linux-kernel - Re: [PATCH v2 3/3] infiniband/mm: convert to the new put_user

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Message-ID: <20181005152055.GB20776@ziepe.ca>
Date:   Fri, 5 Oct 2018 09:20:55 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     john.hubbard@...il.com
Cc:     Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Doug Ledford <dledford@...hat.com>,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Christian Benvenuti <benve@...co.com>
Subject: Re: [PATCH v2 3/3] infiniband/mm: convert to the new
 put_user_page[s]() calls

On Thu, Oct 04, 2018 at 09:02:25PM -0700, john.hubbard@...il.com wrote:
> From: John Hubbard <jhubbard@...dia.com>
> 
> For code that retains pages via get_user_pages*(),
> release those pages via the new put_user_page(),
> instead of put_page().
> 
> This prepares for eventually fixing the problem described
> in [1], and is following a plan listed in [2], [3], [4].
> 
> [1] https://lwn.net/Articles/753027/ : "The Trouble with get_user_pages()"
> 
> [2] https://lkml.kernel.org/r/20180709080554.21931-1-jhubbard@nvidia.com
>     Proposed steps for fixing get_user_pages() + DMA problems.
> 
> [3]https://lkml.kernel.org/r/20180710082100.mkdwngdv5kkrcz6n@quack2.suse.cz
>     Bounce buffers (otherwise [2] is not really viable).
> 
> [4] https://lkml.kernel.org/r/20181003162115.GG24030@quack2.suse.cz
>     Follow-up discussions.
> 
> CC: Doug Ledford <dledford@...hat.com>
> CC: Jason Gunthorpe <jgg@...pe.ca>
> CC: Mike Marciniszyn <mike.marciniszyn@...el.com>
> CC: Dennis Dalessandro <dennis.dalessandro@...el.com>
> CC: Christian Benvenuti <benve@...co.com>
> 
> CC: linux-rdma@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> CC: linux-mm@...ck.org
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
>  drivers/infiniband/core/umem.c              |  2 +-
>  drivers/infiniband/core/umem_odp.c          |  2 +-
>  drivers/infiniband/hw/hfi1/user_pages.c     | 11 ++++-------
>  drivers/infiniband/hw/mthca/mthca_memfree.c |  6 +++---
>  drivers/infiniband/hw/qib/qib_user_pages.c  | 11 ++++-------
>  drivers/infiniband/hw/qib/qib_user_sdma.c   |  8 ++++----
>  drivers/infiniband/hw/usnic/usnic_uiom.c    |  2 +-
>  7 files changed, 18 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index a41792dbae1f..9430d697cb9f 100644
> +++ b/drivers/infiniband/core/umem.c
> @@ -60,7 +60,7 @@ static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int d
>  		page = sg_page(sg);
>  		if (!PageDirty(page) && umem->writable && dirty)
>  			set_page_dirty_lock(page);
> -		put_page(page);
> +		put_user_page(page);
>  	}

How about ?

if (umem->writable && dirty)
     put_user_pages_dirty_lock(&page, 1);
else
     put_user_page(page);

?

> diff --git a/drivers/infiniband/hw/hfi1/user_pages.c b/drivers/infiniband/hw/hfi1/user_pages.c
> index e341e6dcc388..99ccc0483711 100644
> +++ b/drivers/infiniband/hw/hfi1/user_pages.c
> @@ -121,13 +121,10 @@ int hfi1_acquire_user_pages(struct mm_struct *mm, unsigned long vaddr, size_t np
>  void hfi1_release_user_pages(struct mm_struct *mm, struct page **p,
>  			     size_t npages, bool dirty)
>  {
> -	size_t i;
> -
> -	for (i = 0; i < npages; i++) {
> -		if (dirty)
> -			set_page_dirty_lock(p[i]);
> -		put_page(p[i]);
> -	}
> +	if (dirty)
> +		put_user_pages_dirty_lock(p, npages);
> +	else
> +		put_user_pages(p, npages);

And I know Jan gave the feedback to remove the bool argument, but just
pointing out that quite possibly evey caller will wrapper it in an if
like this..

Jason