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References: <20231208220545.7452-1-frederic@kernel.org> <20231208220545.7452-4-frederic@kernel.org>
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From:   Kalesh Singh <kaleshsingh@google.com>
Date:   Tue, 12 Dec 2023 11:04:13 -0500
Message-ID: <CAC_TJvcODXd71icqTLs5fkCKswML5huK-2V2=R2-D9-Fc0R1MA@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 Fri, Dec 8, 2023 at 5:06=E2=80=AFPM Frederic Weisbecker <frederic@kernel=
.org> wrote:
>
> Under CONFIG_RCU_EXP_KTHREAD=3Dy, the nodes initialization for expedited
> 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 kt=
hread_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_kworke=
r_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.

Otherwise,

Reviewed-by: Kalesh Singh <kaleshsingh@google.com>

--Kalesh

>                 return;
>         }
> --
> 2.42.1
>