linux-kernel - Re: [RFC 01/17] dma-fence: add might_sleep annotation to

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Date:   Tue, 12 May 2020 11:08:22 +0200
From:   Christian König <christian.koenig@....com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-rdma@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [RFC 01/17] dma-fence: add might_sleep annotation to _wait()

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@...r.kernel.org
> Cc: linaro-mm-sig@...ts.linaro.org
> Cc: linux-rdma@...r.kernel.org
> Cc: amd-gfx@...ts.freedesktop.org
> Cc: intel-gfx@...ts.freedesktop.org
> Cc: Chris Wilson <chris@...is-wilson.co.uk>
> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> Cc: Christian König <christian.koenig@....com>
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> ---
>   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);