linux-kernel - Re: [PATCH v3] watchdog: initialize device before misc

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Message-ID: <e2b9f886-5a4e-91f3-59d1-c83a46149a82@nokia.com>
Date:   Thu, 16 Jul 2020 13:48:14 +0200
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     "krzysztof.sobota@...ia.com" <krzysztof.sobota@...ia.com>,
        Guenter Roeck <linux@...ck-us.net>, wim@...ux-watchdog.org,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] watchdog: initialize device before misc_register

Hello Krzysztof,

On 16/07/2020 13:32, krzysztof.sobota@...ia.com wrote:
> When watchdog device is being registered, it calls misc_register that
> makes watchdog available for systemd to open. This is a data race
> scenario, because when device is open it may still have device struct
> not initialized - this in turn causes a crash. This patch moves
> device initialization before misc_register call and it solves the
> problem printed below.

[...]

thank you for looking into this!

> Fixes: 72139dfa2464 ("watchdog: Fix the race between the release of watchdog_core_data and cdev")
> Reviewed-by: Guenter Roeck <linux@...ck-us.net>

Reviewed-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>

> Signed-off-by: Krzysztof Sobota <krzysztof.sobota@...ia.com>
> ---
> v1 -> v2:
> * removed Change-Id tag
> * added Review-by tag
> v2 -> v3
> * convert spaces to tabs
> * convert (hopefully) mail to plaintext
> ---
>  drivers/watchdog/watchdog_dev.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
> index 10b2090f3e5e..1c322caecf7f 100644
> --- a/drivers/watchdog/watchdog_dev.c
> +++ b/drivers/watchdog/watchdog_dev.c
> @@ -947,6 +947,15 @@ static int watchdog_cdev_register(struct watchdog_device *wdd)
> 	if (IS_ERR_OR_NULL(watchdog_kworker))
> 		return -ENODEV;
> 
> +	device_initialize(&wd_data->dev);
> +	wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id);
> +	wd_data->dev.class = &watchdog_class;
> +	wd_data->dev.parent = wdd->parent;
> +	wd_data->dev.groups = wdd->groups;
> +	wd_data->dev.release = watchdog_core_data_release;
> +	dev_set_drvdata(&wd_data->dev, wdd);
> +	dev_set_name(&wd_data->dev, "watchdog%d", wdd->id);
> +
> 	kthread_init_work(&wd_data->work, watchdog_ping_work);
> 	hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> 	wd_data->timer.function = watchdog_timer_expired;
> @@ -967,15 +976,6 @@ static int watchdog_cdev_register(struct watchdog_device *wdd)
> 		}
> 	}
> 
> -	device_initialize(&wd_data->dev);
> -	wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id);
> -	wd_data->dev.class = &watchdog_class;
> -	wd_data->dev.parent = wdd->parent;
> -	wd_data->dev.groups = wdd->groups;
> -	wd_data->dev.release = watchdog_core_data_release;
> -	dev_set_drvdata(&wd_data->dev, wdd);
> -	dev_set_name(&wd_data->dev, "watchdog%d", wdd->id);
> -
> 	/* Fill in the data structures */
> 	cdev_init(&wd_data->cdev, &watchdog_fops);
> 
> --
> 2.14.0
> 

-- 
Best regards,
Alexander Sverdlin.