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 <derekf@osg.samsung.com> Signed-off-by: Eric Anholt <eric@anholt.net> Reviewed-by: Eric Anholt <eric@anholt.net> Reviewed-by: Daniel Stone <daniels@collabora.com>
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@ -669,6 +669,14 @@ void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id)
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CRTC_WRITE(PV_INTEN, 0);
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}
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/* Must be called with the event lock held */
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bool vc4_event_pending(struct drm_crtc *crtc)
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{
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struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
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return !!vc4_crtc->event;
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}
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static void vc4_crtc_handle_page_flip(struct vc4_crtc *vc4_crtc)
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{
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struct drm_crtc *crtc = &vc4_crtc->base;
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@ -442,6 +442,7 @@ int vc4_bo_stats_debugfs(struct seq_file *m, void *arg);
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extern struct platform_driver vc4_crtc_driver;
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int vc4_enable_vblank(struct drm_device *dev, unsigned int crtc_id);
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void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id);
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bool vc4_event_pending(struct drm_crtc *crtc);
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int vc4_crtc_debugfs_regs(struct seq_file *m, void *arg);
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int vc4_crtc_get_scanoutpos(struct drm_device *dev, unsigned int crtc_id,
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unsigned int flags, int *vpos, int *hpos,
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@ -119,17 +119,34 @@ static int vc4_atomic_commit(struct drm_device *dev,
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/* Make sure that any outstanding modesets have finished. */
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if (nonblock) {
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ret = down_trylock(&vc4->async_modeset);
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if (ret) {
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struct drm_crtc *crtc;
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struct drm_crtc_state *crtc_state;
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unsigned long flags;
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bool busy = false;
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/*
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* If there's an undispatched event to send then we're
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* obviously still busy. If there isn't, then we can
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* unconditionally wait for the semaphore because it
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* shouldn't be contended (for long).
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*
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* This is to prevent a race where queuing a new flip
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* from userspace immediately on receipt of an event
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* beats our clean-up and returns EBUSY.
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*/
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spin_lock_irqsave(&dev->event_lock, flags);
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for_each_crtc_in_state(state, crtc, crtc_state, i)
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busy |= vc4_event_pending(crtc);
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spin_unlock_irqrestore(&dev->event_lock, flags);
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if (busy) {
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kfree(c);
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return -EBUSY;
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}
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} else {
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ret = down_interruptible(&vc4->async_modeset);
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if (ret) {
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kfree(c);
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return ret;
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}
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}
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ret = down_interruptible(&vc4->async_modeset);
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if (ret) {
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kfree(c);
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return ret;
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}
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ret = drm_atomic_helper_prepare_planes(dev, state);
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