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drm: Mark up accesses of vblank->enabled outside of its spinlock

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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>
Link: http://patchwork.freedesktop.org/patch/msgid/20170317202030.24410-1-chris@chris-wilson.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
This commit is contained in:
Chris Wilson 2017-03-17 20:20:27 +00:00 • committed by Ville Syrjälä
parent 75cff0837c
commit 43dc7fe2b2
1 changed files with 14 additions and 9 deletions
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23
drivers/gpu/drm/drm_irq.c
View file

@ -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]; struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
unsigned long irqflags; unsigned long irqflags;
assert_spin_locked(&dev->vbl_lock);
/* Prevent vblank irq processing while disabling vblank irqs, /* Prevent vblank irq processing while disabling vblank irqs,
* so no updates of timestamps or count can happen after we've * so no updates of timestamps or count can happen after we've
* disabled. Needed to prevent races in case of delayed irq's. * 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 * calling the ->disable_vblank() operation in atomic context with the
* hardware potentially runtime suspended. * hardware potentially runtime suspended.
*/ */
if (vblank->enabled) { if (cmpxchg_relaxed(&vblank->enabled, true, false))
__disable_vblank(dev, pipe); __disable_vblank(dev, pipe);
vblank->enabled = false;
}
/* /*
* Always update the count and timestamp to maintain the * 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++) { for (pipe = 0; pipe < dev->num_crtcs; pipe++) {
struct drm_vblank_crtc *vblank = &dev->vblank[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)); drm_core_check_feature(dev, DRIVER_MODESET));
del_timer_sync(&vblank->disable_timer); del_timer_sync(&vblank->disable_timer);
@ -1097,11 +1097,16 @@ static int drm_vblank_enable(struct drm_device *dev, unsigned int pipe)
*/ */
ret = __enable_vblank(dev, pipe); ret = __enable_vblank(dev, pipe);
DRM_DEBUG("enabling vblank on crtc %u, ret: %d\n", pipe, ret); DRM_DEBUG("enabling vblank on crtc %u, ret: %d\n", pipe, ret);
if (ret) if (ret) {
atomic_dec(&vblank->refcount); atomic_dec(&vblank->refcount);
else { } else {
vblank->enabled = true;
drm_update_vblank_count(dev, pipe, 0); 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);
} }
} }
@ -1509,7 +1514,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, unsigned int pipe,
* vblank disable, so no need for further locking. The reference from * vblank disable, so no need for further locking. The reference from
* drm_vblank_get() protects against vblank disable from another source. * drm_vblank_get() protects against vblank disable from another source.
*/ */
if (!vblank->enabled) { if (!READ_ONCE(vblank->enabled)) {
ret = -EINVAL; ret = -EINVAL;
goto err_unlock; goto err_unlock;
} }
@ -1636,7 +1641,7 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
DRM_WAIT_ON(ret, vblank->queue, 3 * HZ, DRM_WAIT_ON(ret, vblank->queue, 3 * HZ,
(((drm_vblank_count(dev, pipe) - (((drm_vblank_count(dev, pipe) -
vblwait->request.sequence) <= (1 << 23)) || vblwait->request.sequence) <= (1 << 23)) ||
!vblank->enabled || !READ_ONCE(vblank->enabled) ||
!dev->irq_enabled)); !dev->irq_enabled));
} }