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From:   Kalesh Singh <kaleshsingh@google.com>
Date:   Tue, 12 Dec 2023 11:10:44 -0500
Message-ID: <CAC_TJveW=UqdqrDJhDPdY8AmzXtkp+wX8p93MwDFwf=jVzJSwg@mail.gmail.com>
Subject: Re: [PATCH 3/8] rcu/exp: Fix RCU expedited parallel grace period
 kworker allocation failure recovery
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Neeraj Upadhyay <neeraj.upadhyay@amd.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Uladzislau Rezki <urezki@gmail.com>,
        Zqiang <qiang.zhang1211@gmail.com>, rcu <rcu@vger.kernel.org>,
        Anna-Maria Behnsen <anna-maria.behnsen@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>
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On Tue, Dec 12, 2023 at 11:04=E2=80=AFAM Kalesh Singh <kaleshsingh@google.c=
om> wrote:
>
> On Fri, Dec 8, 2023 at 5:06=E2=80=AFPM Frederic Weisbecker <frederic@kern=
el.org> wrote:
> >
> > Under CONFIG_RCU_EXP_KTHREAD=3Dy, the nodes initialization for expedite=
d
> > grace periods is queued to a kworker. However if the allocation of that
> > kworker failed, the nodes initialization is performed synchronously by
> > the caller instead.
> >
> > Now the check for kworker initialization failure relies on the kworker
> > pointer to be NULL while its value might actually encapsulate an
> > allocation failure error.
> >
> > Make sure to handle this case.
> >
> > Fixes: 9621fbee44df ("rcu: Move expedited grace period (GP) work to RT =
kthread_worker")
> > Cc: Kalesh Singh <kaleshsingh@google.com>
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > ---
> >  kernel/rcu/tree.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 82f8130d3fe3..055f4817bc70 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -4723,6 +4723,7 @@ static void __init rcu_start_exp_gp_kworkers(void=
)
> >         rcu_exp_par_gp_kworker =3D kthread_create_worker(0, par_gp_kwor=
ker_name);
> >         if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
> >                 pr_err("Failed to create %s!\n", par_gp_kworker_name);
> > +               rcu_exp_par_gp_kworker =3D NULL;
> >                 kthread_destroy_worker(rcu_exp_gp_kworker);
>
> Hi Frederic,
>
> Thanks for catching this. I think we need to remove the
> kthread_destroy_worker() in this case too.

Ahh sorry, that's the other kworker. LGTM. Thanks.

>
> Otherwise,
>
> Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
>
> --Kalesh
>
> >                 return;
> >         }
> > --
> > 2.42.1
> >