Re: [PATCH 1/6] drm: pre allocate node for create_block

On Thu, Jul 04, 2013 at 11:19:58AM +0200, David Herrmann wrote:

Hi

On Wed, Jul 3, 2013 at 11:45 PM, Ben Widawsky ben@bwidawsk.net wrote:

...

For an upcoming patch where we introduce the i915 VMA, it's ideal to have the drm_mm_node as part of the VMA struct (ie. it's pre-allocated). Part of the conversion to VMAs is to kill off obj->gtt_space. Doing this will break a bunch of code, but amongst them are 2 callers of drm_mm_create_block(), both related to stolen memory.

It also allows us to embed the drm_mm_node into the object currently which provides a nice transition over to the new code.

v2: Reordered to do before ripping out obj->gtt_offset. Some minor cleanups made available because of reordering.

CC: dri-devel@lists.freedesktop.org Signed-off-by: Ben Widawsky ben@bwidawsk.net

---

drivers/gpu/drm/drm_mm.c | 16 +++++---------- drivers/gpu/drm/i915/i915_gem_gtt.c | 18 +++++++++++++---- drivers/gpu/drm/i915/i915_gem_stolen.c | 36 +++++++++++++++++++++++----------- include/drm/drm_mm.h | 9 +++++---- 4 files changed, 49 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c index 07cf99c..9e8dfbc 100644 --- a/drivers/gpu/drm/drm_mm.c +++ b/drivers/gpu/drm/drm_mm.c @@ -147,12 +147,10 @@ static void drm_mm_insert_helper(struct drm_mm_node *hole_node, } }

-struct drm_mm_node *drm_mm_create_block(struct drm_mm *mm,

•                                   unsigned long start,
  

•                                   unsigned long size,
  

•                                   bool atomic)
  

+int drm_mm_create_block(struct drm_mm *mm, struct drm_mm_node *node,

•                   unsigned long start, unsigned long size)
  

{

•   struct drm_mm_node *hole, *node;
  

•   struct drm_mm_node *hole;
    unsigned long end = start + size;
    unsigned long hole_start;
    unsigned long hole_end;
  

@@ -161,10 +159,6 @@ struct drm_mm_node *drm_mm_create_block(struct drm_mm *mm, if (hole_start > start || hole_end < end) continue;

•           node = drm_mm_kmalloc(mm, atomic);
  

•           if (unlikely(node == NULL))
  

•                   return NULL;
  

•           node->start = start;
            node->size = size;
            node->mm = mm;
  

@@ -184,11 +178,11 @@ struct drm_mm_node *drm_mm_create_block(struct drm_mm *mm, node->hole_follows = 1; }

•           return node;
  

•           return 0;
    }
  
    WARN(1, "no hole found for block 0x%lx + 0x%lx\n", start, size);
  

•   return NULL;
  

•   return -ENOSPC;
  

} EXPORT_SYMBOL(drm_mm_create_block);

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c index 66929ea..5c6fc0e 100644 --- a/drivers/gpu/drm/i915/i915_gem_gtt.c +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c @@ -629,14 +629,24 @@ void i915_gem_setup_global_gtt(struct drm_device *dev,

    /* Mark any preallocated objects as occupied */
    list_for_each_entry(obj, &dev_priv->mm.bound_list, global_list) {

•           int ret;
            DRM_DEBUG_KMS("reserving preallocated space: %x + %zx\n",
                          obj->gtt_offset, obj->base.size);
  
            BUG_ON(obj->gtt_space != I915_GTT_RESERVED);
  

•           obj->gtt_space = drm_mm_create_block(&dev_priv->mm.gtt_space,
  

•                                                obj->gtt_offset,
  

•                                                obj->base.size,
  

•                                                false);
  

•           obj->gtt_space = kzalloc(sizeof(*obj->gtt_space), GFP_KERNEL);
  

•           if (!obj->gtt_space) {
  

•                   DRM_ERROR("Failed to preserve all objects\n");
  

•                   break;
  

•           }
  

•           ret = drm_mm_create_block(&dev_priv->mm.gtt_space,
  

•                                     obj->gtt_space,
  

•                                     obj->gtt_offset,
  

•                                     obj->base.size);
  

•           if (ret) {
  

•                   DRM_DEBUG_KMS("Reservation failed\n");
  

•                   kfree(obj->gtt_space);
  

Are you sure you don't need: obj->gtt_space = NULL; here? I am no expert in i915 gem handling, but looking at i915_gem.c I think you might run into bugs if not.

I'm too lazy to actually check, but I believe you're probably right. It's fixed in a later patch where I added the getters and use node_allocated so I don't check obj->gtt_space != NULL anymore; but it would potentially be a painful bisect point.

Thanks for catching it (and the following ones).

Also, why did you add the "break;" above, but not here? I am confused.

The thought at the time was if kzalloc fails at this point, subsequent kzallocs are really likely to fail also. drm_mm_create_block OTOH is something I won't pretend to inquire about failure recurrence. I agree it looks funny though, so I'll change the break to continue.

...

•           }
            obj->has_global_gtt_mapping = 1;
    }
  
  

diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c index 8e02344..f9db84a 100644 --- a/drivers/gpu/drm/i915/i915_gem_stolen.c +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c @@ -330,6 +330,7 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev, struct drm_i915_private *dev_priv = dev->dev_private; struct drm_i915_gem_object *obj; struct drm_mm_node *stolen;

•   int ret;
  
    if (dev_priv->mm.stolen_base == 0)
            return NULL;
  

@@ -344,11 +345,15 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev, if (WARN_ON(size == 0)) return NULL;

•   stolen = drm_mm_create_block(&dev_priv->mm.stolen,
  

•                                stolen_offset, size,
  

•                                false);
  

•   if (stolen == NULL) {
  

•   stolen = kzalloc(sizeof(*stolen), GFP_KERNEL);
  

•   if (!stolen)
  

•           return NULL;
  

•   ret = drm_mm_create_block(&dev_priv->mm.stolen, stolen, stolen_offset,
  

•                             size);
  

•   if (ret) {
            DRM_DEBUG_KMS("failed to allocate stolen space\n");
  

•           kfree(stolen);
            return NULL;
    }
  
  

@@ -369,13 +374,18 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev, * later. */ if (drm_mm_initialized(&dev_priv->mm.gtt_space)) {

•           obj->gtt_space = drm_mm_create_block(&dev_priv->mm.gtt_space,
  

•                                                gtt_offset, size,
  

•                                                false);
  

•           if (obj->gtt_space == NULL) {
  

•           obj->gtt_space = kzalloc(sizeof(*obj->gtt_space), GFP_KERNEL);
  

•           if (!obj->gtt_space) {
  

•                   DRM_DEBUG_KMS("-ENOMEM stolen GTT space\n");
  

•                   goto unref_out;
  

•           }
  

•           ret = drm_mm_create_block(&dev_priv->mm.gtt_space,
  

•                                     obj->gtt_space,
  

•                                     gtt_offset, size);
  

•           if (ret) {
                    DRM_DEBUG_KMS("failed to allocate stolen GTT space\n");
  

•                   drm_gem_object_unreference(&obj->base);
  

•                   return NULL;
  

•                   goto unref_out;
  

Again: kfree(obj->gtt_space); obj->gtt_space = NULL; Otherwise, if gem-cleanup calls drm_mm_put_block() on an already removed node, you end up with NULL-derefs in drm_mm.c

...

            }
    } else
            obj->gtt_space = I915_GTT_RESERVED;

@@ -385,8 +395,12 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,

    list_add_tail(&obj->global_list, &dev_priv->mm.bound_list);
    list_add_tail(&obj->mm_list, &dev_priv->mm.inactive_list);

•   return obj;
  

+unref_out:

•   drm_gem_object_unreference(&obj->base);
  

•   drm_mm_put_block(stolen);
  

"stolen" is already cleared by drm_gem_object_unreference(). So that's a double-free here.

The drm_mm_create_block() change looks good. Cheers David

Thanks for reviewing the i915 parts so thoroughly :D

...

•   return NULL;
  

}

void diff --git a/include/drm/drm_mm.h b/include/drm/drm_mm.h index 88591ef..d8b56b7 100644 --- a/include/drm/drm_mm.h +++ b/include/drm/drm_mm.h @@ -138,10 +138,10 @@ static inline unsigned long drm_mm_hole_node_end(struct drm_mm_node *hole_node) /*

• Basic range manager support (drm_mm.c)

*/ -extern struct drm_mm_node *drm_mm_create_block(struct drm_mm *mm,

•                                          unsigned long start,
  

•                                          unsigned long size,
  

•                                          bool atomic);
  

+extern int drm_mm_create_block(struct drm_mm *mm,

•                          struct drm_mm_node *node,
  

•                          unsigned long start,
  

•                          unsigned long size);
  

extern struct drm_mm_node *drm_mm_get_block_generic(struct drm_mm_node *node, unsigned long size, unsigned alignment, @@ -155,6 +155,7 @@ extern struct drm_mm_node *drm_mm_get_block_range_generic( unsigned long start, unsigned long end, int atomic);

static inline struct drm_mm_node *drm_mm_get_block(struct drm_mm_node *parent, unsigned long size, unsigned alignment) -- 1.8.3.2

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