Re: [PATCH 09/22] memremap: lift the devmap_enable manipulation into devm_memremap_pages

[Jason Gunthorpe]

On Thu, Jun 13, 2019 at 11:43:12AM +0200, Christoph Hellwig wrote:
> Just check if there is a ->page_free operation set and take care of the
> static key enable, as well as the put using device managed resources.
> diff --git a/mm/hmm.c b/mm/hmm.c
> index c76a1b5defda..6dc769feb2e1 100644
> +++ b/mm/hmm.c
> @@ -1378,8 +1378,6 @@ struct hmm_devmem *hmm_devmem_add(const struct hmm_devmem_ops *ops,
>  	void *result;
>  	int ret;
>  
> -	dev_pagemap_get_ops();
> -

Where was the matching dev_pagemap_put_ops() for this hmm case? This
is a bug fix too?

The nouveau driver is the only one to actually call this hmm function
and it does it as part of a probe function. 

Seems reasonable, however, in the unlikely event that it fails to init
'dmem' the driver will retain a dev_pagemap_get_ops until it unloads.
This imbalance doesn't seem worth worrying about.

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

Jason