Re: [PATCH V8 5/8] percpu-refcount: introduce __percpu_ref_tryget_live

[Tejun Heo <tj@kernel.org>]

Hello,

On Wed, Oct 04, 2017 at 03:20:40AM +0800, Ming Lei wrote:
> On Tue, Oct 03, 2017 at 07:14:59AM -0700, Tejun Heo wrote:
> > Hello,
> > 
> > On Tue, Oct 03, 2017 at 10:04:03PM +0800, Ming Lei wrote:
> > > Block layer need to call this function after holding
> > > rcu lock in a real hot path, so introduce this helper.
> > 
> > The patch description is too anemic.  It doesn't even describe what
> > changes are being made, let alone justifying them.
> 
> Sorry for Cc you, and this change is needed by the following
> patch:
> 
> 	https://marc.info/?l=linux-scsi&m=150703956929333&w=2
> 
> Block layer need to call percpu_ref_tryget_live()
> with holding RCU read lock, given it is a hot I/O
> path, that is why I make this patch so that we can
> avoid nested RCU read lock and save a bit cost.

I'm not necessarily against it but please name it sth like
percpu_ref_tryget_live_locked(), add lockdep assertions in the inner
function and document properly.

Thanks.

-- 
tejun