[Intel-gfx] [PATCH v4 31/61] drm/i915: Prepare for obj->mm.lock removal

[Thomas Hellström]

On 10/16/20 12:44 PM, Maarten Lankhorst 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.
>
> Idea-from: Thomas Hellström <thomas.hellstrom at intel.com>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst 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 | 10 +++++++++-
>   3 files changed, 35 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index 8db84ce09d9f..a3a701d849bf 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -112,6 +112,20 @@ 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
> +	 * 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 ef1d5fabd077..429ec652c394 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> @@ -18,7 +18,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
>   	unsigned long supported = INTEL_INFO(i915)->page_sizes;
>   	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;
> @@ -67,6 +67,7 @@ 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++;
> @@ -88,6 +89,8 @@ 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");
> @@ -115,6 +118,8 @@ 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));
>   
> @@ -142,7 +147,7 @@ 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)
> @@ -175,6 +180,8 @@ __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;
> @@ -202,6 +209,9 @@ 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 9a9242b5a99f..1fd287ce86f4 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_stolen.c
> @@ -593,11 +593,19 @@ __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);
>   
> +	if (WARN_ON(!i915_gem_object_trylock(obj))) {
> +		err = -EBUSY;
> +		goto cleanup;
> +	}

We should probably keep the _isolated annotation here. I think it needs 
to be used elsewhere anyway.

Otherwise

Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>