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

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Nov 20, 2019 at 04:24:48PM -0800, Rob Clark wrote:
> On Wed, Nov 20, 2019 at 2:56 AM Daniel Vetter <daniel.vetter@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.
> >
> > Aside: Why is msm still using struct_mutex, it seems to be using
> > dma_resv_lock for general buffer state protection?
> >
> > v2:
> > - Add comment to explain why the ww ticket setup is separate (Rob)
> > - Fix up error handling, we need to make sure we don't call
> >   ww_acquire_fini without _init.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Rob Clark <robdclark@gmail.com>
> > Cc: Sean Paul <sean@poorly.run>
> > Cc: linux-arm-msm@vger.kernel.org
> > Cc: freedreno@lists.freedesktop.org
> 
> found a few minutes to take this for a spin and seems fine.. t-b && r-b

Thanks for taking this for a spin, entire series applied.
-Daniel

> 
> BR,
> -R
> 
> > ---
> >  drivers/gpu/drm/msm/msm_gem_submit.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
> > index fb1fdd7fa3ef..385d4965a8d0 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;
> >  }
> > @@ -390,8 +389,6 @@ static void submit_cleanup(struct msm_gem_submit *submit)
> >                 list_del_init(&msm_obj->submit_entry);
> >                 drm_gem_object_put(&msm_obj->base);
> >         }
> > -
> > -       ww_acquire_fini(&submit->ticket);
> >  }
> >
> >  int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> > @@ -408,6 +405,7 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> >         struct msm_ringbuffer *ring;
> >         int out_fence_fd = -1;
> >         struct pid *pid = get_pid(task_pid(current));
> > +       bool has_ww_ticket = false;
> >         unsigned i;
> >         int ret, submitid;
> >         if (!gpu)
> > @@ -489,6 +487,9 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> >         if (ret)
> >                 goto out;
> >
> > +       /* copy_*_user while holding a ww ticket upsets lockdep */
> > +       ww_acquire_init(&submit->ticket, &reservation_ww_class);
> > +       has_ww_ticket = true;
> >         ret = submit_lock_objects(submit);
> >         if (ret)
> >                 goto out;
> > @@ -588,6 +589,8 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
> >
> >  out:
> >         submit_cleanup(submit);
> > +       if (has_ww_ticket)
> > +               ww_acquire_fini(&submit->ticket);
> >         if (ret)
> >                 msm_gem_submit_free(submit);
> >  out_unlock:
> > --
> > 2.24.0
> >

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch