Re: [PATCH v4 2/5] devcoredump: Add per device sysfs entry to enable/disable coredump

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, Aug 09, 2022 at 08:35:24AM -0700, Manish Mandlik wrote:
> The /sys/class/devcoredump/disabled provides only one-way disable
> functionality. Also, disabling devcoredump using it disables the
> devcoredump functionality for everyone who is using it.
> 
> Provide a way to selectively enable/disable devcoredump for the device
> which is bound to a driver that implements the '.coredump()' callback.
> 
> This adds the 'coredump_disabled' driver attribute. When the driver
> implements the '.coredump()' callback, 'coredump_disabled' file is added
> along with the 'coredump' file in the sysfs folder of the device upon
> driver binding. The file is removed when the driver is unbound.
> 
> Drivers can use this attribute to enable/disable devcoredump and the
> userspace can write 0 or 1 to /sys/devices/.../coredump_disabled sysfs
> entry to control enabling/disabling of devcoredump for that device.
> 
> Signed-off-by: Manish Mandlik <mmandlik@google.com>
> Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
> ---
> 
> Changes in v4:
> - New patch in the series
> 
>  drivers/base/dd.c          | 43 +++++++++++++++++++++++++++++++++++---
>  drivers/base/devcoredump.c |  2 +-
>  include/linux/device.h     |  4 ++++
>  3 files changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 11b0fb6414d3..c76d1145c6d9 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -426,6 +426,31 @@ static ssize_t coredump_store(struct device *dev, struct device_attribute *attr,
>  }
>  static DEVICE_ATTR_WO(coredump);
>  
> +static ssize_t coredump_disabled_show(struct device *dev,
> +				      struct device_attribute *attr,
> +				      char *buf)
> +{
> +	return scnprintf(buf, 3, "%d\n", dev->coredump_disabled);

Also, please use sysfs_emit() for any sysfs file output.  It's in all
active kernels for a very long time now.

> +}
> +
> +static ssize_t coredump_disabled_store(struct device *dev,
> +				       struct device_attribute *attr,
> +				       const char *buf, size_t count)
> +{
> +	long coredump_disabled;
> +
> +	if (!kstrtol(buf, 10, &coredump_disabled)) {
> +		/* Consider any non-zero value as true */

We have a "Y/N/0/1/y/n" check function for sysfs store callbacks that
you should use instead.



> +		if (coredump_disabled)
> +			dev->coredump_disabled = true;
> +		else
> +			dev->coredump_disabled = false;
> +	}
> +
> +	return count;
> +}
> +static DEVICE_ATTR_RW(coredump_disabled);
> +
>  static int driver_sysfs_add(struct device *dev)
>  {
>  	int ret;
> @@ -448,9 +473,19 @@ static int driver_sysfs_add(struct device *dev)
>  		return 0;
>  
>  	ret = device_create_file(dev, &dev_attr_coredump);
> -	if (!ret)
> -		return 0;
> +	if (ret)
> +		goto rm_driver;
> +
> +	ret = device_create_file(dev, &dev_attr_coredump_disabled);

Please use an attribute group now that you have multiple files.



> +	if (ret)
> +		goto rm_coredump;
>  
> +	return 0;
> +
> +rm_coredump:
> +	device_remove_file(dev, &dev_attr_coredump);
> +
> +rm_driver:
>  	sysfs_remove_link(&dev->kobj, "driver");
>  
>  rm_dev:
> @@ -466,8 +501,10 @@ static void driver_sysfs_remove(struct device *dev)
>  	struct device_driver *drv = dev->driver;
>  
>  	if (drv) {
> -		if (drv->coredump)
> +		if (drv->coredump) {
> +			device_remove_file(dev, &dev_attr_coredump_disabled);
>  			device_remove_file(dev, &dev_attr_coredump);
> +		}
>  		sysfs_remove_link(&drv->p->kobj, kobject_name(&dev->kobj));
>  		sysfs_remove_link(&dev->kobj, "driver");
>  	}
> diff --git a/drivers/base/devcoredump.c b/drivers/base/devcoredump.c
> index f4d794d6bb85..c5e9af9f3181 100644
> --- a/drivers/base/devcoredump.c
> +++ b/drivers/base/devcoredump.c
> @@ -255,7 +255,7 @@ void dev_coredumpm(struct device *dev, struct module *owner,
>  	struct devcd_entry *devcd;
>  	struct device *existing;
>  
> -	if (devcd_disabled)
> +	if (devcd_disabled || dev->coredump_disabled)
>  		goto free;
>  
>  	existing = class_find_device(&devcd_class, NULL, dev,
> diff --git a/include/linux/device.h b/include/linux/device.h
> index dc941997795c..120dd656f99d 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -469,6 +469,8 @@ struct device_physical_location {
>   * 		This identifies the device type and carries type-specific
>   * 		information.
>   * @mutex:	Mutex to synchronize calls to its driver.
> + * @coredump_disabled: Can be used by drivers to selectively enable/disable the
> + *		coredump for a particular device via sysfs entry.
>   * @bus:	Type of bus device is on.
>   * @driver:	Which driver has allocated this
>   * @platform_data: Platform data specific to the device.
> @@ -561,6 +563,8 @@ struct device {
>  	const char		*init_name; /* initial name of the device */
>  	const struct device_type *type;
>  
> +	bool			coredump_disabled;
> +

That just hosed the alignment in this structure :(

Please be aware of how memory layouts for common kernel structures are
managed, and try not to add holes when you do not need to.

thanks,

greg k-h