Re: [PATCH 5/5] locking/percpu-rwsem: Remove the embedded rwsem

[Peter Zijlstra]

On Mon, Nov 18, 2019 at 11:53:04AM -0800, Davidlohr Bueso wrote:
> On Wed, 13 Nov 2019, Peter Zijlstra wrote:
> > @@ -54,23 +52,23 @@ static bool __percpu_down_read_trylock(s
> > 	 * the same CPU as the increment, avoiding the
> > 	 * increment-on-one-CPU-and-decrement-on-another problem.
> 
> Nit: Now that you've made read_count more symmetric, maybe this first
> paragraph can be moved down to __percpu_rwsem_trylock() reader side,
> as such:
> 
> 	/*
> 	 * Due to having preemption disabled the decrement happens on
> 	 * the same CPU as the increment, avoiding the
> 	 * increment-on-one-CPU-and-decrement-on-another problem.
> 	 */
> 	preempt_disable();
> 	ret = __percpu_down_read_trylock(sem);
> 	preempt_enable();

There's another callsite for that function too, so I think the current
place still works best.