From 7ffd7a68511c710b84db3548a1997fd2625f580a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ville=20Syrj=C3=A4l=C3=A4?= <ville.syrjala@linux.intel.com>
Date: Wed, 6 Aug 2014 14:49:44 +0300
Subject: [PATCH] drm: Always reject drm_vblank_get() after drm_vblank_off()
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Make sure drm_vblank_get() never succeeds when called between
drm_vblank_off() and drm_vblank_on(). Borrow a trick from the
old drm_vblank_{pre,post}_modeset() functions and just bump
the refcount in drm_vblank_off() and drop it in drm_vblank_on().
When drm_vblank_get() encounters a >0 refcount and the vblank
interrupt is already disabled it will simply return -EINVAL.
Hopefully the use of inmodeset won't conflict badly with
drm_vblank_{pre,post}_modeset().
For i915 there's a window between drm_vblank_off() and marking the
crtc as inactive where the current code still allows drm_vblank_get().
v2: Describe what drm_vblank_get() does to explain how
a simple refcount bump manages to fix things (Daniel)
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
drivers/gpu/drm/drm_irq.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 0de123afdb34..b16a63622bad 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1039,6 +1039,15 @@ void drm_vblank_off(struct drm_device *dev, int crtc)
}
spin_unlock(&dev->event_lock);
+ /*
+ * Prevent subsequent drm_vblank_get() from re-enabling
+ * the vblank interrupt by bumping the refcount.
+ */
+ if (!dev->vblank[crtc].inmodeset) {
+ atomic_inc(&dev->vblank[crtc].refcount);
+ dev->vblank[crtc].inmodeset = 1;
+ }
+
spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
}
EXPORT_SYMBOL(drm_vblank_off);
@@ -1079,6 +1088,11 @@ void drm_vblank_on(struct drm_device *dev, int crtc)
unsigned long irqflags;
spin_lock_irqsave(&dev->vbl_lock, irqflags);
+ /* Drop our private "prevent drm_vblank_get" refcount */
+ if (dev->vblank[crtc].inmodeset) {
+ atomic_dec(&dev->vblank[crtc].refcount);
+ dev->vblank[crtc].inmodeset = 0;
+ }
/* re-enable interrupts if there's are users left */
if (atomic_read(&dev->vblank[crtc].refcount) != 0)
WARN_ON(drm_vblank_enable(dev, crtc));