down_read_failed(struct rw_semaphore *sem)
{
return __rwsem_down_read_failed_common(sem, TASK_UNINTERRUPTIBLE);
}
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| Kirill Tkhai | 21 | 95.45% | 1 | 50.00% |
| Linus Torvalds | 1 | 4.55% | 1 | 50.00% |
| Total | 22 | 100.00% | 2 | 100.00% |
EXPORT_SYMBOL(rwsem_down_read_failed);
__visible struct rw_semaphore * __sched
rwsem_down_read_failed_killable(struct rw_semaphore *sem)
{
return __rwsem_down_read_failed_common(sem, TASK_KILLABLE);
}
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EXPORT_SYMBOL(rwsem_down_read_failed_killable);
/*
* 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;
}
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| Michel Lespinasse | 9 | 12.68% | 1 | 12.50% |
| Total | 71 | 100.00% | 8 | 100.00% |
#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;
}
}
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| Davidlohr Bueso A | 54 | 65.06% | 3 | 37.50% |
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| Jason Low | 3 | 3.61% | 1 | 12.50% |
| Total | 83 | 100.00% | 8 | 100.00% |
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;
}
/*
* As lock holder preemption issue, we both skip spinning if task is not
* on cpu or its cpu is preempted
*/
ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
done:
rcu_read_unlock();
return ret;
}
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| Michel Lespinasse | 2 | 2.27% | 2 | 25.00% |
| Jason Low | 1 | 1.14% | 1 | 12.50% |
| Total | 88 | 100.00% | 8 | 100.00% |
/*
* 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 or
* owner's cpu is preempted.
*/
if (!owner->on_cpu || need_resched() ||
vcpu_is_preempted(task_cpu(owner))) {
rcu_read_unlock();
return false;
}
cpu_relax();
}
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));
}
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| Pan Xinhui | 9 | 9.00% | 1 | 14.29% |
| Christian Bornträger | 1 | 1.00% | 1 | 14.29% |
| Total | 100 | 100.00% | 7 | 100.00% |
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();
}
osq_unlock(&sem->osq);
done:
preempt_enable();
return taken;
}
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| Christian Bornträger | 1 | 0.92% | 1 | 33.33% |
| Total | 109 | 100.00% | 3 | 100.00% |
/*
* Return true if the rwsem has active spinner
*/
static inline bool rwsem_has_spinner(struct rw_semaphore *sem)
{
return osq_is_locked(&sem->osq);
}
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#else
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
return false;
}
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static inline bool rwsem_has_spinner(struct rw_semaphore *sem)
{
return false;
}
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#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;
DEFINE_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) {
__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);
/*
* Reinitialize wake_q after use.
*/
wake_q_init(&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);
}
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| Michel Lespinasse | 42 | 11.76% | 4 | 33.33% |
| Michal Hocko | 29 | 8.12% | 1 | 8.33% |
| Jason Low | 18 | 5.04% | 1 | 8.33% |
| Waiman Long | 8 | 2.24% | 2 | 16.67% |
| Andrew Morton | 1 | 0.28% | 1 | 8.33% |
| Total | 357 | 100.00% | 12 | 100.00% |
__visible struct rw_semaphore * __sched
rwsem_down_write_failed(struct rw_semaphore *sem)
{
return __rwsem_down_write_failed_common(sem, TASK_UNINTERRUPTIBLE);
}
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| Michal Hocko | 19 | 86.36% | 1 | 33.33% |
| Linus Torvalds | 2 | 9.09% | 1 | 33.33% |
| Michel Lespinasse | 1 | 4.55% | 1 | 33.33% |
| Total | 22 | 100.00% | 3 | 100.00% |
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);
}
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| Michal Hocko | 22 | 100.00% | 1 | 100.00% |
| Total | 22 | 100.00% | 1 | 100.00% |
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;
DEFINE_WAKE_Q(wake_q);
/*
* __rwsem_down_write_failed_common(sem)
* rwsem_optimistic_spin(sem)
* osq_unlock(sem->osq)
* ...
* atomic_long_add_return(&sem->count)
*
* - VS -
*
* __up_write()
* if (atomic_long_sub_return_release(&sem->count) < 0)
* rwsem_wake(sem)
* osq_is_locked(&sem->osq)
*
* And __up_write() must observe !osq_is_locked() when it observes the
* atomic_long_add_return() in order to not miss a wakeup.
*
* This boils down to:
*
* [S.rel] X = 1 [RmW] r0 = (Y += 0)
* MB RMB
* [RmW] Y += 1 [L] r1 = X
*
* exists (r0=1 /\ r1=0)
*/
smp_rmb();
/*
* 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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Linus Torvalds | 44 | 39.64% | 3 | 25.00% |
| Waiman Long | 36 | 32.43% | 2 | 16.67% |
| Davidlohr Bueso A | 14 | 12.61% | 1 | 8.33% |
| David Howells | 9 | 8.11% | 2 | 16.67% |
| Prateek Sood | 4 | 3.60% | 1 | 8.33% |
| Thomas Gleixner | 2 | 1.80% | 1 | 8.33% |
| Michel Lespinasse | 1 | 0.90% | 1 | 8.33% |
| Andi Kleen | 1 | 0.90% | 1 | 8.33% |
| Total | 111 | 100.00% | 12 | 100.00% |
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;
DEFINE_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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| David Howells | 53 | 73.61% | 2 | 28.57% |
| Davidlohr Bueso A | 14 | 19.44% | 1 | 14.29% |
| Thomas Gleixner | 2 | 2.78% | 1 | 14.29% |
| Michel Lespinasse | 1 | 1.39% | 1 | 14.29% |
| Andi Kleen | 1 | 1.39% | 1 | 14.29% |
| Waiman Long | 1 | 1.39% | 1 | 14.29% |
| Total | 72 | 100.00% | 7 | 100.00% |
EXPORT_SYMBOL(rwsem_downgrade_wake);
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Davidlohr Bueso A | 690 | 37.18% | 15 | 20.27% |
| Michel Lespinasse | 243 | 13.09% | 16 | 21.62% |
| Linus Torvalds | 215 | 11.58% | 6 | 8.11% |
| Kirill Tkhai | 144 | 7.76% | 1 | 1.35% |
| Waiman Long | 137 | 7.38% | 6 | 8.11% |
| Ingo Molnar | 88 | 4.74% | 4 | 5.41% |
| Jason Low | 83 | 4.47% | 6 | 8.11% |
| Michal Hocko | 75 | 4.04% | 1 | 1.35% |
| David Howells | 72 | 3.88% | 3 | 4.05% |
| Peter Zijlstra | 66 | 3.56% | 3 | 4.05% |
| Pan Xinhui | 19 | 1.02% | 1 | 1.35% |
| Thomas Gleixner | 6 | 0.32% | 1 | 1.35% |
| Prateek Sood | 4 | 0.22% | 1 | 1.35% |
| Andrew Morton | 3 | 0.16% | 2 | 2.70% |
| Andi Kleen | 2 | 0.11% | 1 | 1.35% |
| Christian Bornträger | 2 | 0.11% | 1 | 1.35% |
| Nicholas Piggin | 2 | 0.11% | 1 | 1.35% |
| Geert Uytterhoeven | 1 | 0.05% | 1 | 1.35% |
| Alex Shi | 1 | 0.05% | 1 | 1.35% |
| Greg Kroah-Hartman | 1 | 0.05% | 1 | 1.35% |
| Tim Chen | 1 | 0.05% | 1 | 1.35% |
| Livio Soares | 1 | 0.05% | 1 | 1.35% |
| Total | 1856 | 100.00% | 74 | 100.00% |
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