[Intel-gfx] [PATCH v9 32/70] drm/i915: Prepare for obj->mm.lock removal, v2.

[Matthew Auld]

On Tue, 23 Mar 2021 at 15:52, Maarten Lankhorst
<maarten.lankhorst at linux.intel.com> wrote:
>
> From: Thomas Hellström <thomas.hellstrom at intel.com>
>
> Stolen objects need to lock, and we may call put_pages when
> refcount drops to 0, ensure all calls are handled correctly.
>
> Changes since v1:
> - Rebase on top of upstream changes.
>
> Idea-from: Thomas Hellström <thomas.hellstrom at intel.com>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_object.h | 14 ++++++++++++++
>  drivers/gpu/drm/i915/gem/i915_gem_pages.c  | 14 ++++++++++++--
>  drivers/gpu/drm/i915/gem/i915_gem_stolen.c | 12 +++++++-----
>  3 files changed, 33 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index 983f2d4b2a85..74de195b57de 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -144,6 +144,20 @@ i915_gem_object_put(struct drm_i915_gem_object *obj)
>
>  #define assert_object_held(obj) dma_resv_assert_held((obj)->base.resv)
>
> +/*
> + * If more than one potential simultaneous locker, assert held.
> + */
> +static inline void assert_object_held_shared(struct drm_i915_gem_object *obj)
> +{
> +       /*
> +        * Note mm list lookup is protected by

What is meant with mm list here? Maybe just a stale comment?

> +        * kref_get_unless_zero().
> +        */
> +       if (IS_ENABLED(CONFIG_LOCKDEP) &&
> +           kref_read(&obj->base.refcount) > 0)
> +               lockdep_assert_held(&obj->mm.lock);
> +}
> +
>  static inline int __i915_gem_object_lock(struct drm_i915_gem_object *obj,
>                                          struct i915_gem_ww_ctx *ww,
>                                          bool intr)
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> index a24617af3c93..2d0065fa6e80 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -19,7 +19,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
>         bool shrinkable;
>         int i;
>
> -       lockdep_assert_held(&obj->mm.lock);
> +       assert_object_held_shared(obj);
>
>         if (i915_gem_object_is_volatile(obj))
>                 obj->mm.madv = I915_MADV_DONTNEED;
> @@ -70,6 +70,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
>                 struct list_head *list;
>                 unsigned long flags;
>
> +               lockdep_assert_held(&obj->mm.lock);
>                 spin_lock_irqsave(&i915->mm.obj_lock, flags);
>
>                 i915->mm.shrink_count++;
> @@ -91,6 +92,8 @@ int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
>         struct drm_i915_private *i915 = to_i915(obj->base.dev);
>         int err;
>
> +       assert_object_held_shared(obj);
> +
>         if (unlikely(obj->mm.madv != I915_MADV_WILLNEED)) {
>                 drm_dbg(&i915->drm,
>                         "Attempting to obtain a purgeable object\n");
> @@ -118,6 +121,8 @@ int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
>         if (err)
>                 return err;
>
> +       assert_object_held_shared(obj);
> +
>         if (unlikely(!i915_gem_object_has_pages(obj))) {
>                 GEM_BUG_ON(i915_gem_object_has_pinned_pages(obj));
>
> @@ -145,7 +150,7 @@ void i915_gem_object_truncate(struct drm_i915_gem_object *obj)
>  /* Try to discard unwanted pages */
>  void i915_gem_object_writeback(struct drm_i915_gem_object *obj)
>  {
> -       lockdep_assert_held(&obj->mm.lock);
> +       assert_object_held_shared(obj);
>         GEM_BUG_ON(i915_gem_object_has_pages(obj));
>
>         if (obj->ops->writeback)
> @@ -176,6 +181,8 @@ __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj)
>  {
>         struct sg_table *pages;
>
> +       assert_object_held_shared(obj);
> +
>         pages = fetch_and_zero(&obj->mm.pages);
>         if (IS_ERR_OR_NULL(pages))
>                 return pages;
> @@ -203,6 +210,9 @@ int __i915_gem_object_put_pages_locked(struct drm_i915_gem_object *obj)
>         if (i915_gem_object_has_pinned_pages(obj))
>                 return -EBUSY;
>
> +       /* May be called by shrinker from within get_pages() (on another bo) */
> +       assert_object_held_shared(obj);
> +
>         i915_gem_object_release_mmap_offset(obj);
>
>         /*
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> index 7cdb32d881d9..b0597de206de 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> @@ -637,13 +637,15 @@ static int __i915_gem_object_create_stolen(struct intel_memory_region *mem,
>         cache_level = HAS_LLC(mem->i915) ? I915_CACHE_LLC : I915_CACHE_NONE;
>         i915_gem_object_set_cache_coherency(obj, cache_level);
>
> -       err = i915_gem_object_pin_pages(obj);
> -       if (err)
> -               return err;
> +       if (WARN_ON(!i915_gem_object_trylock(obj)))
> +               return -EBUSY;
>
> -       i915_gem_object_init_memory_region(obj, mem);
> +       err = i915_gem_object_pin_pages(obj);
> +       if (!err)
> +               i915_gem_object_init_memory_region(obj, mem);

Probably more consistent to call init_memory_region() before calling
pin_pages(), but I guess it was already like that, plus it doesn't
seem to matter for stolen memory.

Reviewed-by: Matthew Auld <matthew.auld at intel.com>