linux-kernel - Re: [PATCH tip/core/rcu 3/3] srcu: Make early-boot call

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Date:   Thu, 30 Aug 2018 16:12:11 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH tip/core/rcu 3/3] srcu: Make early-boot call_srcu() reuse
 workqueue lists

On Thu, Aug 30, 2018 at 02:36:17PM -0400, Steven Rostedt wrote:
> On Thu, 30 Aug 2018 10:37:42 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> 
> > > > But still triggered the following:
> > > > 
> > > >  WARNING: CPU: 0 PID: 0 at /work/git/linux-trace.git/kernel/rcu/srcutree.c:242 check_init_srcu_struct+0x85/0x90  
> > > 
> > > Gah!!!  I needed to have removed that WARN_ON_ONCE(), didn't I?
> > > In fact, I should have removed that once I started using workqueues,
> > > quite some time back.  
> > 
> > As in the below patch.
> > 
> > 							Thanx, Paul
> > 
> > ------------------------------------------------------------------------
> > 
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 75571ff09c62..a8846ed7f352 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -239,7 +239,6 @@ static void check_init_srcu_struct(struct srcu_struct *sp)
> >  {
> >  	unsigned long flags;
> >  
> > -	WARN_ON_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INIT);
> 
> Well it boots without warning ;-)
> 
> Tested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

Thank you again!  I applied this to 1/3 and 3/3 on the assumption that
you did not run rcutorture.  ;-)

							Thanx, Paul

> -- Steve
> 
> >  	/* The smp_load_acquire() pairs with the smp_store_release(). */
> >  	if (!rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq_needed))) /*^^^*/
> >  		return; /* Already initialized. */
>