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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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180518165534.GA22348@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov 2018-05-18 18:55:35 +02:00 committed by Ingo Molnar
parent 675c00c332
commit 1b22fc609c
1 changed files with 13 additions and 12 deletions
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25
kernel/locking/rwsem-xadd.c
View File

@ -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;
}