Re: [PATCH 1/7] drm/i915: Introduce i915_address_space.mutex

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jul 11, 2018 at 08:36:02AM +0100, Chris Wilson wrote:
> Add a mutex into struct i915_address_space to be used while operating on
> the vma and their lists for a particular vm. As this may be called from
> the shrinker, we taint the mutex with fs_reclaim so that from the start
> lockdep warns us if we are caught holding the mutex across an
> allocation. (With such small steps we will eventually rid ourselves of
> struct_mutex recursion!)
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/i915_drv.h          |  2 +-
>  drivers/gpu/drm/i915/i915_gem_gtt.c      | 10 ++++++++++
>  drivers/gpu/drm/i915/i915_gem_gtt.h      |  2 ++
>  drivers/gpu/drm/i915/i915_gem_shrinker.c | 12 ++++++++++++
>  4 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index eeb002a47032..01dd29837233 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3304,7 +3304,7 @@ unsigned long i915_gem_shrink(struct drm_i915_private *i915,
>  unsigned long i915_gem_shrink_all(struct drm_i915_private *i915);
>  void i915_gem_shrinker_register(struct drm_i915_private *i915);
>  void i915_gem_shrinker_unregister(struct drm_i915_private *i915);
> -
> +void i915_gem_shrinker_taints_mutex(struct mutex *mutex);
>  
>  /* i915_gem_tiling.c */
>  static inline bool i915_gem_object_needs_bit17_swizzle(struct drm_i915_gem_object *obj)
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index abd81fb9b0b6..d0acef299b9c 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -531,6 +531,14 @@ static void vm_free_page(struct i915_address_space *vm, struct page *page)
>  static void i915_address_space_init(struct i915_address_space *vm,
>  				    struct drm_i915_private *dev_priv)
>  {
> +	/*
> +	 * The vm->mutex must be reclaim safe (for use in the shrinker).
> +	 * Do a dummy acquire now under fs_reclaim so that any allocation
> +	 * attempt holding the lock is immediately reported by lockdep.
> +	 */
> +	mutex_init(&vm->mutex);
> +	i915_gem_shrinker_taints_mutex(&vm->mutex);
> +
>  	GEM_BUG_ON(!vm->total);
>  	drm_mm_init(&vm->mm, 0, vm->total);
>  	vm->mm.head_node.color = I915_COLOR_UNEVICTABLE;
> @@ -551,6 +559,8 @@ static void i915_address_space_fini(struct i915_address_space *vm)
>  	spin_unlock(&vm->free_pages.lock);
>  
>  	drm_mm_takedown(&vm->mm);
> +
> +	mutex_destroy(&vm->mutex);
>  }
>  
>  static int __setup_page_dma(struct i915_address_space *vm,
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.h b/drivers/gpu/drm/i915/i915_gem_gtt.h
> index feda45dfd481..14e62651010b 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.h
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.h
> @@ -293,6 +293,8 @@ struct i915_address_space {
>  
>  	bool closed;
>  
> +	struct mutex mutex; /* protects vma and our lists */
> +
>  	struct i915_page_dma scratch_page;
>  	struct i915_page_table *scratch_pt;
>  	struct i915_page_directory *scratch_pd;
> diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> index c61f5b80fee3..ea90d3a0d511 100644
> --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c
> @@ -23,6 +23,7 @@
>   */
>  
>  #include <linux/oom.h>
> +#include <linux/sched/mm.h>
>  #include <linux/shmem_fs.h>
>  #include <linux/slab.h>
>  #include <linux/swap.h>
> @@ -531,3 +532,14 @@ void i915_gem_shrinker_unregister(struct drm_i915_private *i915)
>  	WARN_ON(unregister_oom_notifier(&i915->mm.oom_notifier));
>  	unregister_shrinker(&i915->mm.shrinker);
>  }
> +
> +void i915_gem_shrinker_taints_mutex(struct mutex *mutex)
> +{
> +	if (!IS_ENABLED(CONFIG_LOCKDEP))
> +		return;
> +
> +	fs_reclaim_acquire(GFP_KERNEL);
> +	mutex_lock(mutex);
> +	mutex_unlock(mutex);
> +	fs_reclaim_release(GFP_KERNEL);
> +}
> -- 
> 2.18.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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