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Subject[PATCH] locking/rwsem: simplify the is-owner-spinnable checks
Add the trivial owner_on_cpu() helper for rwsem_can_spin_on_owner() and
rwsem_spin_on_owner(), it also allows to make rwsem_can_spin_on_owner()
a bit more clear.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/locking/rwsem-xadd.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a903367..3064c50 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -347,6 +347,15 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
}
}

+static inline bool owner_on_cpu(struct task_struct *owner)
+{
+ /*
+ * As lock holder preemption issue, we both skip spinning if
+ * task is not on cpu or its cpu is preempted
+ */
+ return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
+}
+
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
@@ -359,17 +368,10 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)

rcu_read_lock();
owner = READ_ONCE(sem->owner);
- if (!owner || !is_rwsem_owner_spinnable(owner)) {
- ret = !owner; /* !owner is spinnable */
- goto done;
+ if (owner) {
+ ret = is_rwsem_owner_spinnable(owner) &&
+ owner_on_cpu(owner);
}
-
- /*
- * As lock holder preemption issue, we both skip spinning if task is not
- * on cpu or its cpu is preempted
- */
- ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
-done:
rcu_read_unlock();
return ret;
}
@@ -398,8 +400,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
* abort spinning when need_resched or owner is not running or
* owner's cpu is preempted.
*/
- if (!owner->on_cpu || need_resched() ||
- vcpu_is_preempted(task_cpu(owner))) {
+ if (need_resched() || !owner_on_cpu(owner)) {
rcu_read_unlock();
return false;
}
--
2.5.0

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