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authorWaiman Long <Waiman.Long@hpe.com>2016-05-17 21:26:23 -0400
committerIngo Molnar <mingo@kernel.org>2016-06-08 15:17:00 +0200
commitddd0fa73c2b71c35de4fe7ae60a5f1a6cddc2cf0 (patch)
tree6ff6f3e9c5f3b7866ceb0d1608e49ce6f4c90043 /kernel/locking
parentbf7b4c472db44413251bcef79ca1f6bf1ec81475 (diff)
locking/rwsem: Streamline the rwsem_optimistic_spin() code
This patch moves the owner loading and checking code entirely inside of rwsem_spin_on_owner() to simplify the logic of rwsem_optimistic_spin() loop. Suggested-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Waiman Long <Waiman.Long@hpe.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Peter Hurley <peter@hurleysoftware.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Douglas Hatch <doug.hatch@hpe.com> Cc: Jason Low <jason.low2@hp.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott J Norton <scott.norton@hpe.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1463534783-38814-6-git-send-email-Waiman.Long@hpe.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rwsem-xadd.c38
1 files changed, 20 insertions, 18 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 4f1daf5a472d..2031281bb940 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -350,9 +350,16 @@ done:
return ret;
}
-static noinline
-bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
+/*
+ * 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) {
/*
@@ -372,7 +379,7 @@ bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
cpu_relax_lowlatency();
}
rcu_read_unlock();
-
+out:
/*
* If there is a new owner or the owner is not set, we continue
* spinning.
@@ -382,7 +389,6 @@ bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner)
static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
{
- struct task_struct *owner;
bool taken = false;
preempt_disable();
@@ -394,21 +400,17 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
if (!osq_lock(&sem->osq))
goto done;
- while (true) {
- owner = READ_ONCE(sem->owner);
+ /*
+ * 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)) {
/*
- * Don't spin if
- * 1) the owner is a reader as we we can't determine if the
- * reader is actively running or not.
- * 2) The rwsem_spin_on_owner() returns false which means
- * the owner isn't running.
+ * Try to acquire the lock
*/
- if (rwsem_owner_is_reader(owner) ||
- (rwsem_owner_is_writer(owner) &&
- !rwsem_spin_on_owner(sem, owner)))
- break;
-
- /* wait_lock will be acquired if write_lock is obtained */
if (rwsem_try_write_lock_unqueued(sem)) {
taken = true;
break;
@@ -420,7 +422,7 @@ static bool rwsem_optimistic_spin(struct rw_semaphore *sem)
* we're an RT task that will live-lock because we won't let
* the owner complete.
*/
- if (!owner && (need_resched() || rt_task(current)))
+ if (!sem->owner && (need_resched() || rt_task(current)))
break;
/*