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Message-ID: <1424662301.6539.18.camel@stgolabs.net>
Date: Sun, 22 Feb 2015 19:31:41 -0800
From: Davidlohr Bueso <dave@...olabs.net>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Davidlohr Bueso <dbueso@...e.de>, linux-kernel@...r.kernel.org
Subject: [PATCH -tip] locking: Deprecate ACCESS_ONCE
With the new standardized functions, we can replace all
ACCESS_ONCE calls across relevant locking - this includes
lockref and seqlock while at it.
ACCESS_ONCE does not work reliably on non-scalar types.
For example gcc 4.6 and 4.7 might remove the volatile tag
for such accesses during the SRA (scalar replacement of
aggregates) step (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
Update the new calls regardless of if it is a scalar type,
this is cleaner than having three alternatives.
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
include/linux/seqlock.h | 6 +++---
kernel/locking/mcs_spinlock.h | 6 +++---
kernel/locking/mutex.c | 8 ++++----
kernel/locking/osq_lock.c | 14 +++++++-------
kernel/locking/rwsem-xadd.c | 10 +++++-----
lib/lockref.c | 2 +-
6 files changed, 23 insertions(+), 23 deletions(-)
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index f5df8f6..5f68d0a 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -108,7 +108,7 @@ static inline unsigned __read_seqcount_begin(const seqcount_t *s)
unsigned ret;
repeat:
- ret = ACCESS_ONCE(s->sequence);
+ ret = READ_ONCE(s->sequence);
if (unlikely(ret & 1)) {
cpu_relax();
goto repeat;
@@ -127,7 +127,7 @@ repeat:
*/
static inline unsigned raw_read_seqcount(const seqcount_t *s)
{
- unsigned ret = ACCESS_ONCE(s->sequence);
+ unsigned ret = READ_ONCE(s->sequence);
smp_rmb();
return ret;
}
@@ -179,7 +179,7 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s)
*/
static inline unsigned raw_seqcount_begin(const seqcount_t *s)
{
- unsigned ret = ACCESS_ONCE(s->sequence);
+ unsigned ret = READ_ONCE(s->sequence);
smp_rmb();
return ret & ~1;
}
diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index d1fe2ba..75e114b 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/kernel/locking/mcs_spinlock.h
@@ -78,7 +78,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
*/
return;
}
- ACCESS_ONCE(prev->next) = node;
+ WRITE_ONCE(prev->next, node);
/* Wait until the lock holder passes the lock down. */
arch_mcs_spin_lock_contended(&node->locked);
@@ -91,7 +91,7 @@ void mcs_spin_lock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
static inline
void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
{
- struct mcs_spinlock *next = ACCESS_ONCE(node->next);
+ struct mcs_spinlock *next = READ_ONCE(node->next);
if (likely(!next)) {
/*
@@ -100,7 +100,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
if (likely(cmpxchg(lock, node, NULL) == node))
return;
/* Wait until the next pointer is set */
- while (!(next = ACCESS_ONCE(node->next)))
+ while (!(next = READ_ONCE(node->next)))
cpu_relax_lowlatency();
}
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 43bf25e..16b2d3c 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -266,7 +266,7 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
return 0;
rcu_read_lock();
- owner = ACCESS_ONCE(lock->owner);
+ owner = READ_ONCE(lock->owner);
if (owner)
retval = owner->on_cpu;
rcu_read_unlock();
@@ -340,7 +340,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
* As such, when deadlock detection needs to be
* performed the optimistic spinning cannot be done.
*/
- if (ACCESS_ONCE(ww->ctx))
+ if (READ_ONCE(ww->ctx))
break;
}
@@ -348,7 +348,7 @@ static bool mutex_optimistic_spin(struct mutex *lock,
* If there's an owner, wait for it to either
* release the lock or go to sleep.
*/
- owner = ACCESS_ONCE(lock->owner);
+ owner = READ_ONCE(lock->owner);
if (owner && !mutex_spin_on_owner(lock, owner))
break;
@@ -487,7 +487,7 @@ static inline int __sched
__ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
{
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
- struct ww_acquire_ctx *hold_ctx = ACCESS_ONCE(ww->ctx);
+ struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
if (!hold_ctx)
return 0;
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index c112d00..dc85ee2 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -98,7 +98,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
prev = decode_cpu(old);
node->prev = prev;
- ACCESS_ONCE(prev->next) = node;
+ WRITE_ONCE(prev->next, node);
/*
* Normally @prev is untouchable after the above store; because at that
@@ -109,7 +109,7 @@ bool osq_lock(struct optimistic_spin_queue *lock)
* cmpxchg in an attempt to undo our queueing.
*/
- while (!ACCESS_ONCE(node->locked)) {
+ while (!READ_ONCE(node->locked)) {
/*
* If we need to reschedule bail... so we can block.
*/
@@ -148,7 +148,7 @@ unqueue:
* Or we race against a concurrent unqueue()'s step-B, in which
* case its step-C will write us a new @node->prev pointer.
*/
- prev = ACCESS_ONCE(node->prev);
+ prev = READ_ONCE(node->prev);
}
/*
@@ -170,8 +170,8 @@ unqueue:
* it will wait in Step-A.
*/
- ACCESS_ONCE(next->prev) = prev;
- ACCESS_ONCE(prev->next) = next;
+ WRITE_ONCE(next->prev, prev);
+ WRITE_ONCE(prev->next, next);
return false;
}
@@ -193,11 +193,11 @@ void osq_unlock(struct optimistic_spin_queue *lock)
node = this_cpu_ptr(&osq_node);
next = xchg(&node->next, NULL);
if (next) {
- ACCESS_ONCE(next->locked) = 1;
+ WRITE_ONCE(next->locked, 1);
return;
}
next = osq_wait_next(lock, node, NULL);
if (next)
- ACCESS_ONCE(next->locked) = 1;
+ WRITE_ONCE(next->locked, 1);
}
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index e4ad019..06e2214 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -279,7 +279,7 @@ 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 = ACCESS_ONCE(sem->count);
+ long old, count = READ_ONCE(sem->count);
while (true) {
if (!(count == 0 || count == RWSEM_WAITING_BIAS))
@@ -304,9 +304,9 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
return false;
rcu_read_lock();
- owner = ACCESS_ONCE(sem->owner);
+ owner = READ_ONCE(sem->owner);
if (!owner) {
- long count = ACCESS_ONCE(sem->count);
+ long count = READ_ONCE(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
@@ -385,7 +385,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
goto done;
while (true) {
- owner = ACCESS_ONCE(sem->owner);
+ owner = READ_ONCE(sem->owner);
if (owner && !rwsem_spin_on_owner(sem, owner))
break;
@@ -459,7 +459,7 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
/* we're now waiting on the lock, but no longer actively locking */
if (waiting) {
- count = ACCESS_ONCE(sem->count);
+ count = READ_ONCE(sem->count);
/*
* If there were already threads queued before us and there are
diff --git a/lib/lockref.c b/lib/lockref.c
index d2233de..dcab7f5 100644
--- a/lib/lockref.c
+++ b/lib/lockref.c
@@ -18,7 +18,7 @@
#define CMPXCHG_LOOP(CODE, SUCCESS) do { \
struct lockref old; \
BUILD_BUG_ON(sizeof(old) != 8); \
- old.lock_count = ACCESS_ONCE(lockref->lock_count); \
+ old.lock_count = READ_ONCE(lockref->lock_count); \
while (likely(arch_spin_value_unlocked(old.lock.rlock.raw_lock))) { \
struct lockref new = old, prev = old; \
CODE \
--
2.1.4
--
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