linux-kernel - Re: [PATCH 2/2] rcu/tree: Clarify comments about FQS loop reporting quiescent states

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Date:   Thu, 30 Jul 2020 21:21:52 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        rcu <rcu@...r.kernel.org>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/2] rcu/tree: Clarify comments about FQS loop reporting
 quiescent states

On Thu, Jul 30, 2020 at 09:35:20AM -0700, Paul E. McKenney wrote:
> On Wed, Jul 29, 2020 at 11:25:19PM -0400, Joel Fernandes wrote:
> > On Wed, Jul 29, 2020 at 11:02 PM Joel Fernandes (Google)
> > <joel@...lfernandes.org> wrote:
> > >
> > > At least since v4.19, the FQS loop no longer reports quiescent states
> > 
> > I meant here, "FQS loop no longer reports quiescent states for offline CPUs."
> > 
> > Sorry,
> 
> You did have me going there for a bit.  ;-)
> 
> No period (".") at the end though, unless you fix up the following
> to start a new sentence.

Ok.

> > > unless it is a dire situation where an offlined CPU failed to report
> > > a quiescent state. Let us clarify the comment in rcu_gp_init() inorder
> > > to keep the comment current.
> 
> How about the following for this last sentence?
> 
> "This commit therefore fixes the comment in rcu_gp_init() to match
> the current code."

As per:
https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html

It says:
Describe your changes in imperative mood, e.g. “make xyzzy do frotz” instead
of “[This patch] makes xyzzy do frotz” or “[I] changed xyzzy to do frotz”, as
if you are giving orders to the codebase to change its behaviour.

May be I should make it "Fix the comment in rcu_gp_init() to match the
current code"?

> > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > ---
> > >  kernel/rcu/tree.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 1e51962b565b..929568ff5989 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -1701,8 +1701,8 @@ static bool rcu_gp_init(void)
> > >
> > >         /*
> > >          * Apply per-leaf buffered online and offline operations to the
> > > -        * rcu_node tree.  Note that this new grace period need not wait
> > > -        * for subsequent online CPUs, and that quiescent-state forcing
> > > +        * rcu_node tree.  Note that this new grace period need not wait for
> > > +        * subsequent online CPUs, and that RCU hooks in CPU offlining path
> > >          * will handle subsequent offline CPUs.
> 
> How about something like this?
> 
> 	...  Note that this new grace period ned not wait for subsequent
> 	online CPUs, and that RCU hooks in the CPU offlining path, when
> 	combined with checks in this function, will handle CPUs that
> 	are currently going offline and that go offline later.

Sounds good to me. I think s/and that go/or that go/ though.

I will make these changes and send v3, let me know though if you object.

thanks,

 - Joel


> 						Thanx, Paul
> 
> > >          */
> > >         rcu_state.gp_state = RCU_GP_ONOFF;
> > > --
> > > 2.28.0.rc0.142.g3c755180ce-goog
> > >