Re: [PATCH] drm/i915/userptr: Replace get_user_pages()

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 17/03/16 09:37, Chris Wilson wrote:
> Although the long term future of get_user_pages_locked() itself is
> doubtful, the kernel currently recommends:
>
> /* get_user_pages should be phased out in favor of
>   * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
>   * should use get_user_pages because it cannot pass
>   * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
>   */
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem_userptr.c | 14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index 54088a4d6498..fa7d8a8b66ef 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -500,20 +500,22 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
>   		pvec = drm_malloc_ab(npages, sizeof(struct page *));
>   	if (pvec != NULL) {
>   		struct mm_struct *mm = obj->userptr.mm->mm;
> +		int locked = 1;
>
>   		down_read(&mm->mmap_sem);
>   		while (pinned < npages) {
> -			ret = get_user_pages(work->task, mm,
> -					     obj->userptr.ptr + pinned * PAGE_SIZE,
> -					     npages - pinned,
> -					     !obj->userptr.read_only, 0,
> -					     pvec + pinned, NULL);
> +			ret = get_user_pages_locked(work->task, mm,
> +						    obj->userptr.ptr + pinned * PAGE_SIZE,
> +						    npages - pinned,
> +						    !obj->userptr.read_only, 0,
> +						    pvec + pinned, &locked);
>   			if (ret < 0)
>   				break;
>
>   			pinned += ret;
>   		}
> -		up_read(&mm->mmap_sem);
> +		if (locked)
> +			up_read(&mm->mmap_sem);
>   	}
>
>   	mutex_lock(&dev->struct_mutex);
>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Is it just cleanup or actually improves some real (as in hit by someone) 
scenario?

Regards,

Tvrtko
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