linux-kernel - Re: [PATCH 1/3] srcu: Remove superfluous ssp initialization on deferred work queue

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Date:   Thu, 1 Apr 2021 18:01:21 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Josh Triplett <josh@...htriplett.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 1/3] srcu: Remove superfluous ssp initialization on
 deferred work queue

On Thu, Apr 01, 2021 at 05:48:56PM -0700, Paul E. McKenney wrote:
> On Fri, Apr 02, 2021 at 01:47:02AM +0200, Frederic Weisbecker wrote:
> > When an ssp has already started a grace period and queued an early work
> > to flush after SRCU workqueues are created, we expect the ssp to be
> > properly initialized already. So we can skip this step at this stage.
> > 
> > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Lai Jiangshan <jiangshanlai@...il.com>
> > Cc: Neeraj Upadhyay <neeraju@...eaurora.org>
> > Cc: Josh Triplett <josh@...htriplett.org>
> > Cc: Joel Fernandes <joel@...lfernandes.org>
> > Cc: Uladzislau Rezki <urezki@...il.com>
> > ---
> >  kernel/rcu/srcutree.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 036ff5499ad5..7197156418e4 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -1396,7 +1396,6 @@ void __init srcu_init(void)
> >  	while (!list_empty(&srcu_boot_list)) {
> >  		ssp = list_first_entry(&srcu_boot_list, struct srcu_struct,
> >  				      work.work.entry);
> > -		check_init_srcu_struct(ssp);
> 
> You lost me on this one.  What happens if the only pre-initialization
> invocation on the statically allocated srcu_struct pointed to by ssp
> was call_srcu()?  I am not seeing how the initialization has already
> happened in that case.
> 
> What am I missing here?

Idiot here was looking at Tiny SRCU's call_srcu(), not that of Tree SRCU.
Never mind, I will queue this one as well.

							Thanx, Paul

> >  		list_del_init(&ssp->work.work.entry);
> >  		queue_work(rcu_gp_wq, &ssp->work.work);
> >  	}
> > -- 
> > 2.25.1
> >