On 05/18/2018 12:55 PM, Oleg Nesterov wrote: > 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 <[email protected]> > --- > 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; > }
Acked-by: Waiman Long <[email protected]>
