linux-kernel - Re: [PATCH] rcu/tree: Force quiescent state on callback overload

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Message-ID: <20200623162939.GJ9247@paulmck-ThinkPad-P72>
Date:   Tue, 23 Jun 2020 09:29:39 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     Neeraj Upadhyay <neeraju@...eaurora.org>, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rcu/tree: Force quiescent state on callback overload

On Tue, Jun 23, 2020 at 11:42:14AM -0400, Joel Fernandes wrote:
> On Mon, Jun 22, 2020 at 12:07:27AM +0530, Neeraj Upadhyay wrote:
> > On callback overload, we want to force quiescent state immediately,
> > for the first and second fqs. Enforce the same, by including
> > RCU_GP_FLAG_OVLD flag, in fqsstart check.
> > 
> > Signed-off-by: Neeraj Upadhyay <neeraju@...eaurora.org>
> > ---
> 
> Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> 
> And I think needs fixes tag:
> Fixes: 1fca4d12f4637 ("rcu: Expedite first two FQS scans under callback-overload conditions")

Excellent, both applied, thank you!

					Thanx, Paul

> thanks,
> 
>  - Joel
> 
> 
> >  kernel/rcu/tree.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index d0988a1..6226bfb 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1865,7 +1865,7 @@ static void rcu_gp_fqs_loop(void)
> >  			break;
> >  		/* If time for quiescent-state forcing, do it. */
> >  		if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
> > -		    (gf & RCU_GP_FLAG_FQS)) {
> > +		    (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
> >  			trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
> >  					       TPS("fqsstart"));
> >  			rcu_gp_fqs(first_gp_fqs);
> > -- 
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> > a Linux Foundation Collaborative Project
> >