Re: [PATCH v6 12/12] drm/xe/bo: Skip zero-refcount BOs in shrinker

Yadav, Arvind
2026-03-17T05:59:58Z

On 05-03-2026 21:19, Thomas Hellström wrote:
> On Tue, 2026-03-03 at 20:50 +0530, Arvind Yadav wrote:
>> Zero-refcount BOs are being destroyed. Skip them in the shrinker
>> to avoid racing with cleanup by returning -EBUSY.
>>
>> Ghost BOs from ttm_bo_pipeline_gutting() still hold reclaimable
>> pages, so continue processing them via xe_bo_shrink_purge().
>>
>> Fixes: 00c8efc3180f ("drm/xe: Add a shrinker for xe bos")
>>
>> v6:
>>   - Split from patch 0010 (Thomas)
>>
>> Cc: Matthew Brost <matthew.brost@intel.com>
>> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>> Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
> Hi, Arvind.
>
>> ---
>>  drivers/gpu/drm/xe/xe_bo.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index 598d4463baf3..07acce383cb1 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -1295,9 +1295,13 @@ long xe_bo_shrink(struct ttm_operation_ctx
>> *ctx, struct ttm_buffer_object *bo,
>>   if (!xe_bo_eviction_valuable(bo, &place))
>>   return -EBUSY;
>>
>> - if (!xe_bo_is_xe_bo(bo) || !xe_bo_get_unless_zero(xe_bo))
> Looking a bit closer at this, I realized this is intentional. The bo
> has two refcounts. One is the gem refcount (which we fail to grab here)
> and one is the ttm refcount, which we have successfully grabbed,
> otherwise this function wouldn't be called. So the bo is in a zombie
> state (all xe-specific members are invalidd) but calling
> xe_bo_shrink_purge is allowed. So this patch could actually be dropped.
>
> Question is did you see any issues from xe_bo_shrink_purge() without
> this patch?

I did not see a concrete crash or corruption from xe_bo_shrink_purge()
on a zombie BO — the patch was added as a precaution based on the
refcount check pattern.
Given your analysis, I'll drop this patch in v7.

Thanks,
Arvind

>
> Thanks,
> Thomas