Re: [PATCH v2] usb: roles: Call try_module_get() from usb_role_switch_find_by_fwnode()

From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
To: Hans de Goede <hdegoede@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guenter Roeck <linux@roeck-us.net>,
	linux-usb@vger.kernel.org
Subject: Re: [PATCH v2] usb: roles: Call try_module_get() from usb_role_switch_find_by_fwnode()
Date: Fri, 9 Apr 2021 16:07:13 +0300	[thread overview]
Message-ID: <YHBRgfysBCsRbRIr@kuha.fi.intel.com> (raw)
In-Reply-To: <20210409124136.65591-1-hdegoede@redhat.com>

On Fri, Apr 09, 2021 at 02:41:36PM +0200, Hans de Goede wrote:
> usb_role_switch_find_by_fwnode() returns a reference to the role-switch
> which must be put by calling usb_role_switch_put().
> 
> usb_role_switch_put() calls module_put(sw->dev.parent->driver->owner),
> add a matching try_module_get() to usb_role_switch_find_by_fwnode(),
> making it behave the same as the other usb_role_switch functions
> which return a reference.
> 
> This avoids a WARN_ON being hit at kernel/module.c:1158 due to the
> module-refcount going below 0.
> 
> Fixes: c6919d5e0cd1 ("usb: roles: Add usb_role_switch_find_by_fwnode()")
> Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>

> ---
> Changes in v2:
> - Fix typo in Subject
> - Add Fixes tag
> ---
>  drivers/usb/roles/class.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/roles/class.c b/drivers/usb/roles/class.c
> index 97f37077b7f9..33b637d0d8d9 100644
> --- a/drivers/usb/roles/class.c
> +++ b/drivers/usb/roles/class.c
> @@ -189,6 +189,8 @@ usb_role_switch_find_by_fwnode(const struct fwnode_handle *fwnode)
>  		return NULL;
>  
>  	dev = class_find_device_by_fwnode(role_class, fwnode);
> +	if (dev)
> +		WARN_ON(!try_module_get(dev->parent->driver->owner));
>  
>  	return dev ? to_role_switch(dev) : NULL;
>  }
> -- 
> 2.30.2

thanks,

-- 
heikki