Messages in this thread Patch in this message | | | From | Greg Kroah-Hartman <> | Subject | [PATCH 4.9 83/93] drm/vc4: Fix race between page flip completion event and clean-up | Date | Mon, 20 Mar 2017 18:51:58 +0100 |
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4.9-stable review patch. If anyone has any objections, please let me know.
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From: Derek Foreman <derekf@osg.samsung.com>
commit 26fc78f6fef39b9d7a15def5e7e9826ff68303f4 upstream.
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> Cc: Amit Pundir <amit.pundir@linaro.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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 @@ -669,6 +669,14 @@ 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 @@ -440,6 +440,7 @@ 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);
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