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locking/rwsem: Convert sem->count to 'atomic_long_t'

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Convert the rwsem count variable to an atomic_long_t since we use it
as an atomic variable. This also allows us to remove the
rwsem_atomic_{add,update}() "abstraction" which would now be an unnecesary
level of indirection. In follow up patches, we also remove the
rwsem_atomic_{add,update}() definitions across the various architectures.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jason Low <jason.low2@hpe.com>
[ Build warning fixes on various architectures. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Terry Rudd <terry.rudd@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Waiman Long <Waiman.Long@hpe.com>
Link: http://lkml.kernel.org/r/1465017963-4839-2-git-send-email-jason.low2@hpe.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Jason Low 2016-06-03 22:26:02 -07:00 • committed by Ingo Molnar
parent 055ce0fd1b
commit 8ee62b1870
5 changed files with 50 additions and 46 deletions
Download patch file Download diff file Expand all files Collapse all files

32
kernel/locking/rwsem-xadd.c
View file

@ -80,7 +80,7 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
lockdep_init_map(&sem->dep_map, name, key, 0);
#endif
sem->count = RWSEM_UNLOCKED_VALUE;
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
@ -153,10 +153,11 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
if (wake_type != RWSEM_WAKE_READ_OWNED) {
adjustment = RWSEM_ACTIVE_READ_BIAS;
try_reader_grant:
oldcount = rwsem_atomic_update(adjustment, sem) - adjustment;
oldcount = atomic_long_add_return(adjustment, &sem->count) - adjustment;
if (unlikely(oldcount < RWSEM_WAITING_BIAS)) {
/* A writer stole the lock. Undo our reader grant. */
if (rwsem_atomic_update(-adjustment, sem) &
if (atomic_long_sub_return(adjustment, &sem->count) &
RWSEM_ACTIVE_MASK)
goto out;
/* Last active locker left. Retry waking readers. */
@ -186,7 +187,7 @@ __rwsem_mark_wake(struct rw_semaphore *sem,
adjustment -= RWSEM_WAITING_BIAS;
if (adjustment)
rwsem_atomic_add(adjustment, sem);
atomic_long_add(adjustment, &sem->count);
next = sem->wait_list.next;
loop = woken;
@ -233,7 +234,7 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
list_add_tail(&waiter.list, &sem->wait_list);
/* we're now waiting on the lock, but no longer actively locking */
count = rwsem_atomic_update(adjustment, sem);
count = atomic_long_add_return(adjustment, &sem->count);
/* If there are no active locks, wake the front queued process(es).
*
@ -282,7 +283,8 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
RWSEM_ACTIVE_WRITE_BIAS :
RWSEM_ACTIVE_WRITE_BIAS + RWSEM_WAITING_BIAS;
if (cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, count) == RWSEM_WAITING_BIAS) {
if (atomic_long_cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, count)
== RWSEM_WAITING_BIAS) {
rwsem_set_owner(sem);
return true;
}
@ -296,13 +298,13 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
*/
static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
{
long old, count = READ_ONCE(sem->count);
long old, count = atomic_long_read(&sem->count);
while (true) {
if (!(count == 0 || count == RWSEM_WAITING_BIAS))
return false;
old = cmpxchg_acquire(&sem->count, count,
old = atomic_long_cmpxchg_acquire(&sem->count, count,
count + RWSEM_ACTIVE_WRITE_BIAS);
if (old == count) {
rwsem_set_owner(sem);
@ -324,7 +326,7 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
rcu_read_lock();
owner = READ_ONCE(sem->owner);
if (!owner) {
long count = READ_ONCE(sem->count);
long count = atomic_long_read(&sem->count);
/*
* If sem->owner is not set, yet we have just recently entered the
* slowpath with the lock being active, then there is a possibility
@ -375,7 +377,7 @@ bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
* held by readers. Check the counter to verify the
* state.
*/
count = READ_ONCE(sem->count);
count = atomic_long_read(&sem->count);
return (count == 0 || count == RWSEM_WAITING_BIAS);
}
@ -460,7 +462,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
WAKE_Q(wake_q);
/* undo write bias from down_write operation, stop active locking */
count = rwsem_atomic_update(-RWSEM_ACTIVE_WRITE_BIAS, sem);
count = atomic_long_sub_return(RWSEM_ACTIVE_WRITE_BIAS, &sem->count);
/* do optimistic spinning and steal lock if possible */
if (rwsem_optimistic_spin(sem))
@ -483,7 +485,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
/* we're now waiting on the lock, but no longer actively locking */
if (waiting) {
count = READ_ONCE(sem->count);
count = atomic_long_read(&sem->count);
/*
* If there were already threads queued before us and there are
@ -505,7 +507,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
}
} else
count = rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
count = atomic_long_add_return(RWSEM_WAITING_BIAS, &sem->count);
/* wait until we successfully acquire the lock */
set_current_state(state);
@ -521,7 +523,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
schedule();
set_current_state(state);
} while ((count = sem->count) & RWSEM_ACTIVE_MASK);
} while ((count = atomic_long_read(&sem->count)) & RWSEM_ACTIVE_MASK);
raw_spin_lock_irq(&sem->wait_lock);
}
@ -536,7 +538,7 @@ out_nolock:
raw_spin_lock_irq(&sem->wait_lock);
list_del(&waiter.list);
if (list_empty(&sem->wait_list))
rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem);
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);