[Intel-gfx] [PATCH 1/3] drm/i915: Only update the current userptr worker

[Michał Winiarski]

On Tue, Jun 30, 2015 at 05:55:31PM +0100, Chris Wilson wrote:
> The userptr worker allows for a slight race condition where upon there
> may two or more threads calling get_user_pages for the same object. When
> we have the array of pages, then we serialise the update of the object.
> However, the worker should only overwrite the obj->userptr.work pointer
> if and only if it is the active one. Currently we clear it for a
> secondary worker with the effect that we may rarely force a second
> lookup.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Whole series:
Tested-by: Michał Winiarski <michal.winiarski at intel.com>

> ---
>  drivers/gpu/drm/i915/i915_gem_userptr.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index 7a5242cd5ea5..cb367d9f7909 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -581,17 +581,17 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
>  	}
>  
>  	mutex_lock(&dev->struct_mutex);
> -	if (obj->userptr.work != &work->work) {
> -		ret = 0;
> -	} else if (pinned == num_pages) {
> -		ret = st_set_pages(&obj->pages, pvec, num_pages);
> -		if (ret == 0) {
> -			list_add_tail(&obj->global_list, &to_i915(dev)->mm.unbound_list);
> -			pinned = 0;
> +	if (obj->userptr.work == &work->work) {
> +		if (pinned == num_pages) {
> +			ret = st_set_pages(&obj->pages, pvec, num_pages);
> +			if (ret == 0) {
> +				list_add_tail(&obj->global_list, &to_i915(dev)->mm.unbound_list);
> +				pinned = 0;
> +			}
>  		}
> +		obj->userptr.work = ERR_PTR(ret);
>  	}
>  
> -	obj->userptr.work = ERR_PTR(ret);
>  	obj->userptr.workers--;
>  	drm_gem_object_unreference(&obj->base);
>  	mutex_unlock(&dev->struct_mutex);
> -- 
> 2.1.4
> 
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