On 8/15/2022 10:08 AM, Stephen Boyd wrote:
Quoting Kuogee Hsieh (2022-08-11 08:20:01)
On 8/10/2022 6:00 PM, Abhinav Kumar wrote:
Even then, you do have a valid point. DRM framework should not have
caused the disable path to happen without an enable.
I went through the stack mentioned in the issue.
Lets see this part of the stack:
dp_ctrl_push_idle+0x40/0x88
dp_bridge_disable+0x24/0x30
drm_atomic_bridge_chain_disable+0x90/0xbc
drm_atomic_helper_commit_modeset_disables+0x198/0x444
msm_atomic_commit_tail+0x1d0/0x374
In drm_atomic_helper_commit_modeset_disables(), we call
disable_outputs().
AFAICT, this is the only place which has a protection to not call the
disable() flow if it was not enabled here:
https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/drm_atomic_helper.c#L1063
But that function is only checking crtc_state->active. Thats set by
the usermode:
https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/drm_atomic_uapi.c#L407
Now, if usermode sets that to true and then crashed it can bypass this
check and we will crash in the location kuogee is trying to fix.
That seems bad, no? We don't want userspace to be able to crash and then
be able to call the disable path when enable never succeeded.
From the issue mentioned in
https://gitlab.freedesktop.org/drm/msm/-/issues/17, the reporter did
mention the usermode crashed.
So this is my tentative analysis of whats happening here.
Ideally yes, we should have been protected by the location mentioned
above in disable_outputs() but looks to me due to the above hypothesis
its getting bypassed.
Can you fix the problem there? Not fixing it means that every driver out
there has to develop the same "fix", when it could be fixed in the core
one time.
The reporter is running GNOME Display Manager (gdm3) instead of chrome.
We can not duplicate this problem locally. Hence we can not confirm this
is the root cause of this bug or not.
Do you know who is more proper to investigate more into this?
Ideally drivers are simple. They configure the hardware for what the
function pointer is asking for. State management and things like that
should be pushed into the core framework so that we don't have to
duplicate that multiple times.
Thanks
Abhinav
Ii sound likes that there is a hole either at user space or drm.
But that should not cause dp_bridge_disable() at dp driver to crash.
Agreed.
Therefore it is properly to check hdp_state condition at
dp_bridge_disable() to prevent it from crashing.
Disagree. Userspace shouldn't be able to get drm into a wedged state.
not sure for this.
I agree if this is simple driver such as i2c which does not need to
maintain any states during operation.
but mdp/dp is far more complexity. we really do not want to have any
crash happen at mdp/dp in the filed.
would you please reconsider our point to add this hdp_state checking
here to prevent any crash happen.
