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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>
This commit is contained in:
Waiman Long 2016-05-17 21:26:23 -04:00 committed by Ingo Molnar
parent bf7b4c472d
commit ddd0fa73c2
1 changed files with 20 additions and 18 deletions
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38
kernel/locking/rwsem-xadd.c
View File

@ -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;
/*