From d7f32f81cf7579ac7d13127db88e789ea864824c Mon Sep 17 00:00:00 2001 From: Derek Foreman Date: Thu, 24 Nov 2016 12:11:55 -0600 Subject: [PATCH] drm/vc4: Fix race between page flip completion event and clean-up There was a small window where a userspace program could submit a pageflip after receiving a pageflip completion event yet still receive EBUSY. Signed-off-by: Derek Foreman Signed-off-by: Eric Anholt Reviewed-by: Eric Anholt Reviewed-by: Daniel Stone (cherry picked from commit 26fc78f6fef39b9d7a15def5e7e9826ff68303f4) --- drivers/gpu/drm/vc4/vc4_crtc.c | 8 ++++++++ drivers/gpu/drm/vc4/vc4_drv.h | 1 + drivers/gpu/drm/vc4/vc4_kms.c | 33 +++++++++++++++++++++++++-------- 3 files changed, 34 insertions(+), 8 deletions(-) --- a/drivers/gpu/drm/vc4/vc4_crtc.c +++ b/drivers/gpu/drm/vc4/vc4_crtc.c @@ -682,6 +682,14 @@ void vc4_disable_vblank(struct drm_devic CRTC_WRITE(PV_INTEN, 0); } +/* Must be called with the event lock held */ +bool vc4_event_pending(struct drm_crtc *crtc) +{ + struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc); + + return !!vc4_crtc->event; +} + static void vc4_crtc_handle_page_flip(struct vc4_crtc *vc4_crtc) { struct drm_crtc *crtc = &vc4_crtc->base; --- a/drivers/gpu/drm/vc4/vc4_drv.h +++ b/drivers/gpu/drm/vc4/vc4_drv.h @@ -445,6 +445,7 @@ int vc4_bo_stats_debugfs(struct seq_file extern struct platform_driver vc4_crtc_driver; int vc4_enable_vblank(struct drm_device *dev, unsigned int crtc_id); void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id); +bool vc4_event_pending(struct drm_crtc *crtc); int vc4_crtc_debugfs_regs(struct seq_file *m, void *arg); int vc4_crtc_get_scanoutpos(struct drm_device *dev, unsigned int crtc_id, unsigned int flags, int *vpos, int *hpos, --- a/drivers/gpu/drm/vc4/vc4_kms.c +++ b/drivers/gpu/drm/vc4/vc4_kms.c @@ -119,17 +119,34 @@ static int vc4_atomic_commit(struct drm_ /* Make sure that any outstanding modesets have finished. */ if (nonblock) { - ret = down_trylock(&vc4->async_modeset); - if (ret) { + struct drm_crtc *crtc; + struct drm_crtc_state *crtc_state; + unsigned long flags; + bool busy = false; + + /* + * If there's an undispatched event to send then we're + * obviously still busy. If there isn't, then we can + * unconditionally wait for the semaphore because it + * shouldn't be contended (for long). + * + * This is to prevent a race where queuing a new flip + * from userspace immediately on receipt of an event + * beats our clean-up and returns EBUSY. + */ + spin_lock_irqsave(&dev->event_lock, flags); + for_each_crtc_in_state(state, crtc, crtc_state, i) + busy |= vc4_event_pending(crtc); + spin_unlock_irqrestore(&dev->event_lock, flags); + if (busy) { kfree(c); return -EBUSY; } - } else { - ret = down_interruptible(&vc4->async_modeset); - if (ret) { - kfree(c); - return ret; - } + } + ret = down_interruptible(&vc4->async_modeset); + if (ret) { + kfree(c); + return ret; } ret = drm_atomic_helper_prepare_planes(dev, state);