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From:   "Zhang, Qiang1" <qiang1.zhang@intel.com>
To:     "paulmck@kernel.org" <paulmck@kernel.org>,
        Mukesh Ojha <quic_mojha@quicinc.com>
CC:     "frederic@kernel.org" <frederic@kernel.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] rcu: Add rnp->expmask output to show_rcu_gp_kthreads()
Thread-Topic: [PATCH] rcu: Add rnp->expmask output to show_rcu_gp_kthreads()
Thread-Index: AQHYb/JC2wviYb3eD0WoVIBYSpjWx60vCIGAgACYBACAAAnG8A==
Date:   Wed, 25 May 2022 14:42:41 +0000
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On Wed, May 25, 2022 at 10:29:23AM +0530, Mukesh Ojha wrote:
>=20
>=20
> On 5/25/2022 10:15 AM, Zqiang wrote:
> > Currently, for expedited rcu we only check 'rnp->exp_tasks', however=20
> > the 'rnp->exp_tasks' are not always exist for expedited grace period=20
> > that not end. this commit add 'rnp->expmask' condition.
> >=20
> > Signed-off-by: Zqiang <qiang1.zhang@intel.com>
>=20
> Thanks !! for the patch.
> Commit log could require wordsmith from Paul :-)

>For Paul to wordsmith this commit log, he must first understand why this c=
hange is useful, keeping in mind that show_rcu_gp_kthreads() is invoked for=
 normal grace periods, but not for expedited ones.
>
>The point of ->exp_mask for debugging forward-progress issues for normal g=
race periods is to understand why tasks blocking the current normal grace p=
eriod are not yet being boosted (because the expedited grace period's boost=
ing takes precedence).  How do these additions help you?

Hi Paul

Oh sorry, I misunderstood, my previous understanding was only to get the st=
atus of the current grace period.
thank you for the explanation.

Thanks
Zqiang=20

>
>(Not saying that they cannot possibly help you.  I am instead saying that =
you must tell me how they have helped you guys.)
>
>							Thanx, Paul

> Reviewed-by: quic_mojha@quicinc.com
>=20
> -Mukesh
>=20
> > ---
> >   kernel/rcu/tree_stall.h | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >=20
> > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index=20
> > 2464b0eccfd0..5c4df855f2ac 100644
> > --- a/kernel/rcu/tree_stall.h
> > +++ b/kernel/rcu/tree_stall.h
> > @@ -865,13 +865,15 @@ void show_rcu_gp_kthreads(void)
> >   	rcu_for_each_node_breadth_first(rnp) {
> >   		if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rnp->gp_seq=
_needed)) &&
> >   		    !data_race(READ_ONCE(rnp->qsmask)) && !data_race(READ_ONCE(rnp-=
>boost_tasks)) &&
> > -		    !data_race(READ_ONCE(rnp->exp_tasks)) && !data_race(READ_ONCE(rn=
p->gp_tasks)))
> > +		    !data_race(READ_ONCE(rnp->expmask)) && !data_race(READ_ONCE(rnp-=
>exp_tasks)) &&
> > +			!data_race(READ_ONCE(rnp->gp_tasks)))
> >   			continue;
> > -		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask =
%#lx %c%c%c%c ->n_boosts %ld\n",
> > +		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld=20
> > +->qsmask %#lx ->expmask %#lx %c%c%c%c ->n_boosts %ld\n",
> >   			rnp->grplo, rnp->grphi,
> >   			(long)data_race(READ_ONCE(rnp->gp_seq)),
> >   			(long)data_race(READ_ONCE(rnp->gp_seq_needed)),
> >   			data_race(READ_ONCE(rnp->qsmask)),
> > +			data_race(READ_ONCE(rnp->expmask)),
> >   			".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))],
> >   			".B"[!!data_race(READ_ONCE(rnp->boost_tasks))],
> >   			".E"[!!data_race(READ_ONCE(rnp->exp_tasks))],