linux-kernel - Re: [PATCH 1/4] mm: introduce vma_set

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Date:   Thu, 8 Oct 2020 14:49:03 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christian König <ckoenig.leichtzumerken@...il.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linaro-mm-sig@...ts.linaro.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-media@...r.kernel.org>,
        <chris@...is-wilson.co.uk>, <airlied@...hat.com>,
        <akpm@...ux-foundation.org>, <daniel@...ll.ch>,
        <sumit.semwal@...aro.org>
Subject: Re: [PATCH 1/4] mm: introduce vma_set_file function v2

On 10/8/20 4:23 AM, Christian König wrote:
> Add the new vma_set_file() function to allow changing
> vma->vm_file with the necessary refcount dance.
> 
> v2: add more users of this.
> 
> Signed-off-by: Christian König <christian.koenig@....com>
> ---
>   drivers/dma-buf/dma-buf.c                  | 16 +++++-----------
>   drivers/gpu/drm/etnaviv/etnaviv_gem.c      |  4 +---
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c |  3 +--
>   drivers/gpu/drm/i915/gem/i915_gem_mman.c   |  4 ++--
>   drivers/gpu/drm/msm/msm_gem.c              |  4 +---
>   drivers/gpu/drm/omapdrm/omap_gem.c         |  3 +--
>   drivers/gpu/drm/vgem/vgem_drv.c            |  3 +--
>   drivers/staging/android/ashmem.c           |  5 ++---
>   include/linux/mm.h                         |  2 ++
>   mm/mmap.c                                  | 16 ++++++++++++++++
>   10 files changed, 32 insertions(+), 28 deletions(-)

Looks like a nice cleanup. Two comments below.

...

> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> index 3d69e51f3e4d..c9d5f1a38af3 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> @@ -893,8 +893,8 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct *vma)
>   	 * requires avoiding extraneous references to their filp, hence why
>   	 * we prefer to use an anonymous file for their mmaps.
>   	 */
> -	fput(vma->vm_file);
> -	vma->vm_file = anon;
> +	vma_set_file(vma, anon);
> +	fput(anon);

That's one fput() too many, isn't it?

...

> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> index 10b4be1f3e78..a51dc089896e 100644
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -450,9 +450,8 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
>   		vma_set_anonymous(vma);
>   	}
>   
> -	if (vma->vm_file)
> -		fput(vma->vm_file);
> -	vma->vm_file = asma->file;
> +	vma_set_file(vma, asma->file);
> +	fput(asma->file);

Same here: that fput() seems wrong, as it was already done within vma_set_file().


thanks,
-- 
John Hubbard
NVIDIA