Re: [PATCH 22/27] drm/i915/overlay: Drop struct_mutex guard

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

On 25/09/2019 13:53, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2019-09-25 13:43:46)
>>
>> On 25/09/2019 11:01, Chris Wilson wrote:
>>> The overlay uses the modeset mutex to control itself and only required
>>> the struct_mutex for requests, which is now obsolete.
>>>
>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> ---
>>>    drivers/gpu/drm/i915/display/intel_display.c |  7 +------
>>>    drivers/gpu/drm/i915/display/intel_overlay.c | 13 -------------
>>>    drivers/gpu/drm/i915/gt/intel_reset.c        |  4 ----
>>>    3 files changed, 1 insertion(+), 23 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
>>> index 99ddbb7bedbc..038f14d9b5c9 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_display.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_display.c
>>> @@ -5738,13 +5738,8 @@ void hsw_disable_ips(const struct intel_crtc_state *crtc_state)
>>>    
>>>    static void intel_crtc_dpms_overlay_disable(struct intel_crtc *intel_crtc)
>>>    {
>>> -     if (intel_crtc->overlay) {
>>> -             struct drm_device *dev = intel_crtc->base.dev;
>>> -
>>> -             mutex_lock(&dev->struct_mutex);
>>> +     if (intel_crtc->overlay)
>>>                (void) intel_overlay_switch_off(intel_crtc->overlay);
>>> -             mutex_unlock(&dev->struct_mutex);
>>> -     }
>>>    
>>>        /* Let userspace switch the overlay on again. In most cases userspace
>>>         * has to recompute where to put it anyway.
>>> diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c b/drivers/gpu/drm/i915/display/intel_overlay.c
>>> index e12e1a753af0..daea112cbb87 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_overlay.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_overlay.c
>>> @@ -439,8 +439,6 @@ static int intel_overlay_release_old_vid(struct intel_overlay *overlay)
>>>        struct i915_request *rq;
>>>        u32 *cs;
>>>    
>>> -     lockdep_assert_held(&dev_priv->drm.struct_mutex);
>>> -
>>>        /*
>>>         * Only wait if there is actually an old frame to release to
>>>         * guarantee forward progress.
>>> @@ -751,7 +749,6 @@ static int intel_overlay_do_put_image(struct intel_overlay *overlay,
>>>        struct i915_vma *vma;
>>>        int ret, tmp_width;
>>>    
>>> -     lockdep_assert_held(&dev_priv->drm.struct_mutex);
>>>        WARN_ON(!drm_modeset_is_locked(&dev_priv->drm.mode_config.connection_mutex));
>>>    
>>>        ret = intel_overlay_release_old_vid(overlay);
>>> @@ -852,7 +849,6 @@ int intel_overlay_switch_off(struct intel_overlay *overlay)
>>>        struct drm_i915_private *dev_priv = overlay->i915;
>>>        int ret;
>>>    
>>> -     lockdep_assert_held(&dev_priv->drm.struct_mutex);
>>>        WARN_ON(!drm_modeset_is_locked(&dev_priv->drm.mode_config.connection_mutex));
>>>    
>>>        ret = intel_overlay_recover_from_interrupt(overlay);
>>> @@ -1068,11 +1064,7 @@ int intel_overlay_put_image_ioctl(struct drm_device *dev, void *data,
>>>    
>>>        if (!(params->flags & I915_OVERLAY_ENABLE)) {
>>>                drm_modeset_lock_all(dev);
>>> -             mutex_lock(&dev->struct_mutex);
>>> -
>>>                ret = intel_overlay_switch_off(overlay);
>>> -
>>> -             mutex_unlock(&dev->struct_mutex);
>>>                drm_modeset_unlock_all(dev);
>>>    
>>>                return ret;
>>> @@ -1088,7 +1080,6 @@ int intel_overlay_put_image_ioctl(struct drm_device *dev, void *data,
>>>                return -ENOENT;
>>>    
>>>        drm_modeset_lock_all(dev);
>>> -     mutex_lock(&dev->struct_mutex);
>>>    
>>>        if (i915_gem_object_is_tiled(new_bo)) {
>>>                DRM_DEBUG_KMS("buffer used for overlay image can not be tiled\n");
>>> @@ -1152,14 +1143,12 @@ int intel_overlay_put_image_ioctl(struct drm_device *dev, void *data,
>>>        if (ret != 0)
>>>                goto out_unlock;
>>>    
>>> -     mutex_unlock(&dev->struct_mutex);
>>>        drm_modeset_unlock_all(dev);
>>>        i915_gem_object_put(new_bo);
>>>    
>>>        return 0;
>>>    
>>>    out_unlock:
>>> -     mutex_unlock(&dev->struct_mutex);
>>>        drm_modeset_unlock_all(dev);
>>>        i915_gem_object_put(new_bo);
>>>    
>>> @@ -1233,7 +1222,6 @@ int intel_overlay_attrs_ioctl(struct drm_device *dev, void *data,
>>>        }
>>>    
>>>        drm_modeset_lock_all(dev);
>>> -     mutex_lock(&dev->struct_mutex);
>>>    
>>>        ret = -EINVAL;
>>>        if (!(attrs->flags & I915_OVERLAY_UPDATE_ATTRS)) {
>>> @@ -1290,7 +1278,6 @@ int intel_overlay_attrs_ioctl(struct drm_device *dev, void *data,
>>>    
>>>        ret = 0;
>>>    out_unlock:
>>> -     mutex_unlock(&dev->struct_mutex);
>>>        drm_modeset_unlock_all(dev);
>>>    
>>>        return ret;
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_reset.c b/drivers/gpu/drm/i915/gt/intel_reset.c
>>> index 2685c0103e90..ee0c5c24282c 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_reset.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_reset.c
>>> @@ -1265,10 +1265,6 @@ int intel_gt_terminally_wedged(struct intel_gt *gt)
>>>        if (!test_bit(I915_RESET_BACKOFF, &gt->reset.flags))
>>>                return -EIO;
>>>    
>>> -     /* XXX intel_reset_finish() still takes struct_mutex!!! */
>>> -     if (mutex_is_locked(&gt->i915->drm.struct_mutex))
>>> -             return -EAGAIN;
>>> -
>>
>> What is this hunk doing here?
> 
> Because the overlay used struct_mutex, now it does not.

Now you see why I insist on comments and even better if they are up to 
date! :) (intel_reset_finish?!)

If you are confident overlay is the only place which can interfere here 
then:

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

If not we'll find out sooner or later.

Regards,

Tvrtko
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