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

[Neeraj Upadhyay]

Hi Paul,

On 6/22/2020 1:20 AM, Paul E. McKenney 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@xxxxxxxxxxxxxx>
>
> Good catch!
>
> But what did you do to verify that this change does the right thing?
>
> 						Thanx, Paul

I haven't done a runtime verification of this code path; I posted this, 
based on review of this code.


Thanks
Neeraj

> > ---
> >   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

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