Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <1570927586-12023-1-git-send-email-zhenzhong.duan@oracle.com>
In-Reply-To: <1570927586-12023-1-git-send-email-zhenzhong.duan@oracle.com>
From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Tue, 22 Oct 2019 18:35:31 +0200
Message-ID: <CAJZ5v0iaWxu1vL08zyEfx6_Eku9yK5kh-HK4ZdbBtqZvSVd6tw@mail.gmail.com>
Subject: Re: [PATCH] cpuidle: not unset the driver if it already exist
To:     Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Marcelo Tosatti <mtosatti@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, Oct 14, 2019 at 2:43 AM Zhenzhong Duan
<zhenzhong.duan@oracle.com> wrote:
>
> __cpuidle_set_driver() check if there is an already exist driver and
> unset it before return with -EBUSY. The next call will succeed as it's
> just unset. This is strange as we should either keep old driver and
> return -EBUSY or unset and set new driver and return 0.
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> ---
>  drivers/cpuidle/driver.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
> index 80c1a83..a200304 100644
> --- a/drivers/cpuidle/driver.c
> +++ b/drivers/cpuidle/driver.c
> @@ -74,7 +74,6 @@ static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
>         for_each_cpu(cpu, drv->cpumask) {
>
>                 if (__cpuidle_get_cpu_driver(cpu)) {
> -                       __cpuidle_unset_driver(drv);
>                         return -EBUSY;
>                 }

There is a bug here, but it needs to be fixed differently.

The function should check if any of the CPUs in the mask have a driver
(which is different from drv) already and if so return -EBUSY before
updating any cpuidle_drivers per-CPU pointers.