[Intel-gfx] [PATCH 04/23] drm/i915/gem: Only revoke mmap handlers if active

[Tvrtko Ursulin]

On 02/07/2020 09:32, Chris Wilson wrote:
> Avoid waking up the device and taking stale locks if we know that the
> object is not currently mmapped. This is particularly useful as not many
> object are actually mmapped and so we can destroy them without waking
> the device up, and gives us a little more freedom of workqueue ordering
> during shutdown.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_mman.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> index fe27c5b344e3..522ca4f51b53 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
> @@ -516,8 +516,11 @@ void i915_gem_object_release_mmap_offset(struct drm_i915_gem_object *obj)
>    */
>   void i915_gem_object_release_mmap(struct drm_i915_gem_object *obj)
>   {
> -	i915_gem_object_release_mmap_gtt(obj);
> -	i915_gem_object_release_mmap_offset(obj);
> +	if (obj->userfault_count)
> +		i915_gem_object_release_mmap_gtt(obj);
> +
> +	if (!RB_EMPTY_ROOT(&obj->mmo.offsets))
> +		i915_gem_object_release_mmap_offset(obj);
>   }
>   
>   static struct i915_mmap_offset *
> 

Both conditions will need explaining why they are not racy.

First should normally be done under the ggtt->mutex, second under 
obj->mmo.lock.

Regards,

Tvrtko