On Tue, Nov 20, 2018 at 02:04:14PM -0800, Jeykumar Sankaran wrote:
> On 2018-11-07 07:55, Sean Paul wrote:
> > On Tue, Nov 06, 2018 at 02:36:30PM -0800, Jeykumar Sankaran wrote:
> > > msm maintains a separate structure to define vblank
> > > work definitions and a list to track events submitted
> > > to the workqueue. We can avoid this redundant list
> > > and its protection mechanism, if we subclass the
> > > work object to encapsulate vblank event parameters.
> > >
> > > changes in v2:
> > > - subclass optimization on system wq (Sean Paul)
> >
> > I wouldn't do it like this, tbh. One problem is that you've lost your
> > flush() on
> > unbind, so there's no way to know if you have workers in the wild
> > waiting
> > to
> > enable/disable vblank.
> >
> > Another issues is that AFAICT, we don't need a queue of
> > enables/disables,
> > but
> > rather just the last requested state (ie: should we be on or off). So
> > things
> > don't need to be this complicated (and we're possibly thrashing vblank
> > on/off
> > for no reason).
> >
> > I'm still of the mind that you should just make this synchronous and be
> > done
> > with the threads (especially since we're still uncovering/introducing
> > races!).
> >
> While scoping out the effort to make vblank events synchronous, I found
> that the spinlock locking order of vblank request sequence and vblank
> callback
> sequences are the opposite.
>
> In DPU, drm_vblank_enable acquires vblank_time_lock before registering
> the crtc to encoder which happens after acquiring encoder_spinlock. But
> the vblank_callback acquires encoder_spinlock before accessing the
> registered
> crtc and calling into drm_vblank_handler which tries to acquire
> vblank_time_lock.
> Acquiring both vblank_time_lock and encoder_spinlock in the same thread
> is leading to deadlock.
Hmm, I'm not sure I follow. Are you seeing issues where irq overlaps with
enable/disable? I hacked in sync vblank enable/disable quickly to see if I could
reproduce what you're seeing, but things seemed well behaved.
I do see that there is a chance to call drm_handle_vblank() while holding
enc_spinlock, but couldn't find any obvious lock recursion there.
Maybe a callstack or lockdep splat would help?
Sean
Here's my hack to bypass the display thread:
diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 9c9f7ff6960b38..5a3cac5825319e 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -242,24 +242,19 @@ static void vblank_ctrl_worker(struct kthread_work *work)
static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
int crtc_id, bool enable)
{
+ struct msm_kms *kms = priv->kms;
struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
- struct vblank_event *vbl_ev;
unsigned long flags;
- vbl_ev = kzalloc(sizeof(*vbl_ev), GFP_ATOMIC);
- if (!vbl_ev)
- return -ENOMEM;
+ spin_lock_irqsave(&vbl_ctrl->lock, flags);
- vbl_ev->crtc_id = crtc_id;
- vbl_ev->enable = enable;
+ if (enable)
+ kms->funcs->enable_vblank(kms, priv->crtcs[crtc_id]);
+ else
+ kms->funcs->disable_vblank(kms, priv->crtcs[crtc_id]);
- spin_lock_irqsave(&vbl_ctrl->lock, flags);
- list_add_tail(&vbl_ev->node, &vbl_ctrl->event_list);
spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
- kthread_queue_work(&priv->disp_thread[crtc_id].worker,
- &vbl_ctrl->work);
-
return 0;
}
>
> In MDP5, I see the same pattern between vblank_time_lock and list_lock which
> is used to track the irq handlers.
>
> I believe that explains why msm_drv is queuing the vblank enable/disable
> works to WQ after acquiring vblank_time_lock.
>
> Thanks,
> Jeykumar S.
>
> > Sean
> >
> > >
> > > Signed-off-by: Jeykumar Sankaran <jsanka@xxxxxxxxxxxxxx>
> > > ---
> > > drivers/gpu/drm/msm/msm_drv.c | 67
> > +++++++++++++------------------------------
> > > drivers/gpu/drm/msm/msm_drv.h | 7 -----
> > > 2 files changed, 20 insertions(+), 54 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_drv.c
> > b/drivers/gpu/drm/msm/msm_drv.c
> > > index 6d6c73b..8da5be2 100644
> > > --- a/drivers/gpu/drm/msm/msm_drv.c
> > > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > > @@ -203,61 +203,44 @@ u32 msm_readl(const void __iomem *addr)
> > > return val;
> > > }
> > >
> > > -struct vblank_event {
> > > - struct list_head node;
> > > +struct msm_vblank_work {
> > > + struct work_struct work;
> > > int crtc_id;
> > > bool enable;
> > > + struct msm_drm_private *priv;
> > > };
> > >
> > > static void vblank_ctrl_worker(struct work_struct *work)
> > > {
> > > - struct msm_vblank_ctrl *vbl_ctrl = container_of(work,
> > > - struct msm_vblank_ctrl,
> > work);
> > > - struct msm_drm_private *priv = container_of(vbl_ctrl,
> > > - struct msm_drm_private,
> > vblank_ctrl);
> > > + struct msm_vblank_work *vbl_work = container_of(work,
> > > + struct msm_vblank_work,
> > work);
> > > + struct msm_drm_private *priv = vbl_work->priv;
> > > struct msm_kms *kms = priv->kms;
> > > - struct vblank_event *vbl_ev, *tmp;
> > > - unsigned long flags;
> > > -
> > > - spin_lock_irqsave(&vbl_ctrl->lock, flags);
> > > - list_for_each_entry_safe(vbl_ev, tmp, &vbl_ctrl->event_list, node)
> > {
> > > - list_del(&vbl_ev->node);
> > > - spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> > > -
> > > - if (vbl_ev->enable)
> > > - kms->funcs->enable_vblank(kms,
> > > -
> > priv->crtcs[vbl_ev->crtc_id]);
> > > - else
> > > - kms->funcs->disable_vblank(kms,
> > > -
> > priv->crtcs[vbl_ev->crtc_id]);
> > >
> > > - kfree(vbl_ev);
> > > -
> > > - spin_lock_irqsave(&vbl_ctrl->lock, flags);
> > > - }
> > > + if (vbl_work->enable)
> > > + kms->funcs->enable_vblank(kms,
> > priv->crtcs[vbl_work->crtc_id]);
> > > + else
> > > + kms->funcs->disable_vblank(kms,
> > priv->crtcs[vbl_work->crtc_id]);
> > >
> > > - spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> > > + kfree(vbl_work);
> > > }
> > >
> > > static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
> > > int crtc_id, bool enable)
> > > {
> > > - struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
> > > - struct vblank_event *vbl_ev;
> > > - unsigned long flags;
> > > + struct msm_vblank_work *vbl_work;
> > >
> > > - vbl_ev = kzalloc(sizeof(*vbl_ev), GFP_ATOMIC);
> > > - if (!vbl_ev)
> > > + vbl_work = kzalloc(sizeof(*vbl_work), GFP_ATOMIC);
> > > + if (!vbl_work)
> > > return -ENOMEM;
> > >
> > > - vbl_ev->crtc_id = crtc_id;
> > > - vbl_ev->enable = enable;
> > > + INIT_WORK(&vbl_work->work, vblank_ctrl_worker);
> > >
> > > - spin_lock_irqsave(&vbl_ctrl->lock, flags);
> > > - list_add_tail(&vbl_ev->node, &vbl_ctrl->event_list);
> > > - spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> > > + vbl_work->crtc_id = crtc_id;
> > > + vbl_work->enable = enable;
> > > + vbl_work->priv = priv;
> > >
> > > - schedule_work(&vbl_ctrl->work);
> > > + schedule_work(&vbl_work->work);
> > >
> > > return 0;
> > > }
> > > @@ -269,14 +252,13 @@ static int msm_drm_uninit(struct device *dev)
> > > struct msm_drm_private *priv = ddev->dev_private;
> > > struct msm_kms *kms = priv->kms;
> > > struct msm_mdss *mdss = priv->mdss;
> > > - struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
> > > - struct vblank_event *vbl_ev, *tmp;
> > > int i;
> > >
> > > /* We must cancel and cleanup any pending vblank enable/disable
> > > * work before drm_irq_uninstall() to avoid work re-enabling an
> > > * irq after uninstall has disabled it.
> > > */
> > > +
> > > msm_gem_shrinker_cleanup(ddev);
> > >
> > > drm_kms_helper_poll_fini(ddev);
> > > @@ -292,12 +274,6 @@ static int msm_drm_uninit(struct device *dev)
> > > #endif
> > > drm_mode_config_cleanup(ddev);
> > >
> > > - flush_work(&vbl_ctrl->work);
> > > - list_for_each_entry_safe(vbl_ev, tmp, &vbl_ctrl->event_list, node)
> > {
> > > - list_del(&vbl_ev->node);
> > > - kfree(vbl_ev);
> > > - }
> > > -
> > > /* clean up event worker threads */
> > > for (i = 0; i < priv->num_crtcs; i++) {
> > > if (priv->event_thread[i].thread) {
> > > @@ -469,9 +445,6 @@ static int msm_drm_init(struct device *dev, struct
> > drm_driver *drv)
> > > priv->wq = alloc_ordered_workqueue("msm", 0);
> > >
> > > INIT_LIST_HEAD(&priv->inactive_list);
> > > - INIT_LIST_HEAD(&priv->vblank_ctrl.event_list);
> > > - INIT_WORK(&priv->vblank_ctrl.work, vblank_ctrl_worker);
> > > - spin_lock_init(&priv->vblank_ctrl.lock);
> > >
> > > drm_mode_config_init(ddev);
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_drv.h
> > b/drivers/gpu/drm/msm/msm_drv.h
> > > index 05d33a7..d4cbde2 100644
> > > --- a/drivers/gpu/drm/msm/msm_drv.h
> > > +++ b/drivers/gpu/drm/msm/msm_drv.h
> > > @@ -77,12 +77,6 @@ enum msm_mdp_plane_property {
> > > PLANE_PROP_MAX_NUM
> > > };
> > >
> > > -struct msm_vblank_ctrl {
> > > - struct work_struct work;
> > > - struct list_head event_list;
> > > - spinlock_t lock;
> > > -};
> > > -
> > > #define MSM_GPU_MAX_RINGS 4
> > > #define MAX_H_TILES_PER_DISPLAY 2
> > >
> > > @@ -225,7 +219,6 @@ struct msm_drm_private {
> > > struct notifier_block vmap_notifier;
> > > struct shrinker shrinker;
> > >
> > > - struct msm_vblank_ctrl vblank_ctrl;
> > > struct drm_atomic_state *pm_state;
> > > };
> > >
> > > --
> > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
> > Forum,
> > > a Linux Foundation Collaborative Project
> > >
> > > _______________________________________________
> > > Freedreno mailing list
> > > Freedreno@xxxxxxxxxxxxxxxxxxxxx
> > > https://lists.freedesktop.org/mailman/listinfo/freedreno
>
> --
> Jeykumar S
--
Sean Paul, Software Engineer, Google / Chromium OS
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