linux-kernel - Re: [PATCH] device property: Track owner device of device property

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Date:   Fri, 20 Oct 2017 16:34:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Lukas Wunner <lukas@...ner.de>, stable@...r.kernel.org
Subject: Re: [PATCH] device property: Track owner device of device property

On Mon, Oct 09, 2017 at 04:28:37PM +0300, Jarkko Nikula wrote:
> Deletion of subdevice will remove device properties associated to parent
> when they share the same firmware node after commit 478573c93abd ("driver
> core: Don't leak secondary fwnode on device removal"). This was observed
> with a driver adding subdevice that driver wasn't able to read device
> properties after rmmod/modprobe cycle.
> 
> Consider the lifecycle of it:
> 
> parent device registration
> 	ACPI_COMPANION_SET()
> 	device_add_properties()
> 		pset_copy_set()
> 		set_secondary_fwnode(dev, &p->fwnode)
> 	device_add()
> 
> parent probe
> 	read device properties
> 	ACPI_COMPANION_SET(subdevice, ACPI_COMPANION(parent))
> 	device_add(subdevice)
> 
> parent remove
> 	device_del(subdevice)
> 		device_remove_properties()
> 			set_secondary_fwnode(dev, NULL);
> 			pset_free()
> 
> Parent device will have its primary firmware node pointing to an ACPI node
> and secondary firmware node point to device properties.
> ACPI_COMPANION_SET() call in parent probe will set the subdevice's firmware
> node to point to the same 'struct fwnode_handle' and the associated
> secondary firmware node, i.e. the device properties as the parent.
> 
> When subdevice is deleted in parent remove that will remove those device
> properties and attempt to read device properties in next parent probe call
> will fail.
> 
> Fix this by tracking the owner device of device properties and delete them
> only when owner device is being deleted.
> 
> Fixes: 478573c93abd ("driver core: Don't leak secondary fwnode on device removal")
> Cc: <stable@...r.kernel.org> # v4.9+
> Signed-off-by: Jarkko Nikula <jarkko.nikula@...ux.intel.com>
> ---
>  drivers/base/property.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index d0b65bbe7e15..21fcc13013a5 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -21,6 +21,7 @@
>  #include <linux/phy.h>
>  
>  struct property_set {
> +	struct device *dev;
>  	struct fwnode_handle fwnode;
>  	const struct property_entry *properties;
>  };
> @@ -891,6 +892,7 @@ static struct property_set *pset_copy_set(const struct property_set *pset)
>  void device_remove_properties(struct device *dev)
>  {
>  	struct fwnode_handle *fwnode;
> +	struct property_set *pset;
>  
>  	fwnode = dev_fwnode(dev);
>  	if (!fwnode)
> @@ -900,16 +902,16 @@ void device_remove_properties(struct device *dev)
>  	 * the pset. If there is no real firmware node (ACPI/DT) primary
>  	 * will hold the pset.
>  	 */
> -	if (is_pset_node(fwnode)) {
> +	pset = to_pset_node(fwnode);
> +	if (pset) {
>  		set_primary_fwnode(dev, NULL);
> -		pset_free_set(to_pset_node(fwnode));
>  	} else {
> -		fwnode = fwnode->secondary;
> -		if (!IS_ERR(fwnode) && is_pset_node(fwnode)) {
> +		pset = to_pset_node(fwnode->secondary);
> +		if (pset && dev == pset->dev)
>  			set_secondary_fwnode(dev, NULL);
> -			pset_free_set(to_pset_node(fwnode));
> -		}
>  	}
> +	if (pset && dev == pset->dev)
> +		pset_free_set(pset);
>  }
>  EXPORT_SYMBOL_GPL(device_remove_properties);
>  
> @@ -938,6 +940,7 @@ int device_add_properties(struct device *dev,
>  
>  	p->fwnode.ops = &pset_fwnode_ops;
>  	set_secondary_fwnode(dev, &p->fwnode);
> +	p->dev = dev;

Don't you also need to increment the reference counter here?  Or how is
it assured that it will not go away?

thanks,

greg k-h