[PATCH v2] drm/syncobj: Deal with signalled fences in drm_syncobj_find_fence.

[Lionel Landwerlin]

On 08/12/2021 11:28, Christian König wrote:
> Am 08.12.21 um 03:39 schrieb Bas Nieuwenhuizen:
>> dma_fence_chain_find_seqno only ever returns the top fence in the
>> chain or an unsignalled fence. Hence if we request a seqno that
>> is already signalled it returns a NULL fence. Some callers are
>> not prepared to handle this, like the syncobj transfer functions
>> for example.
>>
>> This behavior is "new" with timeline syncobj and it looks like
>> not all callers were updated. To fix this behavior make sure
>> that a successful drm_sync_find_fence always returns a non-NULL
>> fence.
>>
>> v2: Move the fix to drm_syncobj_find_fence from the transfer
>>      functions.
>>
>> Fixes: ea569910cbab ("drm/syncobj: add transition iotcls between 
>> binary and timeline v2")
>> Cc: stable at vger.kernel.org
>> Signed-off-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>
>
> Reviewed-by: Christian König <christian.koenig at amd.com>


Thanks!


Acked-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>


>
>> ---
>>   drivers/gpu/drm/drm_syncobj.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_syncobj.c 
>> b/drivers/gpu/drm/drm_syncobj.c
>> index fdd2ec87cdd1..11be91b5709b 100644
>> --- a/drivers/gpu/drm/drm_syncobj.c
>> +++ b/drivers/gpu/drm/drm_syncobj.c
>> @@ -404,8 +404,17 @@ int drm_syncobj_find_fence(struct drm_file 
>> *file_private,
>>         if (*fence) {
>>           ret = dma_fence_chain_find_seqno(fence, point);
>> -        if (!ret)
>> +        if (!ret) {
>> +            /* If the requested seqno is already signaled
>> +             * drm_syncobj_find_fence may return a NULL
>> +             * fence. To make sure the recipient gets
>> +             * signalled, use a new fence instead.
>> +             */
>> +            if (!*fence)
>> +                *fence = dma_fence_get_stub();
>> +
>>               goto out;
>> +        }
>>           dma_fence_put(*fence);
>>       } else {
>>           ret = -EINVAL;
>