Re: [PATCH 07/13] drm/i915: Introduce dedicated object VMA iterator

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Jan 08, 2016 at 01:29:14PM +0000, Tvrtko Ursulin wrote:
> 
> On 08/01/16 11:29, Tvrtko Ursulin wrote:
> >From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >
> >Purpose is to catch places which iterate the object VMA list
> >without holding the big lock.
> >
> >Implemented by open coding list_for_each_entry to make the
> >macro compatible with existing call sites.
> >
> >Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> >---
> >  drivers/gpu/drm/i915/i915_debugfs.c      |  8 ++++----
> >  drivers/gpu/drm/i915/i915_drv.h          |  6 ++++++
> >  drivers/gpu/drm/i915/i915_gem.c          | 24 ++++++++++++------------
> >  drivers/gpu/drm/i915/i915_gem_gtt.c      |  2 +-
> >  drivers/gpu/drm/i915/i915_gem_shrinker.c |  2 +-
> >  drivers/gpu/drm/i915/i915_gpu_error.c    |  4 ++--
> >  6 files changed, 26 insertions(+), 20 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> >index 714a45cf8a51..d7c2a3201161 100644
> >--- a/drivers/gpu/drm/i915/i915_debugfs.c
> >+++ b/drivers/gpu/drm/i915/i915_debugfs.c
> >@@ -117,7 +117,7 @@ static u64 i915_gem_obj_total_ggtt_size(struct drm_i915_gem_object *obj)
> >  	u64 size = 0;
> >  	struct i915_vma *vma;
> >
> >-	list_for_each_entry(vma, &obj->vma_list, vma_link) {
> >+	i915_gem_obj_for_each_vma(vma, obj) {
> >  		if (i915_is_ggtt(vma->vm) &&
> >  		    drm_mm_node_allocated(&vma->node))
> >  			size += vma->node.size;
> >@@ -155,7 +155,7 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
> >  		   obj->madv == I915_MADV_DONTNEED ? " purgeable" : "");
> >  	if (obj->base.name)
> >  		seq_printf(m, " (name: %d)", obj->base.name);
> >-	list_for_each_entry(vma, &obj->vma_list, vma_link) {
> >+	i915_gem_obj_for_each_vma(vma, obj) {
> >  		if (vma->pin_count > 0)
> >  			pin_count++;
> >  	}
> >@@ -164,7 +164,7 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
> >  		seq_printf(m, " (display)");
> >  	if (obj->fence_reg != I915_FENCE_REG_NONE)
> >  		seq_printf(m, " (fence: %d)", obj->fence_reg);
> >-	list_for_each_entry(vma, &obj->vma_list, vma_link) {
> >+	i915_gem_obj_for_each_vma(vma, obj) {
> >  		seq_printf(m, " (%sgtt offset: %08llx, size: %08llx",
> >  			   i915_is_ggtt(vma->vm) ? "g" : "pp",
> >  			   vma->node.start, vma->node.size);
> >@@ -342,7 +342,7 @@ static int per_file_stats(int id, void *ptr, void *data)
> >  		stats->shared += obj->base.size;
> >
> >  	if (USES_FULL_PPGTT(obj->base.dev)) {
> >-		list_for_each_entry(vma, &obj->vma_list, vma_link) {
> >+		i915_gem_obj_for_each_vma(vma, obj) {
> >  			struct i915_hw_ppgtt *ppgtt;
> >
> >  			if (!drm_mm_node_allocated(&vma->node))
> >diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> >index b77a5d84eac2..0406a020dfcc 100644
> >--- a/drivers/gpu/drm/i915/i915_drv.h
> >+++ b/drivers/gpu/drm/i915/i915_drv.h
> >@@ -2852,6 +2852,12 @@ struct drm_i915_gem_object *i915_gem_object_create_from_data(
> >  void i915_gem_free_object(struct drm_gem_object *obj);
> >  void i915_gem_vma_destroy(struct i915_vma *vma);
> >
> >+#define i915_gem_obj_for_each_vma(vma, obj) \
> >+	for (WARN_ON_ONCE(!mutex_is_locked(&(obj)->base.dev->struct_mutex)), \
> >+	     vma = list_first_entry(&(obj)->vma_list, typeof(*vma), vma_link);\
> >+	     &vma->vma_link != (&(obj)->vma_list); \
> >+	     vma = list_next_entry(vma, vma_link))
> >+
> 
> 
> Unfortunately error capture is not happy with this approach. Can't even see
> that error capture attempts to grab the mutex anywhere.
> 
> So what? Drop the idea or add a "doing error capture" flag somewhere?

Fix the bugs. Not surprise at all that we've screwed this up all over the
place ;-) Afaics modeset code isn't much better either ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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