linux-kernel - Re: [PATCH] driver core: Fix uevent

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Message-ID: <dfcb0456-dd75-4b9f-9cc8-f0658cd9ce29@I-love.SAKURA.ne.jp>
Date: Sat, 13 Jul 2024 07:18:41 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Dan Williams <dan.j.williams@...el.com>, gregkh@...uxfoundation.org
Cc: syzbot+4762dd74e32532cda5ff@...kaller.appspotmail.com,
        stable@...r.kernel.org, Ashish Sangwan <a.sangwan@...sung.com>,
        Namjae Jeon <namjae.jeon@...sung.com>,
        Dirk Behme <dirk.behme@...bosch.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-kernel@...r.kernel.org,
        linux-cxl@...r.kernel.org
Subject: Re: [PATCH] driver core: Fix uevent_show() vs driver detach race

On 2024/07/13 4:42, Dan Williams wrote:
> @@ -2668,8 +2670,12 @@ static int dev_uevent(const struct kobject *kobj, struct kobj_uevent_env *env)
>  	if (dev->type && dev->type->name)
>  		add_uevent_var(env, "DEVTYPE=%s", dev->type->name);
>  
> -	if (dev->driver)
> -		add_uevent_var(env, "DRIVER=%s", dev->driver->name);
> +	/* Synchronize with module_remove_driver() */
> +	rcu_read_lock();
> +	driver = READ_ONCE(dev->driver);
> +	if (driver)
> +		add_uevent_var(env, "DRIVER=%s", driver->name);
> +	rcu_read_unlock();
>  

Given that read of dev->driver is protected using RCU,

> @@ -97,6 +98,9 @@ void module_remove_driver(struct device_driver *drv)
>  	if (!drv)
>  		return;
>  

where is

	dev->driver = NULL;

performed prior to

> +	/* Synchronize with dev_uevent() */
> +	synchronize_rcu();
> +

this synchronize_rcu(), in order to make sure that
READ_ONCE(dev->driver) in dev_uevent() observes NULL?

>  	sysfs_remove_link(&drv->p->kobj, "module");
>  
>  	if (drv->owner)
>