linux-kernel - Re: [PATCH RFC] srcu: Yet more detail for srcu_readers_active_idx

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Date:   Wed, 14 Dec 2022 23:10:43 +0000
From:   Joel Fernandes <joel@...lfernandes.org>
To:     paulmck@...nel.org
Cc:     boqun.feng@...il.com, frederic@...nel.org, neeraj.iitr10@...il.com,
        urezki@...il.com, rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] srcu: Yet more detail for srcu_readers_active_idx_check()
 comments

On Wed, Dec 14, 2022 at 11:07 PM Joel Fernandes <joel@...lfernandes.org> wrote:
>
> On Wed, Dec 14, 2022 at 9:24 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> > > I also did not get why you care about readers that come and ago (you
> > > mentioned the first reader seeing incorrect idx and the second reader
> > > seeing the right flipped one, etc). Those readers are irrelevant
> > > AFAICS since they came and went, and need not be waited on , right?.
> >
> > The comment is attempting to show (among other things) that we don't
> > need to care about readers that come and go more than twice during that
> > critical interval of time during the counter scans.
>
> Why do we need to care about readers that come and go even once? Once
> they are gone, they have already done an unlock() and their RSCS is
> over, so they need to be considered AFAICS.
>

Aargh, I meant: "so they need to be considered AFAICS".

Thanks.