[PATCH] drm/amdgpu: keep the MMU lock until the update ends v3

[Felix Kuehling]

Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com>

Thanks,
  Felix


On 2017-09-07 06:11 AM, Christian König wrote:
> From: Christian König <christian.koenig at amd.com>
>
> This is quite controversial because it adds another lock which is held during
> page table updates, but I don't see much other option.
>
> v2: allow multiple updates to be in flight at the same time
> v3: simplify the patch, take the read side only once
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> Reviewed-by: Felix Kuehling <Felix.Kuehling at amd.com> (v1)
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu.h    |  4 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c | 78 ++++++++++++++++++++++++++++++++--
>  2 files changed, 76 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> index 0f2d903..28fae72 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> @@ -1202,11 +1202,11 @@ void amdgpu_test_moves(struct amdgpu_device *adev);
>   * MMU Notifier
>   */
>  #if defined(CONFIG_MMU_NOTIFIER)
> +void amdgpu_mn_lock(struct amdgpu_mn *mn);
> +void amdgpu_mn_unlock(struct amdgpu_mn *mn);
>  struct amdgpu_mn *amdgpu_mn_get(struct amdgpu_device *adev);
>  int amdgpu_mn_register(struct amdgpu_bo *bo, unsigned long addr);
>  void amdgpu_mn_unregister(struct amdgpu_bo *bo);
> -void amdgpu_mn_lock(struct amdgpu_mn *mn);
> -void amdgpu_mn_unlock(struct amdgpu_mn *mn);
>  #else
>  static inline void amdgpu_mn_lock(struct amdgpu_mn *mn) {}
>  static inline void amdgpu_mn_unlock(struct amdgpu_mn *mn) {}
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
> index 99edb40..89743bb 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mn.c
> @@ -52,6 +52,8 @@ struct amdgpu_mn {
>  	/* objects protected by lock */
>  	struct rw_semaphore	lock;
>  	struct rb_root		objects;
> +	struct mutex		read_lock;
> +	atomic_t		recursion;
>  };
>  
>  struct amdgpu_mn_node {
> @@ -126,6 +128,53 @@ void amdgpu_mn_unlock(struct amdgpu_mn *mn)
>  }
>  
>  /**
> + * amdgpu_mn_read_lock - take the rmn read lock
> + *
> + * @rmn: our notifier
> + *
> + * Take the rmn read side lock.
> + */
> +static void amdgpu_mn_read_lock(struct amdgpu_mn *rmn)
> +{
> +	mutex_lock(&rmn->read_lock);
> +	if (atomic_inc_return(&rmn->recursion) == 1)
> +		down_read_non_owner(&rmn->lock);
> +	mutex_unlock(&rmn->read_lock);
> +}
> +
> +/**
> + * amdgpu_mn_read_unlock - drop the rmn read lock
> + *
> + * @rmn: our notifier
> + *
> + * Drop the rmn read side lock.
> + */
> +static void amdgpu_mn_read_unlock(struct amdgpu_mn *rmn)
> +{
> +	if (atomic_dec_return(&rmn->recursion) == 0)
> +		up_read_non_owner(&rmn->lock);
> +}
> +
> +
> +/**
> + * amdgpu_mn_lock - take the write side lock of this mn
> + */
> +void amdgpu_mn_lock(struct amdgpu_mn *mn)
> +{
> +	if (mn)
> +		down_write(&mn->lock);
> +}
> +
> +/**
> + * amdgpu_mn_unlock - drop the write side lock for this mn
> + */
> +void amdgpu_mn_unlock(struct amdgpu_mn *mn)
> +{
> +	if (mn)
> +		up_write(&mn->lock);
> +}
> +
> +/**
>   * amdgpu_mn_invalidate_node - unmap all BOs of a node
>   *
>   * @node: the node with the BOs to unmap
> @@ -171,7 +220,7 @@ static void amdgpu_mn_invalidate_page(struct mmu_notifier *mn,
>  	struct amdgpu_mn *rmn = container_of(mn, struct amdgpu_mn, mn);
>  	struct interval_tree_node *it;
>  
> -	down_read(&rmn->lock);
> +	amdgpu_mn_read_lock(rmn);
>  
>  	it = interval_tree_iter_first(&rmn->objects, address, address);
>  	if (it) {
> @@ -181,7 +230,7 @@ static void amdgpu_mn_invalidate_page(struct mmu_notifier *mn,
>  		amdgpu_mn_invalidate_node(node, address, address);
>  	}
>  
> -	up_read(&rmn->lock);
> +	amdgpu_mn_read_unlock(rmn);
>  }
>  
>  /**
> @@ -206,7 +255,7 @@ static void amdgpu_mn_invalidate_range_start(struct mmu_notifier *mn,
>  	/* notification is exclusive, but interval is inclusive */
>  	end -= 1;
>  
> -	down_read(&rmn->lock);
> +	amdgpu_mn_read_lock(rmn);
>  
>  	it = interval_tree_iter_first(&rmn->objects, start, end);
>  	while (it) {
> @@ -217,14 +266,33 @@ static void amdgpu_mn_invalidate_range_start(struct mmu_notifier *mn,
>  
>  		amdgpu_mn_invalidate_node(node, start, end);
>  	}
> +}
> +
> +/**
> + * amdgpu_mn_invalidate_range_end - callback to notify about mm change
> + *
> + * @mn: our notifier
> + * @mn: the mm this callback is about
> + * @start: start of updated range
> + * @end: end of updated range
> + *
> + * Release the lock again to allow new command submissions.
> + */
> +static void amdgpu_mn_invalidate_range_end(struct mmu_notifier *mn,
> +					   struct mm_struct *mm,
> +					   unsigned long start,
> +					   unsigned long end)
> +{
> +	struct amdgpu_mn *rmn = container_of(mn, struct amdgpu_mn, mn);
>  
> -	up_read(&rmn->lock);
> +	amdgpu_mn_read_unlock(rmn);
>  }
>  
>  static const struct mmu_notifier_ops amdgpu_mn_ops = {
>  	.release = amdgpu_mn_release,
>  	.invalidate_page = amdgpu_mn_invalidate_page,
>  	.invalidate_range_start = amdgpu_mn_invalidate_range_start,
> +	.invalidate_range_end = amdgpu_mn_invalidate_range_end,
>  };
>  
>  /**
> @@ -261,6 +329,8 @@ struct amdgpu_mn *amdgpu_mn_get(struct amdgpu_device *adev)
>  	rmn->mn.ops = &amdgpu_mn_ops;
>  	init_rwsem(&rmn->lock);
>  	rmn->objects = RB_ROOT;
> +	mutex_init(&rmn->read_lock);
> +	atomic_set(&rmn->recursion, 0);
>  
>  	r = __mmu_notifier_register(&rmn->mn, mm);
>  	if (r)