On Thu, Dec 06, 2018 at 12:16:53PM +0530, Jayant Shekhar wrote: > _dpu_crtc_vblank_enable_no_lock releases crtc_lock as > its needed for power handle operations. This opens up a > window where in a thread running dpu_crtc_disable and a thread > running dpu_crtc_vblank can race in using dpu_crtc->enabled. Looks like you're using an old kernel. Both power_handle and vblank_enable_no_lock were removed. If you want something more up-to-date for testing, grab the mtp-testing branch from my dpu-staging tree [1] Sean [1]- https://gitlab.freedesktop.org/seanpaul/dpu-staging.git > > dpu_crtc_disable will change the state, where as dpu_crtc_vblank > use the variable. The fix is to cache the crtc enabled state > while holding the lock and use it as a gate in calling > _dpu_crtc_vblank_enable_no_lock. > > This issue was introduced with the commit cf871c48 > (drm/msm/dpu: Remove suspend state tracking from crtc). > > Below are stack traces of thread 1 and thread 2 in good case > and bad case: > > Bad case: > ------------- > Thread 1 > dpu_encoder_phys_vid_control_vblank_irq+0xd0/0x170 > dpu_encoder_register_vblank_callback+0xb8/0x100 > _dpu_crtc_vblank_enable_no_lock+0x240/0x288 > dpu_crtc_disable+0xc4/0x288 > drm_atomic_helper_commit_modeset_disables+0x19c/0x350 > msm_atomic_commit_tail+0x48/0x144 > commit_tail+0x44/0x70 > drm_atomic_helper_commit+0xf0/0xf8 > drm_atomic_commit+0x40/0x4c > drm_mode_atomic_ioctl+0x374/0x90c > drm_ioctl_kernel+0xac/0xec > drm_ioctl+0x218/0x384 > drm_compat_ioctl+0xd8/0xe8 > > Thread 2: > dpu_encoder_phys_vid_control_vblank_irq+0x74/0x170 > dpu_encoder_register_vblank_callback+0xb8/0x100 > _dpu_crtc_vblank_enable_no_lock+0x240/0x288 > dpu_crtc_vblank+0xa8/0x118 > dpu_kms_disable_vblank+0x20/0x2c > vblank_ctrl_worker+0xa0/0xe0 > kthread_worker_fn+0xe4/0x1a4 > kthread+0x11c/0x12c > ret_from_fork+0x10/0x18 > > Good case: > -------------- > Thread 1: > dpu_encoder_phys_vid_control_vblank_irq+0xd0/0x170 > dpu_encoder_phys_vid_irq_control+0xc8/0x110 > _dpu_encoder_irq_control+0x48/0xa0 > _dpu_encoder_resource_control_helper+0xb4/0x10c > dpu_encoder_resource_control+0x4e0/0x664 > dpu_encoder_virt_enable+0xb8/0x120 > dpu_kms_encoder_enable+0x34/0xcc > drm_atomic_helper_commit_modeset_enables+0x120/0x1b8 > msm_atomic_commit_tail+0x5c/0x144 > commit_tail+0x44/0x70 > drm_atomic_helper_commit+0xf0/0xf8 > drm_atomic_commit+0x40/0x4c > drm_mode_atomic_ioctl+0x374/0x90c > > Thread 2: > dpu_crtc_vblank+0xc8/0x118 > dpu_kms_disable_vblank+0x20/0x2c > vblank_ctrl_worker+0xa0/0xe0 > kthread_worker_fn+0xe4/0x1a4 > kthread+0x11c/0x12c > > Signed-off-by: Jayant Shekhar <jshekhar@xxxxxxxxxxxxxx> > --- > drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 17 ++++++++++++++--- > 1 file changed, 14 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c > index 630cbaa..e81ad8c 100644 > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c > @@ -877,6 +877,7 @@ static void dpu_crtc_disable(struct drm_crtc *crtc) > struct drm_encoder *encoder; > struct msm_drm_private *priv; > unsigned long flags; > + bool crtc_en; > > if (!crtc || !crtc->dev || !crtc->dev->dev_private || !crtc->state) { > DPU_ERROR("invalid crtc\n"); > @@ -901,11 +902,21 @@ static void dpu_crtc_disable(struct drm_crtc *crtc) > atomic_read(&dpu_crtc->frame_pending)); > > trace_dpu_crtc_disable(DRMID(crtc), false, dpu_crtc); > - if (dpu_crtc->enabled && dpu_crtc->vblank_requested) { > - _dpu_crtc_vblank_enable_no_lock(dpu_crtc, false); > - } > + > + /* > + * Cache vblank enabled before calling _dpu_crtc_vblank_enable_no_lock, > + * because we release crtc_lock inside and acquire it back. While lock > + * is released, there are cases where dpu_crtc_vblank comes in between > + * while disable is going on. dpu_crtc_vblank further calls > + * _dpu_crtc_vblank_enable_no_lock which tries vblank disable again > + * resulting in refcount mismatch. > + */ > + crtc_en = dpu_crtc->enabled; > dpu_crtc->enabled = false; > > + if (crtc_en && dpu_crtc->vblank_requested) > + _dpu_crtc_vblank_enable_no_lock(dpu_crtc, false); > + > if (atomic_read(&dpu_crtc->frame_pending)) { > trace_dpu_crtc_disable_frame_pending(DRMID(crtc), > atomic_read(&dpu_crtc->frame_pending)); > -- > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > a Linux Foundation Collaborative Project > -- Sean Paul, Software Engineer, Google / Chromium OS
