Re: [PATCH 5/8] staging: vme: add functions for bridge module refcounting

[Martyn Welch]

On 01/08/11 11:20, Manohar Vanga wrote:
> This patch adds functions that allow for reference counting
> bridge modules. The patch introduces the functions
> 'vme_bridge_get()' and 'vme_bridge_put()'.
> 
> This patch is based on the changes introduced by Emilio G. Cota
> in the patch:
> 
>     https://lkml.org/lkml/2010/10/25/492
> 
> Signed-off-by: Manohar Vanga <manohar.vanga@xxxxxxx>
> ---
>  drivers/staging/vme/bridges/vme_ca91cx42.c |    2 +
>  drivers/staging/vme/bridges/vme_tsi148.c   |    2 +
>  drivers/staging/vme/devices/vme_user.c     |   20 +++++++++++
>  drivers/staging/vme/vme.c                  |   48 ++++++++++++++++++++++++++++
>  drivers/staging/vme/vme.h                  |    2 +
>  drivers/staging/vme/vme_bridge.h           |    1 +
>  6 files changed, 75 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/staging/vme/bridges/vme_ca91cx42.c b/drivers/staging/vme/bridges/vme_ca91cx42.c
> index 15a0b19..2f9c22b 100644
> --- a/drivers/staging/vme/bridges/vme_ca91cx42.c
> +++ b/drivers/staging/vme/bridges/vme_ca91cx42.c
> @@ -1680,6 +1680,8 @@ static int ca91cx42_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	ca91cx42_bridge->parent = &pdev->dev;
>  	strcpy(ca91cx42_bridge->name, driver_name);
>  
> +	ca91cx42_bridge->owner = THIS_MODULE;
> +
>  	/* Setup IRQ */
>  	retval = ca91cx42_irq_init(ca91cx42_bridge);
>  	if (retval != 0) {
> diff --git a/drivers/staging/vme/bridges/vme_tsi148.c b/drivers/staging/vme/bridges/vme_tsi148.c
> index 5c147d6..9db89dc 100644
> --- a/drivers/staging/vme/bridges/vme_tsi148.c
> +++ b/drivers/staging/vme/bridges/vme_tsi148.c
> @@ -2320,6 +2320,8 @@ static int tsi148_probe(struct pci_dev *pdev, const struct pci_device_id *id)
>  	tsi148_bridge->parent = &pdev->dev;
>  	strcpy(tsi148_bridge->name, driver_name);
>  
> +	tsi148_bridge->owner = THIS_MODULE;
> +
>  	/* Setup IRQ */
>  	retval = tsi148_irq_init(tsi148_bridge);
>  	if (retval != 0) {
> diff --git a/drivers/staging/vme/devices/vme_user.c b/drivers/staging/vme/devices/vme_user.c
> index 3cbeb2a..7ed4a5c 100644
> --- a/drivers/staging/vme/devices/vme_user.c
> +++ b/drivers/staging/vme/devices/vme_user.c
> @@ -118,6 +118,8 @@ static struct cdev *vme_user_cdev;		/* Character device */
>  static struct class *vme_user_sysfs_class;	/* Sysfs class */
>  static struct device *vme_user_bridge;		/* Pointer to bridge device */
>  
> +static struct vme_bridge *vme_user_bus;		/* Pointer to bridge */
> +
>  
>  static const int type[VME_DEVS] = {	MASTER_MINOR,	MASTER_MINOR,
>  					MASTER_MINOR,	MASTER_MINOR,
> @@ -824,10 +826,25 @@ static int __devinit vme_user_probe(struct device *dev, int cur_bus,
>  		}
>  	}
>  
> +	/*
> +	 * Increment reference count of bridge module. We don't want things
> +	 * to fall over in case the bridge module is removed while the vme_user
> +	 * driver is still loaded.
> +	 */
> +	vme_user_bus = vme_bridge_get(cur_bus);
> +	if (!vme_user_bus) {
> +		printk(KERN_ERR "%s: vme_bridge_get failed\n", driver_name);
> +		err = -EINVAL;
> +		goto err_bridge_get;
> +	}
> +

Can we not do this inside vme_master_request, vme_slave_request, etc?

I.e. Add reference count when resources are given out.

>  	return 0;
>  
>  	/* Ensure counter set correcty to destroy all sysfs devices */
>  	i = VME_DEVS;
> +err_bridge_get:
> +	for (i = 0; i < VME_DEVS; i++)
> +		device_destroy(vme_user_sysfs_class, MKDEV(VME_MAJOR, i));
>  err_sysfs:
>  	while (i > 0) {
>  		i--;
> @@ -892,6 +909,9 @@ static int __devexit vme_user_remove(struct device *dev, int cur_bus,
>  	/* Unregiser the major and minor device numbers */
>  	unregister_chrdev_region(MKDEV(VME_MAJOR, 0), VME_DEVS);
>  
> +	/* decrement bridge module reference */
> +	vme_bridge_put(vme_user_bus);
> +

This would then be done in the vme_*_free routines.

Martyn

>  	return 0;
>  }
>  
> diff --git a/drivers/staging/vme/vme.c b/drivers/staging/vme/vme.c
> index 11e28ca..759ec2b 100644
> --- a/drivers/staging/vme/vme.c
> +++ b/drivers/staging/vme/vme.c
> @@ -52,6 +52,54 @@ static struct vme_bridge *dev_to_bridge(struct device *dev)
>  }
>  
>  /*
> + * Increments the reference count of a VME bridge.
> + *
> + * If found, a pointer to the bridge is returned and the reference count
> + * of the module that owns it is incremented.
> + *
> + * On success, it can be assumed that the bridge won't be removed until
> + * the corresponding call to vme_put_bridge().
> + *
> + * Normally drivers should call vme_get_bridge() on a successfull .probe,
> + * and vme_put_bridge() when releasing the device, e.g. in .remove.
> + */
> +struct vme_bridge *vme_bridge_get(unsigned int bus_id)
> +{
> +	struct vme_bridge *bridge;
> +	struct vme_bridge *retp = NULL;
> +
> +	mutex_lock(&vme_buses_lock);
> +	list_for_each_entry(bridge, &vme_bus_list, bus_list) {
> +		if (bridge->num == bus_id) {
> +			if (!bridge->owner)
> +				dev_warn(bridge->parent,
> +					"bridge->owner not set\n");
> +			else if (try_module_get(bridge->owner))
> +				retp = bridge;
> +			break;
> +		}
> +	}
> +	mutex_unlock(&vme_buses_lock);
> +	return retp;
> +}
> +EXPORT_SYMBOL(vme_bridge_get);
> +
> +/*
> + * Decrements the reference count of a bridge
> + *
> + * This function decrements the reference count of the module that controls
> + * the bridge. It must come after a call to vme_get_bridge().
> + */
> +void vme_bridge_put(struct vme_bridge *bridge)
> +{
> +	if (!bridge->owner)
> +		dev_warn(bridge->parent, "bridge->owner not set\n");
> +	else
> +		module_put(bridge->owner);
> +}
> +EXPORT_SYMBOL(vme_bridge_put);
> +
> +/*
>   * Find the bridge that the resource is associated with.
>   */
>  static struct vme_bridge *find_bridge(struct vme_resource *resource)
> diff --git a/drivers/staging/vme/vme.h b/drivers/staging/vme/vme.h
> index 3ccb497..8fb35e2 100644
> --- a/drivers/staging/vme/vme.h
> +++ b/drivers/staging/vme/vme.h
> @@ -167,6 +167,8 @@ int vme_slot_get(struct device *);
>  int vme_register_driver(struct vme_driver *);
>  void vme_unregister_driver(struct vme_driver *);
>  
> +struct vme_bridge *vme_bridge_get(unsigned int bus_id);
> +void vme_bridge_put(struct vme_bridge *bridge);
>  
>  #endif /* _VME_H_ */
>  
> diff --git a/drivers/staging/vme/vme_bridge.h b/drivers/staging/vme/vme_bridge.h
> index 8959670..ef751a4 100644
> --- a/drivers/staging/vme/vme_bridge.h
> +++ b/drivers/staging/vme/vme_bridge.h
> @@ -113,6 +113,7 @@ struct vme_bridge {
>  	struct device *parent;	/* Parent device (eg. pdev->dev for PCI) */
>  	void *driver_priv;	/* Private pointer for the bridge driver */
>  	struct list_head bus_list; /* list of VME buses */
> +	struct module *owner;	/* module that owns the bridge */
>  
>  	struct device dev[VME_SLOTS_MAX];	/* Device registered with
>  						 * device model on VME bus


-- 
Martyn Welch (Principal Software Engineer) | Registered in England and
GE Intelligent Platforms                   | Wales (3828642) at 100
T +44(0)127322748                          | Barbirolli Square, Manchester,
E martyn.welch@xxxxxx                      | M2 3AB  VAT:GB 927559189
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