| Message ID | 20170317202030.24410-1-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, Mar 17, 2017 at 08:20:27PM +0000, Chris Wilson wrote: > Order the update to vblank->enabled after the timestamp is primed so > that a concurrent unlocked reader will only see the vblank->enabled with > the current timestamp. > > v2: vblank->enable is guarded by dev->vbl_lock not > dev->vblank_time_lock, update the READ_ONCE accordingly. The locking is indeed very confusing, and I don't know if it even makes sense anymore. But this looks at least as sane as anything else here :) For the series: Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> > > Do not add a READ_ONCE(vblank->enabled) inside the interrupt handler to > avoid missing an interrupt whilst racing with enable_vblank() > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch> > --- > drivers/gpu/drm/drm_irq.c | 23 ++++++++++++++--------- > 1 file changed, 14 insertions(+), 9 deletions(-) > > diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c > index 53a526c7b24d..c47e07c89136 100644 > --- a/drivers/gpu/drm/drm_irq.c > +++ b/drivers/gpu/drm/drm_irq.c > @@ -325,6 +325,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe) > struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; > unsigned long irqflags; > > + assert_spin_locked(&dev->vbl_lock); > + > /* Prevent vblank irq processing while disabling vblank irqs, > * so no updates of timestamps or count can happen after we've > * disabled. Needed to prevent races in case of delayed irq's. > @@ -336,10 +338,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe) > * calling the ->disable_vblank() operation in atomic context with the > * hardware potentially runtime suspended. > */ > - if (vblank->enabled) { > + if (cmpxchg_relaxed(&vblank->enabled, true, false)) > __disable_vblank(dev, pipe); > - vblank->enabled = false; > - } > > /* > * Always update the count and timestamp to maintain the > @@ -384,7 +384,7 @@ void drm_vblank_cleanup(struct drm_device *dev) > for (pipe = 0; pipe < dev->num_crtcs; pipe++) { > struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; > > - WARN_ON(vblank->enabled && > + WARN_ON(READ_ONCE(vblank->enabled) && > drm_core_check_feature(dev, DRIVER_MODESET)); > > del_timer_sync(&vblank->disable_timer); > @@ -1105,11 +1105,16 @@ static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe) > */ > ret = __enable_vblank(dev, pipe); > DRM_DEBUG("enabling vblank on crtc %u, ret: %d\n", pipe, ret); > - if (ret) > + if (ret) { > atomic_dec(&vblank->refcount); > - else { > - vblank->enabled = true; > + } else { > drm_update_vblank_count(dev, pipe, 0); > + /* drm_update_vblank_count() includes a wmb so we just > + * need to ensure that the compiler emits the write > + * to mark the vblank as enabled after the call > + * to drm_update_vblank_count(). > + */ > + WRITE_ONCE(vblank->enabled, true); > } > } > > @@ -1517,7 +1522,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe, > * vblank disable, so no need for further locking. The reference from > * drm_vblank_get() protects against vblank disable from another source. > */ > - if (!vblank->enabled) { > + if (!READ_ONCE(vblank->enabled)) { > ret = -EINVAL; > goto err_unlock; > } > @@ -1644,7 +1649,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data, > DRM_WAIT_ON(ret, vblank->queue, 3 * HZ, > (((drm_vblank_count(dev, pipe) - > vblwait->request.sequence) <= (1 << 23)) || > - !vblank->enabled || > + !READ_ONCE(vblank->enabled) || > !dev->irq_enabled)); > } > > -- > 2.11.0
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 53a526c7b24d..c47e07c89136 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -325,6 +325,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe) struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; unsigned long irqflags; + assert_spin_locked(&dev->vbl_lock); + /* Prevent vblank irq processing while disabling vblank irqs, * so no updates of timestamps or count can happen after we've * disabled. Needed to prevent races in case of delayed irq's. @@ -336,10 +338,8 @@ static void vblank_disable_and_save(struct drm_device *dev, unsigned int pipe) * calling the ->disable_vblank() operation in atomic context with the * hardware potentially runtime suspended. */ - if (vblank->enabled) { + if (cmpxchg_relaxed(&vblank->enabled, true, false)) __disable_vblank(dev, pipe); - vblank->enabled = false; - } /* * Always update the count and timestamp to maintain the @@ -384,7 +384,7 @@ void drm_vblank_cleanup(struct drm_device *dev) for (pipe = 0; pipe < dev->num_crtcs; pipe++) { struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; - WARN_ON(vblank->enabled && + WARN_ON(READ_ONCE(vblank->enabled) && drm_core_check_feature(dev, DRIVER_MODESET)); del_timer_sync(&vblank->disable_timer); @@ -1105,11 +1105,16 @@ static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe) */ ret = __enable_vblank(dev, pipe); DRM_DEBUG("enabling vblank on crtc %u, ret: %d\n", pipe, ret); - if (ret) + if (ret) { atomic_dec(&vblank->refcount); - else { - vblank->enabled = true; + } else { drm_update_vblank_count(dev, pipe, 0); + /* drm_update_vblank_count() includes a wmb so we just + * need to ensure that the compiler emits the write + * to mark the vblank as enabled after the call + * to drm_update_vblank_count(). + */ + WRITE_ONCE(vblank->enabled, true); } } @@ -1517,7 +1522,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe, * vblank disable, so no need for further locking. The reference from * drm_vblank_get() protects against vblank disable from another source. */ - if (!vblank->enabled) { + if (!READ_ONCE(vblank->enabled)) { ret = -EINVAL; goto err_unlock; } @@ -1644,7 +1649,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data, DRM_WAIT_ON(ret, vblank->queue, 3 * HZ, (((drm_vblank_count(dev, pipe) - vblwait->request.sequence) <= (1 << 23)) || - !vblank->enabled || + !READ_ONCE(vblank->enabled) || !dev->irq_enabled)); }
Order the update to vblank->enabled after the timestamp is primed so that a concurrent unlocked reader will only see the vblank->enabled with the current timestamp. v2: vblank->enable is guarded by dev->vbl_lock not dev->vblank_time_lock, update the READ_ONCE accordingly. Do not add a READ_ONCE(vblank->enabled) inside the interrupt handler to avoid missing an interrupt whilst racing with enable_vblank() Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Daniel Vetter <daniel.vetter@ffwll.ch> --- drivers/gpu/drm/drm_irq.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-)