Re: [RFC 01/17] dma-fence: add might_sleep annotation to _wait()

[Christian KÃnig]

Am 12.05.20 um 10:59 schrieb Daniel Vetter:
> But only for non-zero timeout, to avoid false positives.
>
> One question here is whether the might_sleep should be unconditional,
> or only for real timeouts. I'm not sure, so went with the more
> defensive option. But in the interest of locking down the cross-driver
> dma_fence rules we might want to be more aggressive.
>
> Cc: linux-media@xxxxxxxxxxxxxxx
> Cc: linaro-mm-sig@xxxxxxxxxxxxxxxx
> Cc: linux-rdma@xxxxxxxxxxxxxxx
> Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> Cc: Christian KÃnig <christian.koenig@xxxxxxx>
> Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> ---
>   drivers/dma-buf/dma-fence.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 052a41e2451c..6802125349fb 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -208,6 +208,9 @@ dma_fence_wait_timeout(struct dma_fence *fence, bool intr, signed long timeout)
>   	if (WARN_ON(timeout < 0))
>   		return -EINVAL;
>   
> +	if (timeout > 0)
> +		might_sleep();
> +

I would rather like to see might_sleep() called here all the time even 
with timeout==0.

IIRC I removed the code in TTM abusing this in atomic context quite a 
while ago, but could be that some leaked in again or it is called in 
atomic context elsewhere as well.

Christian.

>   	trace_dma_fence_wait_start(fence);
>   	if (fence->ops->wait)
>   		ret = fence->ops->wait(fence, intr, timeout);