linux-kernel - Re: [PATCH] gpu: drm: tegra: Adding new typedef vm_fault

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Date:   Wed, 18 Apr 2018 10:24:39 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     airlied@...ux.ie, jonathanh@...dia.com,
        dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, willy@...radead.org
Subject: Re: [PATCH] gpu: drm: tegra: Adding new typedef vm_fault_t

On Tue, Apr 17, 2018 at 07:17:55PM +0530, Souptick Joarder wrote:
> Use new return type vm_fault_t for fault handler. For
> now, this is just documenting that the function returns
> a VM_FAULT value rather than an errno. Once all instances
> are converted, vm_fault_t will become a distinct type.
> 
> Reference id -> 1c8f422059ae ("mm: change return type to
> vm_fault_t")
> 
> Previously vm_insert_page() returns err which driver
> mapped into VM_FAULT_* type. The new function 
> vmf_insert_page() will replace this inefficiency by
> returning VM_FAULT_* type.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> ---
>  drivers/gpu/drm/tegra/gem.c | 18 ++----------------
>  1 file changed, 2 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 49b9bf2..6121493 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -422,14 +422,13 @@ int tegra_bo_dumb_create(struct drm_file *file, struct drm_device *drm,
>  	return 0;
>  }
> 
> -static int tegra_bo_fault(struct vm_fault *vmf)
> +static vm_fault_t tegra_bo_fault(struct vm_fault *vmf)
>  {
>  	struct vm_area_struct *vma = vmf->vma;
>  	struct drm_gem_object *gem = vma->vm_private_data;
>  	struct tegra_bo *bo = to_tegra_bo(gem);
>  	struct page *page;
>  	pgoff_t offset;
> -	int err;
> 
>  	if (!bo->pages)
>  		return VM_FAULT_SIGBUS;
> @@ -437,20 +436,7 @@ static int tegra_bo_fault(struct vm_fault *vmf)
>  	offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
>  	page = bo->pages[offset];
> 
> -	err = vm_insert_page(vma, vmf->address, page);
> -	switch (err) {
> -	case -EAGAIN:
> -	case 0:
> -	case -ERESTARTSYS:
> -	case -EINTR:
> -	case -EBUSY:
> -		return VM_FAULT_NOPAGE;
> -
> -	case -ENOMEM:
> -		return VM_FAULT_OOM;
> -	}
> -
> -	return VM_FAULT_SIGBUS;
> +	return vmf_insert_page(vma, vmf->address, page);
>  }

This new function returns VM_FAULT_NOPAGE only for 0 and -EBUSY, whereas
we used to return VM_FAULT_NOPAGE for -EAGAIN, -ERESTARTSYS and -EINTR
as well. Was this previously wrong?

Thierry

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