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Date: Mon, 16 May 2016 17:38:01 -0700
From: Jason Low <jason.low2@....com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>,
Richard Henderson <rth@...ddle.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ivan Kokshaysky <ink@...assic.park.msu.ru>,
Matt Turner <mattst88@...il.com>,
Tony Luck <tony.luck@...el.com>,
Fenghua Yu <fenghua.yu@...el.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Terry Rudd <terry.rudd@....com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
Arnd Bergmann <arnd@...db.de>,
Christoph Lameter <cl@...ux.com>,
Davidlohr Bueso <dave@...olabs.net>,
Waiman Long <Waiman.Long@....com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Peter Hurley <peter@...leysoftware.com>,
Jason Low <jason.low2@...com>, Jason Low <jason.low2@....com>
Subject: [RFC][PATCH 2/7] locking/rwsem: Convert sem->count to atomic_long_t
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@...radead.org>
Signed-off-by: Jason Low <jason.low2@....com>
---
include/linux/rwsem.h | 6 +++---
kernel/locking/rwsem-xadd.c | 31 ++++++++++++++++---------------
2 files changed, 19 insertions(+), 18 deletions(-)
diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index d1c12d1..e3d5a00 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -26,7 +26,7 @@ struct rw_semaphore;
#else
/* All arch specific implementations share the same struct */
struct rw_semaphore {
- long count;
+ atomic_long_t count;
struct list_head wait_list;
raw_spinlock_t wait_lock;
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
@@ -54,7 +54,7 @@ extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
/* In all implementations count != 0 means locked */
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
- return sem->count != 0;
+ return atomic_long_read(&sem->count) != 0;
}
#endif
@@ -74,7 +74,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
#endif
#define __RWSEM_INITIALIZER(name) \
- { .count = RWSEM_UNLOCKED_VALUE, \
+ { .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE), \
.wait_list = LIST_HEAD_INIT((name).wait_list), \
.wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
__RWSEM_OPT_INIT(name) \
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 296d421..d5ecec3 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -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
@@ -146,10 +146,11 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type)
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. */
@@ -179,7 +180,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type)
adjustment -= RWSEM_WAITING_BIAS;
if (adjustment)
- rwsem_atomic_add(adjustment, sem);
+ atomic_long_add(adjustment, &sem->count);
next = sem->wait_list.next;
loop = woken;
@@ -228,7 +229,7 @@ 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).
*
@@ -276,7 +277,8 @@ 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;
}
@@ -290,13 +292,13 @@ 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);
@@ -318,7 +320,7 @@ 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
@@ -369,7 +371,7 @@ 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);
}
@@ -453,7 +455,7 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
struct rw_semaphore *ret = sem;
/* 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))
@@ -476,7 +478,7 @@ __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
@@ -485,9 +487,8 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
*/
if (count > RWSEM_WAITING_BIAS)
sem = __rwsem_do_wake(sem, RWSEM_WAKE_READERS);
-
} 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);
@@ -503,7 +504,7 @@ __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);
}
--
2.1.4
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