Commit 1b22fc60 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

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: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarWaiman 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: default avatarIngo Molnar <mingo@kernel.org>
parent 675c00c3

kernel/locking/rwsem-xadd.c

+13 −12
Original line number Diff line number Diff line
@@ -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;

		}

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