[Intel-xe] [PATCH v5 5/7] drm/xe/ggtt: prime ggtt->lock against FS_RECLAIM

[Rodrigo Vivi]

On Wed, May 17, 2023 at 04:22:42PM +0100, Matthew Auld wrote:
> Increase the sensitivity of the ggtt->lock by priming it against
> FS_RECLAIM, such that allocating memory while holding will result in
> lockdep splats.
> 
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> ---
>  drivers/gpu/drm/xe/xe_ggtt.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_ggtt.c b/drivers/gpu/drm/xe/xe_ggtt.c
> index f986e8218820..e25eb70d44f6 100644
> --- a/drivers/gpu/drm/xe/xe_ggtt.c
> +++ b/drivers/gpu/drm/xe/xe_ggtt.c
> @@ -90,6 +90,16 @@ static void ggtt_fini_noalloc(struct drm_device *drm, void *arg)
>  	xe_bo_unpin_map_no_vm(ggtt->scratch);
>  }
>  
> +static void primelockdep(struct xe_ggtt *ggtt)
> +{
> +	if (!IS_ENABLED(CONFIG_LOCKDEP))
> +		return;
> +
> +	fs_reclaim_acquire(GFP_KERNEL);
> +	might_lock(&ggtt->lock);
> +	fs_reclaim_release(GFP_KERNEL);

should we use the might_alloc instead of these fs_reclaim directly?
or the order here with the ggtt->lock in the middle matters?

> +}
> +
>  int xe_ggtt_init_noalloc(struct xe_gt *gt, struct xe_ggtt *ggtt)
>  {
>  	struct xe_device *xe = gt_to_xe(gt);
> @@ -132,6 +142,7 @@ int xe_ggtt_init_noalloc(struct xe_gt *gt, struct xe_ggtt *ggtt)
>  	drm_mm_init(&ggtt->mm, xe_wopcm_size(xe),
>  		    ggtt->size - xe_wopcm_size(xe));
>  	mutex_init(&ggtt->lock);
> +	primelockdep(ggtt);
>  
>  	return drmm_add_action_or_reset(&xe->drm, ggtt_fini_noalloc, ggtt);
>  }
> -- 
> 2.40.1
>