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

[Ben Widawsky <ben@bwidawsk.net>]

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
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ben Widawsky, Intel Open Source Technology Center