From: Ville Syrjälä Date: Wed, 6 Aug 2014 11:49:52 +0000 (+0300) Subject: drm: Fix race between drm_vblank_off() and drm_queue_vblank_event() X-Git-Tag: Ubuntu-snapdragon-4.4.0-1050.54~9440^2~39^2~14 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=ffe7c73a8d4f0caeebd5d220ddbf7126a4daca1f;p=mirror_ubuntu-artful-kernel.git drm: Fix race between drm_vblank_off() and drm_queue_vblank_event() Currently it's possible that the following will happen: 1. drm_wait_vblank() calls drm_vblank_get() 2. drm_vblank_off() gets called 3. drm_wait_vblank() calls drm_queue_vblank_event() which adds the event to the queue event though vblank interrupts are currently disabled (and may not be re-enabled ever again). To fix the problem, add another vblank->enabled check into drm_queue_vblank_event(). drm_vblank_off() holds event_lock around the vblank disable, so no further locking needs to be added to drm_queue_vblank_event(). vblank disable from another source is not possible since drm_wait_vblank() already holds a vblank reference. Reviewed-by: Matt Roper Signed-off-by: Ville Syrjälä Signed-off-by: Daniel Vetter --- diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 9353609c6770..b2428cb0c64d 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -1270,6 +1270,7 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe, union drm_wait_vblank *vblwait, struct drm_file *file_priv) { + struct drm_vblank_crtc *vblank = &dev->vblank[pipe]; struct drm_pending_vblank_event *e; struct timeval now; unsigned long flags; @@ -1293,6 +1294,18 @@ static int drm_queue_vblank_event(struct drm_device *dev, int pipe, spin_lock_irqsave(&dev->event_lock, flags); + /* + * drm_vblank_off() might have been called after we called + * drm_vblank_get(). drm_vblank_off() holds event_lock + * around the vblank disable, so no need for further locking. + * The reference from drm_vblank_get() protects against + * vblank disable from another source. + */ + if (!vblank->enabled) { + ret = -EINVAL; + goto err_unlock; + } + if (file_priv->event_space < sizeof e->event) { ret = -EBUSY; goto err_unlock;