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

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Message-Id: <20180830173742.GA17677@linux.vnet.ibm.com>
Date:   Thu, 30 Aug 2018 10:37:42 -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 10:35:09AM -0700, Paul E. McKenney wrote:
> On Thu, Aug 30, 2018 at 12:44:44PM -0400, Steven Rostedt wrote:
> > On Wed, 29 Aug 2018 20:23:15 -0700
> > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > 
> > > > > Glad you like it!  Does it actually work for you?  ;-)  
> > > > 
> > > > Oh, you want me to actually test it too? ;-)  
> > > 
> > > ;-) ;-) ;-)
> > > 
> > > > I'll try to add that in my todo list tomorrow.  
> > > 
> > > Much appreciated!
> > 
> > I reverted the change that prevents calling call_srcu() early:
> > 
> > I checked out v4.19-rc1 and applied these three patches, then did:
> > 
> > git show f8a79d5c7ef47c62d97a30e16064caf2ef91f648 | patch -p1 -R
> > 
> > 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);
 	/* 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. */