Re: [PATCH v2 1/6] drivers/base/devres: Introduce devm_release_action()

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

On Tue, May 07, 2019 at 04:56:05PM -0700, Dan Williams wrote:
> The devm_add_action() facility allows a resource allocation routine to
> add custom devm semantics. One such user is devm_memremap_pages().
> 
> There is now a need to manually trigger devm_memremap_pages_release().
> Introduce devm_release_action() so the release action can be triggered
> via a new devm_memunmap_pages() api in a follow-on change.
> 
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
>  drivers/base/devres.c  |   24 +++++++++++++++++++++++-
>  include/linux/device.h |    1 +
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> index e038e2b3b7ea..0bbb328bd17f 100644
> --- a/drivers/base/devres.c
> +++ b/drivers/base/devres.c
> @@ -755,10 +755,32 @@ void devm_remove_action(struct device *dev, void (*action)(void *), void *data)
>  
>  	WARN_ON(devres_destroy(dev, devm_action_release, devm_action_match,
>  			       &devres));
> -
>  }
>  EXPORT_SYMBOL_GPL(devm_remove_action);
>  
> +/**
> + * devm_release_action() - release previously added custom action
> + * @dev: Device that owns the action
> + * @action: Function implementing the action
> + * @data: Pointer to data passed to @action implementation
> + *
> + * Releases and removes instance of @action previously added by
> + * devm_add_action().  Both action and data should match one of the
> + * existing entries.
> + */
> +void devm_release_action(struct device *dev, void (*action)(void *), void *data)
> +{
> +	struct action_devres devres = {
> +		.data = data,
> +		.action = action,
> +	};
> +
> +	WARN_ON(devres_release(dev, devm_action_release, devm_action_match,
> +			       &devres));

What does WARN_ON help here?  are we going to start getting syzbot
reports of this happening?

How can this fail?

thanks,

greg k-h