[Intel-gfx] [PATCH 07/12] drm/i915: GEM operations need to be done under the big lock

[Chris Wilson]

On Tue, Feb 02, 2016 at 11:06:25AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> VMA creation and GEM list management need the big lock.
> 
> v2:
> 
> Mutex unlock ended on the wrong path somehow. (0-day, Julia Lawall)
> 
> Not to mention drm_gem_object_unreference was there in existing
> code with no mutex held.
> 
> v3:
> 
> Some callers of i915_gem_object_create_stolen_for_preallocated
> already hold the lock so move the mutex into the other caller
> as well.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_stolen.c | 3 +++
>  drivers/gpu/drm/i915/intel_display.c   | 8 ++++++--
>  2 files changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> index c384dc9c8a63..a97a5e762c0f 100644
> --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> @@ -635,6 +635,9 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
>  	if (!drm_mm_initialized(&dev_priv->mm.stolen))
>  		return NULL;
>  
> +	if (WARN_ON_ONCE(!mutex_is_locked(&dev->struct_mutex)))
> +		return NULL;

I'm not keen on !mutex_is_locked(), since it can also just be another
thread holding the struct_mutex that grants us protection from this
check. At least lockdep checks that the caller holds the lock.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre