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

[Daniel Vetter]

On Wed, Nov 20, 2019 at 3:07 AM Rob Clark <robdclark at gmail.com> wrote:
>
> 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

I'll add a comment.

> with that, r-b

Well I spotted a bug for the error handling, I'll need to respin.
-Daniel

>
> >
> > 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
> >



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch