linux-kernel - Re: [PATCH 09/22] memremap: lift the devmap_enable manipulation into devm_memremap

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Date:   Thu, 13 Jun 2019 19:34:31 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Christoph Hellwig <hch@....de>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/22] memremap: lift the devmap_enable manipulation into
 devm_memremap_pages

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@....de>

Jason