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Date: Tue, 6 Jan 2015 11:45:08 -0800
From: Davidlohr Bueso <dave@...olabs.net>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Davidlohr Bueso <dave@...olabs.net>,
linux-kernel@...r.kernel.org,
Christian Borntraeger <borntraeger@...ibm.com>,
Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 5/6] locking: Use [READ,ASSIGN]_ONCE() for non-scalar types
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).
Change the generic locking code to replace ACCESS_ONCE with the
new calls. I guess everyone will eventually have to update, so
lets see what happens; we also become the first users of ASSIGN_ONCE.
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
---
kernel/locking/mcs_spinlock.h | 6 +++---
kernel/locking/mutex.c | 8 ++++----
kernel/locking/osq_lock.c | 8 ++++----
kernel/locking/rwsem-xadd.c | 4 ++--
4 files changed, 13 insertions(+), 13 deletions(-)
diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index d1fe2ba..903009a 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;
+ ASSIGN_ONCE(node, prev->next);
/* 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 2ac48e0..0082705 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -269,7 +269,7 @@ 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();
@@ -343,7 +343,7 @@ 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;
}
@@ -351,7 +351,7 @@ 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;
@@ -490,7 +490,7 @@ 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 ec83d4d..9c6e251 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;
+ ASSIGN_ONCE(node, prev->next);
/*
* Normally @prev is untouchable after the above store; because at that
@@ -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;
+ ASSIGN_ONCE(prev, next->prev);
+ ASSIGN_ONCE(next, prev->next);
return false;
}
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 7628c3f..2e651f6 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -294,7 +294,7 @@ 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)
on_cpu = owner->on_cpu;
rcu_read_unlock();
@@ -359,7 +359,7 @@ 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;
--
2.1.2
--
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