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Message-ID: <20210402005813.GE116405@lothringen>
Date: Fri, 2 Apr 2021 02:58:13 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: "Paul E. McKenney" <paulmck@...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?
call_srcu() -> __call_srcu() -> srcu_gp_start_if_needed() ->
check_init_srcu_struct() ?
Or is it me missing something?
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