[PATCH] drm/ttm: fix fence locking in ttm_buffer_object_transfer, 2nd try

[Maarten Lankhorst]

Op 14-01-13 15:08, Daniel Vetter schreef:
> This fixes up
>
> commit e8e89622ed361c46bf90ba4828e685a8b603f7e5
> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> Date:   Tue Dec 18 22:25:11 2012 +0100
>
>     drm/ttm: fix fence locking in ttm_buffer_object_transfer
>
> which leaves behind a might_sleep in atomic context, since the
> fence_lock spinlock is held over a kmalloc(GFP_KERNEL) call. The fix
> is to revert the above commit and only take the lock where we need it,
> around the call to ->sync_obj_ref.
>
> v2: Fixup things noticed by Maarten Lankhorst:
> - Brown paper bag locking bug.
> - No need for kzalloc if we clear the entire thing on the next line.
> - check for bo->sync_obj (totally unlikely race, but still someone
>   else could have snuck in) and clear fbo->sync_obj if it's cleared
>   already.
>
> Reported-by: Dave Airlie <airlied at gmail.com>
> Cc: Jerome Glisse <jglisse at redhat.com>
> Cc: Maarten Lankhorst <maarten.lankhorst at canonical.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst at canonical.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/ttm/ttm_bo_util.c |   13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index d73d6e3..544e407 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -422,7 +422,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
>  	struct ttm_bo_device *bdev = bo->bdev;
>  	struct ttm_bo_driver *driver = bdev->driver;
>  
> -	fbo = kzalloc(sizeof(*fbo), GFP_KERNEL);
> +	fbo = kmalloc(sizeof(*fbo), GFP_KERNEL);
>  	if (!fbo)
>  		return -ENOMEM;
>  
> @@ -441,7 +441,12 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
>  	fbo->vm_node = NULL;
>  	atomic_set(&fbo->cpu_writers, 0);
>  
> -	fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
> +	spin_lock(&bdev->fence_lock);
> +	if (bo->sync_obj)
> +		fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
> +	else
> +		fbo->sync_obj = NULL;
> +	spin_unlock(&bdev->fence_lock);
>  	kref_init(&fbo->list_kref);
>  	kref_init(&fbo->kref);
>  	fbo->destroy = &ttm_transfered_destroy;
> @@ -654,13 +659,11 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
>  		 */
>  
>  		set_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
> -
> -		/* ttm_buffer_object_transfer accesses bo->sync_obj */
> -		ret = ttm_buffer_object_transfer(bo, &ghost_obj);
>  		spin_unlock(&bdev->fence_lock);
>  		if (tmp_obj)
>  			driver->sync_obj_unref(&tmp_obj);
>  
> +		ret = ttm_buffer_object_transfer(bo, &ghost_obj);
>  		if (ret)
>  			return ret;
>