drm_wait_vblank must be DRM_UNLOCKED because otherwise it will grab the drm_global_mutex and then go to sleep until the vblank event it is waiting for. That can wreck havoc in the windowing system because if one process issues this ioctl, it will block all other processes for the duration of all vblanks between the current and the one it is waiting for. In some cases it can block the entire windowing system.
v2: incorporate comments received from Daniel Vetter and Michel Daenzer.
v3: after a lengty discussion with Daniel Vetter, it was concluded we should not worry about any locking, within drm_wait_vblank function so this patch becomes a rather trivial removal of drm_global_mutex from drm_wait_vblank
Signed-off-by: Ilija Hadzic ihadzic@research.bell-labs.com --- drivers/gpu/drm/drm_drv.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index dbabcb0..dc0eb0b 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -124,7 +124,7 @@ static struct drm_ioctl_desc drm_ioctls[] = { DRM_IOCTL_DEF(DRM_IOCTL_SG_ALLOC, drm_sg_alloc_ioctl, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY), DRM_IOCTL_DEF(DRM_IOCTL_SG_FREE, drm_sg_free, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY),
- DRM_IOCTL_DEF(DRM_IOCTL_WAIT_VBLANK, drm_wait_vblank, 0), + DRM_IOCTL_DEF(DRM_IOCTL_WAIT_VBLANK, drm_wait_vblank, DRM_UNLOCKED),
DRM_IOCTL_DEF(DRM_IOCTL_MODESET_CTL, drm_modeset_ctl, 0),