[resend PATCH] drm/ttm: Fix a deadlock if the target BO is not idle during swap

[Christian König]

Am 07.09.21 um 11:05 schrieb Daniel Vetter:
> On Tue, Sep 07, 2021 at 08:22:20AM +0200, Christian König wrote:
>> Added a Fixes tag and pushed this to drm-misc-fixes.
> We're in the merge window, this should have been drm-misc-next-fixes. I'll
> poke misc maintainers so it's not lost.

Hui? It's a fix for a problem in stable and not in drm-misc-next.

Christian.

> -Daniel
>
>> It will take a while until it cycles back into the development branches, so
>> feel free to push some version to amd-staging-drm-next as well. Just ping
>> Alex when you do this.
>>
>> Thanks,
>> Christian.
>>
>> Am 07.09.21 um 06:08 schrieb xinhui pan:
>>> The ret value might be -EBUSY, caller will think lru lock is still
>>> locked but actually NOT. So return -ENOSPC instead. Otherwise we hit
>>> list corruption.
>>>
>>> ttm_bo_cleanup_refs might fail too if BO is not idle. If we return 0,
>>> caller(ttm_tt_populate -> ttm_global_swapout ->ttm_device_swapout) will
>>> be stuck as we actually did not free any BO memory. This usually happens
>>> when the fence is not signaled for a long time.
>>>
>>> Signed-off-by: xinhui pan <xinhui.pan at amd.com>
>>> Reviewed-by: Christian König <christian.koenig at amd.com>
>>> ---
>>>    drivers/gpu/drm/ttm/ttm_bo.c | 6 +++---
>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
>>> index 8d7fd65ccced..23f906941ac9 100644
>>> --- a/drivers/gpu/drm/ttm/ttm_bo.c
>>> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
>>> @@ -1152,9 +1152,9 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
>>>    	}
>>>    	if (bo->deleted) {
>>> -		ttm_bo_cleanup_refs(bo, false, false, locked);
>>> +		ret = ttm_bo_cleanup_refs(bo, false, false, locked);
>>>    		ttm_bo_put(bo);
>>> -		return 0;
>>> +		return ret == -EBUSY ? -ENOSPC : ret;
>>>    	}
>>>    	ttm_bo_del_from_lru(bo);
>>> @@ -1208,7 +1208,7 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
>>>    	if (locked)
>>>    		dma_resv_unlock(bo->base.resv);
>>>    	ttm_bo_put(bo);
>>> -	return ret;
>>> +	return ret == -EBUSY ? -ENOSPC : ret;
>>>    }
>>>    void ttm_bo_tt_destroy(struct ttm_buffer_object *bo)