Re: [PATCH 7/7] drm/i915: GEM operations need to be done under the big lock

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On 11/01/16 15:04, Chris Wilson wrote:
On Mon, Jan 11, 2016 at 03:00:20PM +0000, Chris Wilson wrote:
On Mon, Jan 11, 2016 at 02:47:17PM +0000, Tvrtko Ursulin wrote:

On 11/01/16 14:38, Chris Wilson wrote:
On Mon, Jan 11, 2016 at 02:08:41PM +0000, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

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.

intel_pm.c valleyview_setup_pctx?

Already holds it traced by the WARN_ON at its top.

Which is a nice little mutex inversion of its own. :|
i.e. rpm vs struct_mutex bug

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index b1fb43fcfeea..c8f684f8799c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -16018,9 +16018,7 @@ void intel_modeset_gem_init(struct drm_device *dev)
         struct drm_crtc *c;
         struct drm_i915_gem_object *obj;

-       mutex_lock(&dev->struct_mutex);
         intel_init_gt_powersave(dev);
-       mutex_unlock(&dev->struct_mutex);

         intel_modeset_init_hw(dev);

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index a082b4577599..90e5bf7a2402 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5224,8 +5224,6 @@ static void cherryview_setup_pctx(struct drm_device *dev)
         u32 pcbr;
         int pctx_size = 32*1024;

-       WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-
         pcbr = I915_READ(VLV_PCBR);
         if ((pcbr >> VLV_PCBR_ADDR_SHIFT) == 0) {
                 DRM_DEBUG_DRIVER("BIOS didn't set up PCBR, fixing up\n");
@@ -5247,8 +5245,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
         u32 pcbr;
         int pctx_size = 24*1024;

-       WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-
+       mutex_lock(&dev->struct_mutex);
         pcbr = I915_READ(VLV_PCBR);
         if (pcbr) {
                 /* BIOS set it up already, grab the pre-alloc'd space */
@@ -5275,7 +5272,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
         pctx = i915_gem_object_create_stolen(dev, pctx_size);
         if (!pctx) {
                 DRM_DEBUG("not enough stolen space for PCTX, disabling\n");
-               return;
+               goto out;
         }

         pctx_paddr = dev_priv->mm.stolen_base + pctx->stolen->start;
@@ -5284,6 +5281,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
  out:
         DRM_DEBUG_DRIVER("PCBR: 0x%08x\n", I915_READ(VLV_PCBR));
         dev_priv->vlv_pctx = pctx;
+       mutex_unlock(&dev->struct_mutex);
  }

  static void valleyview_cleanup_pctx(struct drm_device *dev)

Don't know, I leave this one to whoever grabbed the lock around intel_init_gt_powersave in the first place. Maybe there was a special reason.. after git blame od intel_display.c eventually completed, adding Imre and Ville to cc.

Regards,

Tvrtko
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