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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>
This commit is contained in:
Derek Foreman 2016-11-24 12:11:55 -06:00 committed by Eric Anholt
parent c778cc5df9
commit 26fc78f6fe
3 changed files with 34 additions and 8 deletions
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8
drivers/gpu/drm/vc4/vc4_crtc.c
View File

@ -669,6 +669,14 @@ void vc4_disable_vblank(struct drm_device *dev, unsigned int crtc_id)
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;

1
drivers/gpu/drm/vc4/vc4_drv.h
View File

@ -442,6 +442,7 @@ int vc4_bo_stats_debugfs(struct seq_file *m, void *arg);
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,

33
drivers/gpu/drm/vc4/vc4_kms.c
View File

@ -119,17 +119,34 @@ static int vc4_atomic_commit(struct drm_device *dev,
/* 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);