From 43dc7fe2b2118c76fbc2808dec0c57b3158e6dc0 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 17 Mar 2017 20:20:27 +0000 Subject: [PATCH] drm: Mark up accesses of vblank->enabled outside of its spinlock MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Cc: Ville Syrjälä Cc: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/20170317202030.24410-1-chris@chris-wilson.co.uk Reviewed-by: Ville Syrjälä Signed-off-by: Ville Syrjälä --- 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 290e65b93a65..372085561f02 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); @@ -1097,11 +1097,16 @@ 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); } } @@ -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 * drm_vblank_get() protects against vblank disable from another source. */ - if (!vblank->enabled) { + if (!READ_ONCE(vblank->enabled)) { ret = -EINVAL; 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_vblank_count(dev, pipe) - vblwait->request.sequence) <= (1 << 23)) || - !vblank->enabled || + !READ_ONCE(vblank->enabled) || !dev->irq_enabled)); }