Re: [PATCH] i915: Add support for drm syncobjs

On Thu, Aug 3, 2017 at 11:15 AM, Chris Wilson chris@chris-wilson.co.uk wrote:

Quoting Jason Ekstrand (2017-08-03 19:06:02)

...

I'm not concerned about what happens to racy clients. They get what

they get.

...

What concerns me is what happens if somehow the fence is replaced and

deleted

...

before i915_gem_request_await_dma_fence takes it's reference. Can this

cause

...

the kernel to segfault?

Gotcha, yup nothing prevents that.

    fence = dma_fence_get_rcu_safe(&syncobj->fence);
    if (!fence)
            return -EINVAL;

    err = await_fence();
    dma_fence_put(fence);
    if (err < 0)
            return;

Happy?

Assuming dma_fence_get_rcu_safe does what I think it does, then yes.