[PATCH 3/3] drm/msm: Don't init ww_mutec acquire ctx before needed

[Rob Clark]

On Tue, Nov 19, 2019 at 1:08 PM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> For locking semantics it really doesn't matter when we grab the
> ticket. But for lockdep validation it does: the acquire ctx is a fake
> lockdep. Since other drivers might want to do a full multi-lock dance
> in their fault-handler, not just lock a single dma_resv. Therefore we
> must init the acquire_ctx only after we've done all the copy_*_user or
> anything else that might trigger a pagefault. For msm this means we
> need to move it past submit_lookup_objects.

seems reasonable.. but maybe a comment would be useful to prevent
future-me from "cleaning-this-up" back to the way it was

with that, r-b

>
> Aside: Why is msm still using struct_mutex, it seems to be using
> dma_resv_lock for general buffer state protection?

only because I (or anyone else) hasn't had time to revisit the
struct_mutex usage since we moved to per-object-locks.. the downside,
I suppose, of kernel generally working ok and this not being a big
enough fire to bubble up to the top of my todo list

BR,
-R

>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: Sean Paul <sean at poorly.run>
> Cc: linux-arm-msm at vger.kernel.org
> Cc: freedreno at lists.freedesktop.org
> ---
>  drivers/gpu/drm/msm/msm_gem_submit.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> index fb1fdd7fa3ef..126b2f62bfe7 100644
> --- a/drivers/gpu/drm/msm/msm_gem_submit.c
> +++ b/drivers/gpu/drm/msm/msm_gem_submit.c
> @@ -54,7 +54,6 @@ static struct msm_gem_submit *submit_create(struct drm_device *dev,
>
>         INIT_LIST_HEAD(&submit->node);
>         INIT_LIST_HEAD(&submit->bo_list);
> -       ww_acquire_init(&submit->ticket, &reservation_ww_class);
>
>         return submit;
>  }
> @@ -489,6 +488,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
>         if (ret)
>                 goto out;
>
> +       ww_acquire_init(&submit->ticket, &reservation_ww_class);
>         ret = submit_lock_objects(submit);
>         if (ret)
>                 goto out;
> --
> 2.24.0
>